On 14.08.2019 14:40, Daniel Vetter wrote:
> On Wed, Aug 14, 2019 at 01:04:03PM +0300, Laurent Pinchart wrote:
>> Hi Andrzej,
>>
>> On Wed, Aug 14, 2019 at 08:23:12AM +0200, Andrzej Hajda wrote:
>>> Hi Laurent,
>>>
>>> Sorry for late response.
>> No worries.
>>
>>> On 11.08.2019 00:43, Laurent Pinchart wrote:
>>>> On Fri, Aug 09, 2019 at 01:55:53PM +0200, Andrzej Hajda wrote:
>>>>> On 08.08.2019 21:32, Laurent Pinchart wrote:
>>>>>> On Tue, Jul 16, 2019 at 03:57:21PM +0200, Andrzej Hajda wrote:
>>>>>>> On 16.07.2019 11:00, Daniel Vetter wrote:
>>>>>>>> On Fri, Jul 12, 2019 at 11:01:38AM +0200, Andrzej Hajda wrote:
>>>>>>>>> On 11.07.2019 17:50, Daniel Vetter wrote:
>>>>>>>>>> On Thu, Jul 11, 2019 at 05:12:26PM +0200, Andrzej Hajda wrote:
>>>>>>>>>>> On 11.07.2019 15:18, Daniel Vetter wrote:
>>>>>>>>>>>> On Thu, Jul 11, 2019 at 02:41:01PM +0200, Andrzej Hajda wrote:
>>>>>>>>>>>>> On 11.07.2019 09:35, Daniel Vetter wrote:
>>>>>>>>>>>>>> On Wed, Jul 10, 2019 at 02:12:14PM +0200, Andrzej Hajda wrote:
>>>>>>>>>>>>>>> Hi Laurent,
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> I like the approach, current practice when almost every bridge should
>>>>>>>>>>>>>>> optionally implement connector, or alternatively downstream bridge or
>>>>>>>>>>>>>>> panel is very painful.
>>>>>>>>>>>>>> Yeah I think this looks mostly reasonable. Some api design comments on top
>>>>>>>>>>>>>> of Andrzej', with the fair warning that I didn't bother to read up on how
>>>>>>>>>>>>>> it's all used in the end. I probably should go and do that, at least to
>>>>>>>>>>>>>> get a feeling for what your hpd_cb usually does.
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> More comments inlined.
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> On 07.07.2019 20:18, Laurent Pinchart wrote:
>>>>>>>>>>>>>>>> To support implementation of DRM connectors on top of DRM bridges
>>>>>>>>>>>>>>>> instead of by bridges, the drm_bridge needs to expose new operations and
>>>>>>>>>>>>>>>> data:
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> - Output detection, hot-plug notification, mode retrieval and EDID
>>>>>>>>>>>>>>>> retrieval operations
>>>>>>>>>>>>>>>> - Bitmask of supported operations
>>>>>>>>>>>>>>> Why do we need these bitmask at all? Why cannot we rely on presence of
>>>>>>>>>>>>>>> operation's callback?
>>>>>>>>>>>>>> Yeah also not a huge fan of these bitmasks. Smells like
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> DRIVER_GEM|DRIVER_MODESET, and I personally really hate those. Easy to
>>>>>>>>>>>>>> add, generally good excuse to not have to think through the design between
>>>>>>>>>>>>>> different parts of drivers - "just" add another flag.
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> - Bridge output type
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> Add and document these.
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> Three new bridge helper functions are also added to handle hot plug
>>>>>>>>>>>>>>>> notification in a way that is as transparent as possible for the
>>>>>>>>>>>>>>>> bridges.
>>>>>>>>>>>>>>> Documentation of new opses does not explain how it should cooperate with
>>>>>>>>>>>>>>> bridge chaining, I suppose they should be chained explicitly, am I
>>>>>>>>>>>>>>> right? More comments about it later.
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> Signed-off-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
>>>>>>>>>>>>>>>> ---
>>>>>>>>>>>>>>>> drivers/gpu/drm/drm_bridge.c | 92 +++++++++++++++++++
>>>>>>>>>>>>>>>> include/drm/drm_bridge.h | 170 ++++++++++++++++++++++++++++++++++-
>>>>>>>>>>>>>>>> 2 files changed, 261 insertions(+), 1 deletion(-)
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
>>>>>>>>>>>>>>>> index 519577f363e3..3c2a255df7af 100644
>>>>>>>>>>>>>>>> --- a/drivers/gpu/drm/drm_bridge.c
>>>>>>>>>>>>>>>> +++ b/drivers/gpu/drm/drm_bridge.c
>>>>>>>>>>>>>>>> @@ -70,6 +70,8 @@ static LIST_HEAD(bridge_list);
>>>>>>>>>>>>>>>> */
>>>>>>>>>>>>>>>> void drm_bridge_add(struct drm_bridge *bridge)
>>>>>>>>>>>>>>>> {
>>>>>>>>>>>>>>>> + mutex_init(&bridge->hpd_mutex);
>>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>>> mutex_lock(&bridge_lock);
>>>>>>>>>>>>>>>> list_add_tail(&bridge->list, &bridge_list);
>>>>>>>>>>>>>>>> mutex_unlock(&bridge_lock);
>>>>>>>>>>>>>>>> @@ -86,6 +88,8 @@ void drm_bridge_remove(struct drm_bridge *bridge)
>>>>>>>>>>>>>>>> mutex_lock(&bridge_lock);
>>>>>>>>>>>>>>>> list_del_init(&bridge->list);
>>>>>>>>>>>>>>>> mutex_unlock(&bridge_lock);
>>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>>> + mutex_destroy(&bridge->hpd_mutex);
>>>>>>>>>>>>>>>> }
>>>>>>>>>>>>>>>> EXPORT_SYMBOL(drm_bridge_remove);
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> @@ -463,6 +467,94 @@ void drm_atomic_bridge_enable(struct drm_bridge *bridge,
>>>>>>>>>>>>>>>> }
>>>>>>>>>>>>>>>> EXPORT_SYMBOL(drm_atomic_bridge_enable);
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> +/**
>>>>>>>>>>>>>>>> + * drm_bridge_hpd_enable - enable hot plug detection for the bridge
>>>>>>>>>>>>>>>> + * @bridge: bridge control structure
>>>>>>>>>>>>>>>> + * @cb: hot-plug detection callback
>>>>>>>>>>>>>>>> + * @data: data to be passed to the hot-plug detection callback
>>>>>>>>>>>>>>>> + *
>>>>>>>>>>>>>>>> + * Call &drm_bridge_funcs.hpd_enable and register the given @cb and @data as
>>>>>>>>>>>>>>>> + * hot plug notification callback. From now on the @cb will be called with
>>>>>>>>>>>>>>>> + * @data when an output status change is detected by the bridge, until hot plug
>>>>>>>>>>>>>>>> + * notification gets disabled with drm_bridge_hpd_disable().
>>>>>>>>>>>>>>>> + *
>>>>>>>>>>>>>>>> + * Hot plug detection is supported only if the DRM_BRIDGE_OP_HPD flag is set in
>>>>>>>>>>>>>>>> + * bridge->ops. This function shall not be called when the flag is not set.
>>>>>>>>>>>>>>>> + *
>>>>>>>>>>>>>>>> + * Only one hot plug detection callback can be registered at a time, it is an
>>>>>>>>>>>>>>>> + * error to call this function when hot plug detection is already enabled for
>>>>>>>>>>>>>>>> + * the bridge.
>>>>>>>>>>>>>>>> + */
>>>>>>>>>>>>>>> To simplify architecture maybe would be better to enable hpd just on
>>>>>>>>>>>>>>> bridge attach:
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> bridge->hpd_cb = cb;
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> bridge->hpd_data = data;
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> ret = drm_bridge_attach(...);
>>>>>>>>>>>>>> Yeah I like this more. The other problem here is, what if you need more
>>>>>>>>>>>>>> than 1 callback registers on the same bridge hdp signal?
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> This way we could avoid adding new callbacks hpd_(enable|disable)
>>>>>>>>>>>>>>> without big sacrifices.
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> One more thing: HPD in DisplayPort/HDMI beside signalling plug/unplug,
>>>>>>>>>>>>>>> notifies about sink status change, how it translates to this cb?
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> +void drm_bridge_hpd_enable(struct drm_bridge *bridge,
>>>>>>>>>>>>>>>> + void (*cb)(void *data,
>>>>>>>>>>>>>>>> + enum drm_connector_status status),
>>>>>>>>>>>>>>>> + void *data)
>>>>>>>>>>>>>>>> +{
>>>>>>>>>>>>>>>> + if (!bridge || !bridge->funcs->hpd_enable)
>>>>>>>>>>>>>>>> + return;
>>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>>> + mutex_lock(&bridge->hpd_mutex);
>>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>>> + if (WARN(bridge->hpd_cb, "Hot plug detection already enabled\n"))
>>>>>>>>>>>>>>>> + goto unlock;
>>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>>> + bridge->hpd_cb = cb;
>>>>>>>>>>>>>>>> + bridge->hpd_data = data;
>>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>>> + bridge->funcs->hpd_enable(bridge);
>>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>>> +unlock:
>>>>>>>>>>>>>>>> + mutex_unlock(&bridge->hpd_mutex);
>>>>>>>>>>>>>>>> +}
>>>>>>>>>>>>>>>> +EXPORT_SYMBOL_GPL(drm_bridge_hpd_enable);
>>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>>> +/**
>>>>>>>>>>>>>>>> + * drm_bridge_hpd_disable - disable hot plug detection for the bridge
>>>>>>>>>>>>>>>> + * @bridge: bridge control structure
>>>>>>>>>>>>>>>> + *
>>>>>>>>>>>>>>>> + * Call &drm_bridge_funcs.hpd_disable and unregister the hot plug detection
>>>>>>>>>>>>>>>> + * callback previously registered with drm_bridge_hpd_enable(). Once this
>>>>>>>>>>>>>>>> + * function returns the callback will not be called by the bridge when an
>>>>>>>>>>>>>>>> + * output status change occurs.
>>>>>>>>>>>>>>>> + *
>>>>>>>>>>>>>>>> + * Hot plug detection is supported only if the DRM_BRIDGE_OP_HPD flag is set in
>>>>>>>>>>>>>>>> + * bridge->ops. This function shall not be called when the flag is not set.
>>>>>>>>>>>>>>>> + */
>>>>>>>>>>>>>>>> +void drm_bridge_hpd_disable(struct drm_bridge *bridge)
>>>>>>>>>>>>>>>> +{
>>>>>>>>>>>>>>>> + if (!bridge || !bridge->funcs->hpd_disable)
>>>>>>>>>>>>>>>> + return;
>>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>>> + mutex_lock(&bridge->hpd_mutex);
>>>>>>>>>>>>>>>> + bridge->funcs->hpd_disable(bridge);
>>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>>> + bridge->hpd_cb = NULL;
>>>>>>>>>>>>>>>> + bridge->hpd_data = NULL;
>>>>>>>>>>>>>>>> + mutex_unlock(&bridge->hpd_mutex);
>>>>>>>>>>>>>>>> +}
>>>>>>>>>>>>>>>> +EXPORT_SYMBOL_GPL(drm_bridge_hpd_disable);
>>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>>> +/**
>>>>>>>>>>>>>>>> + * drm_bridge_hpd_notify - notify hot plug detection events
>>>>>>>>>>>>>>>> + * @bridge: bridge control structure
>>>>>>>>>>>>>>>> + * @status: output connection status
>>>>>>>>>>>>>>>> + *
>>>>>>>>>>>>>>>> + * Bridge drivers shall call this function to report hot plug events when they
>>>>>>>>>>>>>>>> + * detect a change in the output status, when hot plug detection has been
>>>>>>>>>>>>>>>> + * enabled by the &drm_bridge_funcs.hpd_enable callback.
>>>>>>>>>>>>>>>> + *
>>>>>>>>>>>>>>>> + * This function shall be called in a context that can sleep.
>>>>>>>>>>>>>>>> + */
>>>>>>>>>>>>>>>> +void drm_bridge_hpd_notify(struct drm_bridge *bridge,
>>>>>>>>>>>>>>>> + enum drm_connector_status status)
>>>>>>>>>>>>>>>> +{
>>>>>>>>>>>>>>>> + mutex_lock(&bridge->hpd_mutex);
>>>>>>>>>>>>>>>> + if (bridge->hpd_cb)
>>>>>>>>>>>>>>>> + bridge->hpd_cb(bridge->hpd_data, status);
>>>>>>>>>>>>>> So this isn't quite what I had in mind. Instead something like this:
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> /* iterates over all bridges in the chain containing @bridge */
>>>>>>>>>>>>>> for_each_bridge(tmp_bridge, bridge) {
>>>>>>>>>>>>>> if (tmp_bridge == bridge)
>>>>>>>>>>>>>> continue;
>>>>>>>>>>>>>> if (bridge->hpd_notify);
>>>>>>>>>>>>>> bridge->hpd_notify(tmp_bridge, bridge, status);
>>>>>>>>>>>>>> }
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> encoder = encoder_for_bridge(bridge);
>>>>>>>>>>>>>> if (encoder->helper_private->bridge_hpd_notify)
>>>>>>>>>>>>>> encoder->helper_private->bridge_hpd_notify(encoder, bridge, status);
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> dev = bridge->dev
>>>>>>>>>>>>>> if (dev->mode_config.helper_private->bridge_hpd_notify)
>>>>>>>>>>>>>> dev->mode_config.helper_private->bridge_hpd_notify(dev, bridge, status)
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> No register callback needed, no locking needed, everyone gets exactly the
>>>>>>>>>>>>>> hpd they want/need.
>>>>>>>>>>>>> As I understand you want to notify every member of the pipeline.
>>>>>>>>>>>>>
>>>>>>>>>>>>> I think it should be enough to notify only the source, and then source
>>>>>>>>>>>>> should decide if/when the hpd should be propagated upstream.
>>>>>>>>>>>>>
>>>>>>>>>>>>> It looks more generic for me.
>>>>>>>>>>>> I'm not parsing ... do you think my idea is more generic and useful, or
>>>>>>>>>>>> the one from Laurent? Kinda confused here.
>>>>>>>>>>> Regarding general idea:
>>>>>>>>>>>
>>>>>>>>>>> 1. Laurent's approach is to notify only consumer, I guess usually video
>>>>>>>>>>> source.
>>>>>>>>>>>
>>>>>>>>>>> 2. Your is to notify all other bridges and encoder.
>>>>>>>>>>>
>>>>>>>>>>> And I prefer 1st approach, why:
>>>>>>>>>>>
>>>>>>>>>>> - the source can decide if/when and to who propagate the signal,
>>>>>>>>>>>
>>>>>>>>>>> - is more generic, for example if bridge send signal to two
>>>>>>>>>>> monitors/panels, it can delay hpd propagation till both sinks are present,
>>>>>>>>>> With Laurent's approach the bridge cannot send the hpd to more than one
>>>>>>>>>> consumer. There's only 1 callback. So you're example doesn't work.
>>>>>>>>> If there will be two consumers, there will be two bridge attachments,
>>>>>>>>> thus there will be two notifications, it should work.
>>>>>>>> 2 consumers, 1 producer. There's only _one_ callback in the producer. The
>>>>>>>> callback is registered on the produce bridge, not on the consumer bridge
>>>>>>>> (or I'm totallly misreading what Laurent does here).
>>>>>>> I have assumed that if devices exposes two hardware sink interfaces it
>>>>>>> will expose two separate bridges - of course it will not work with
>>>>>>> "bridge chaining" thing, but this is a different story.
>>>>>> Daniel is right that the current implementation only allows one
>>>>>> consumer. This is however not a limitation of the API, but of its
>>>>>> implementation, as I only needed a single consumer. The helpers in this
>>>>>> series ensure that neither the consumer nor the producer poke in the
>>>>>> drm_bridge structure to call back to the HPD handler:
>>>>>>
>>>>>> - The consumer calls drm_bridge_hpd_enable() and
>>>>>> drm_bridge_hpd_disable(), which could offer a reference-counted
>>>>>> behaviour if desired without changes to the consumer.
>>>>>>
>>>>>> - The producer gets configured by .hpd_enable() and .hpd_disable(),
>>>>>> which could also easily accommodate reference-counting in the drm
>>>>>> bridge core without changes to the producer.
>>>>>>
>>>>>> - The producer notifies HPD with drm_bridge_hpd_notify(), which could
>>>>>> easily be extended to support multiple consumers without changes to
>>>>>> the producer.
>>>>>>
>>>>>> This is actually my second version of the HPD mechanism. The first
>>>>>> version was never posted, poked into drm_bridge, and required the
>>>>>> producer to be aware of the callbacks. After discussing this privately
>>>>>> with Daniel, I came up with the implementation in this series that,
>>>>>> while not supporting multiple consumers now, makes it easy to extend
>>>>>> later without minimal effort.
>>>>>>
>>>>>> Daniel's proposed implementation above looks reasonable to me, provided
>>>>>> we can iterate over the bridges in an order that don't depend on the
>>>>>> position of the producer in the chain (should be easy to solve by
>>>>>> starting at the encoder for instance). It however looks a bit like a
>>>>>> midlayer to me :-) That's why I have a similar implementation in the
>>>>>> connector-bridge helper, which could be extended to call
>>>>>> encoder->helper_private->bridge_hpd_notify() and
>>>>>> dev->mode_config.helper_private->bridge_hpd_notify() instead of
>>>>>> hardcoding drm_kms_helper_hotplug_event(). Moving the code to
>>>>>> drm_bridge_hpd_notify() would on the other hand set the notification
>>>>>> sequence towards the encoder and driver in stone. Daniel, do you think
>>>>>> that would be better ?
>>>>>>
>>>>>> I would like to remind everybody that this series isn't the last I will
>>>>>> ever submit, and I plan to do more work on drm_bridge and drm_panel. I'm
>>>>>> open to suggestions, and can address problems on top of these patches,
>>>>>> provided obviously that this series doesn't go in the wrong direction.
>>>>>> I'm of course also willing to rework this series, but given the amount
>>>>>> of work we have in the drm_bridge realm, I can't fix everything in one
>>>>>> go :-)
>>>>>>
>>>>>>>>>>> - it resembles hardware wires :)
>>>>>>>>>> This isn't for the hw wires afaiui. The hw hpd terminates in the source
>>>>>>>>>> bridge, which then calls drm_bridge_hpd_notify() to inform anyone else
>>>>>>>>>> interested in that hpd singal. This includes:
>>>>>>>>>> - Other bridges, e.g. if they provide CEC support.
>>>>>>>>>> - Other bridges, maybe they need to re-run the HDCP state engine
>>>>>>>>>> - Overall driver, so it can update the modes/connector status and send the
>>>>>>>>>> uevent to the driver.
>>>>>>>>>> - Overall display pipeline for this specific bridge, maybe you need to
>>>>>>>>>> shut down/re-enable the pipe because $reasons.
>>>>>>>>>>
>>>>>>>>>> That's at least my understanding from lots of chats with Laurent about
>>>>>>>>>> what he wants to do here.
>>>>>> That's correct, and that's what I was trying to implement :-) The
>>>>>> notification, in this patch series, goes from the producer bridge to a
>>>>>> central place (namely the connector, with a helper implementation
>>>>>> available as part of this series, but custom implementations in display
>>>>>> drivers are fine if needed) that then dispatches the notification to all
>>>>>> bridges (through the .lost_hotplug() operation, which we could replace
>>>>>> by an .hpd_notify() operation) for the first two purposes listed above,
>>>>>> and then to the overall driver. The only thing I don't support yet is
>>>>>> dispatching to the display pipeline (item 4 in the list above) as I had
>>>>>> no need for that, and didn't want to develop an API with no user. This
>>>>>> would however not be difficult to do when needed, the need is taken into
>>>>>> account in the proposed implementation.
>>>>>>
>>>>>>>>> I do not know the full picture, but the solution where particular bridge
>>>>>>>>> notifies everything unconditionally seems to me much less flexible.
>>>>>>>>>
>>>>>>>>> If HPD signals is received by the consumer, if there are no obstacles it
>>>>>>>>> can propagate it further, upstream bridge/encoder or to drm core - it
>>>>>>>>> will mimic your scenario.
>>>>>>>>>
>>>>>>>>> But there are also other scenarios where bridge does not want to
>>>>>>>>> propagate signal, because for example:
>>>>>>>>>
>>>>>>>>> - it wants to wait for other sinks to wake up,
>>>>>>>>>
>>>>>>>> The other sink can just do that in their hpd callback.
>>>>>>>>
>>>>>>>>> - it propagates HPD signal via hardware wire,
>>>>>>>> Again, the other sink can just not listen to sw hpd in that case, and use
>>>>>>>> the wire/hw hpd interrupt.
>>>>>>>>
>>>>>>> If it should ignore HPD, why it should receive it at all - it is
>>>>>>> unnecessary noise. And I am afraid with more complicated pipelines it
>>>>>>> will be impossible for particular component (bridge/encoder/whatever) to
>>>>>>> distinguish if HPD notification which came from non-directly connected
>>>>>>> component should be ignored or not.
>>>>>>>
>>>>>>>>> - first it wants to verify if the sink is valid/compatible/authorized
>>>>>>>>> device.
>>>>>>>> Now you lost me. Why would someone glue incompatible IP into a SoC or
>>>>>>>> board?
>>>>>>> Bridge can have external connectors, and the user can connect there
>>>>>>> anything.
>>>>>>>
>>>>>>>>> In general HPD is input signal for notify of state changes on particular
>>>>>>>>> bus, in case of typical video bridge on its output video bus.
>>>>>>>>>
>>>>>>>>> In case of bridges they have also input video buses, and they can send
>>>>>>>>> HPD signal via this bus, but this is indeed different HPD signal, even
>>>>>>>>> if for most cases they looks similar.
>>>>>>>> Ah, I think this is a problem we will eventually have. But it's not
>>>>>>>> something we're currently solving here at all I think.
>>>>>>> Currently sii8620 device in tm2 sends hpd signal upstream via hardware
>>>>>>> line, so this is not something from far future. And I guess with HPD
>>>>>>> broadcasting it could be racy/error prone, for example EDID reading can
>>>>>>> fail due to bridge being not ready (ddc of sii8620 is connected to i2c
>>>>>>> controller via hw wires also).
>>>>>>>
>>>>>>>>>>> And regarding implementation:
>>>>>>>>>>>
>>>>>>>>>>> 1. Laurent proposes to register callback drm_bridge_hpd_enable.
>>>>>>>>>>>
>>>>>>>>>>> 2. You propose to add ops hpd_notify in bridges and encoders.
>>>>>>>>>>>
>>>>>>>>>>> Your proposition is more straightforward, but if we want to notify only
>>>>>>>>>>> source we should locate it by parsing notification chain (what about
>>>>>>>>>>> unchained bridges), or store pointer somewhere during attachment.
>>>>>>>>>>>
>>>>>>>>>>> It still leaves us with this ugly dualism - source is encoder or bridge,
>>>>>>>>>>> similarly to sink as bridge or panel, but fixing it can be done later.
>>>>>>>>>> Uh I think we're not talking about the same thing really. My understanding
>>>>>>>>>> is that this callback is if someone (outside of this bridge) is interested
>>>>>>>>>> in a hpd signal _from_ this bridge. Which means you can only ever have 1
>>>>>>>>>> listener.
>>>>>>>>> Do we have real life examples?
>>>>>>>>>
>>>>>>>>> I want to distinguish two situations:
>>>>>>>>>
>>>>>>>>> - another device wants to know if input bus of the bridge has changed state,
>>>>>>>>>
>>>>>>>>> - another device wants to know if output bus of the bridge has changed
>>>>>>>>> state.
>>>>>>>> Uh, that's what drm_bridge_state is for (if it ever happens). That's how
>>>>>>>> bridges can exchange state and information about each another. hpd is
>>>>>>>> about the physical world, i.e. "is there a cable plugged into the port
>>>>>>>> I'm driving?". We're not going to use fake hpd to update bridge state and
>>>>>>>> fun stuff like that, we have the atomic_check machinery for this.
>>>>>>> My question was if we have real examples that upstream device requires
>>>>>>> knowledge about state of output line of the bridge?
>>>>>>>
>>>>>>> To be more precise, we have following display pipeline:
>>>>>>>
>>>>>>> A-->B-->C
>>>>>>>
>>>>>>> And C sends HPD to B (ie signal that state of line between B and C
>>>>>>> changed). Does A really wants to know this information? or it should
>>>>>>> just need to know if state of line A-->B changed?
>>>>>> There's one real life example, where A is an HDMI encoder, B is an HDMI
>>>>>> ESD protector and level shifter, and C is the physical HDMI connector.
>>>>>> When the HDMI cable is unplugged, the CEC controller part of A needs to
>>>>>> be notified in order to reset the CEC state machine. One could however
>>>>>> argue that in that case the A-B link state changes too, but the
>>>>>> important part is that HPD detection is not performed by A, while A
>>>>>> needs to be informed of lost hotplug.
>>>>> I have no full picture but I guess in this case C sends HPD to B using
>>>>> hardware wire, and then B sends HPD to A also via wire, so I wouldn't
>>>>> say that B does not participate in HPD transmission/forwarding,
>>>> No, in this case A doesn't receive any hardware HPD signal, it requires
>>>> HPD notification through software.
>>>>
>>>>> some shifters with 'advanced power saving' can even perform wake-up of
>>>>> upstream pin logic after receiving HPD on downstream, so HPD sent from B
>>>>> to A is indeed different than HPD sent from C to B.
>>>>>
>>>>> Btw, with the above logic of propagation of HPD callback (proposed by
>>>>> Daniel) I guess it will work this way:
>>>>>
>>>>> - A will receive HPD signal via HW,
>>>>>
>>>>> - then B and C will receive HPD callback via framework.
>>>>>
>>>>> Am I right?
>>>> It's the other way around.
>>>>
>>>> In this case the HPD signal from the connector (C) is routed to an input
>>>> of the ESD chip (B). The ESD chip outputs a shifted HPD hardware signal
>>>> connected to a GPIO of the SoC. The driver for (B) thus registers a GPIO
>>>> IRQ and receive the hardware HPD notification. The driver for the HDMI
>>>> encoder (A) needs to receive HPD notification in software, through the
>>>> framework.
>>> If this is GPIO I wonder why do not query this gpio by encoder directly,
>>> rules of ownership of such gpios seems to be grey area, so in such case
>>> I would advise to put it in the driver who really needs it.
>>>
>>> This way it will be much simpler.
>> First to fall, multiple drivers may need to be informed of HPD events
>> coming from a GPIO, so we would need to duplicate it in multiple places,
>> and I don't think the GPIO framework allows acquiring a GPIO multiple
>> times.
>>
>> Then, the GPIO is described in DT, and DT doesn't care about which
>> driver needs HPD events. DT specifies the GPIO in the node of the device
>> it belongs to, this is defined in DT bindings, and must be the same on
>> all boards, while depending on the board different devices may need to
>> be informed of HPD events.
>>
>> For those two reasons HPD GPIO handling and consumption of HPD events
>> can't always be grouped in the same driver.
>>
>>> Going back to HPD notifications, as I said earlier broadcasting HPD
>>> notification unconditionally to every member of the chain with hope that
>>> the member will be able to filter-out undesired notification seems to me
>>> incorrect - maybe it can solve some problems but is not flexible enough
>>> to be usable in other scenarios.
>>>
>>> If my arguments do not convince you please just continue with your
>>> ideas, we can always add NO_HPD_BROADCAST somewhere :)
>> :-) I would like to understand the problems you're referring to though,
>> and hopefully solve them. If you could describe one of the scenarios
>> where you think this mechanism wouldn't be usable that would help. In
>> the meantime I will post a new version of the series with these
>> operations kept as-is to get the rest of the patches reviewed.
> See my little thing about midlayers, I think midlayers with lots of flags
> for everything aren't a good idea. They should be more opinionated about
> how things work.
>
> So if there's a case where this broadcasting of various things doesn't
> work, let's dig into it.
> -Daniel
OK, almost real life example:
A -> B -> C
A - RGB/HDMI converter,
B - HDMI/MHL converter,
C - uUSB controller (MUIC).
C - detects presence of MHL sink and routes MHL lines to B in such case.
B - has no hardware logic to detect HPD, but it's firmware can read EDID
from downstream component via HW lines and it has hardware lines to
upstream component to send EDID,
A - can read EDID from B via hardware lines, but does not have hardware HPD.
So how it should work (according to specification):
1. C detects MHL sink.
2. C switches his mux to route lines to B.
3. C sends HPD notification to B.
4. B powers on, its firmware reads EDID from downstream lines (possibly
adjusting it) and makes it available to upstream component A.
5. B sends HPD notification to A.
I do not know how it could work with HPD broadcasting.
I guess C should be HPD provider, but in case of HPD broadcasting A and
B would receive notification in the same time, as a result A would start
reading EDID too early - fail.
Regards
Andrzej
>
>>>>>>>>>> You seem to have some other idea here.
>>>>>>>>>>
>>>>>>>>>>>>>>>> + mutex_unlock(&bridge->hpd_mutex);
>>>>>>>>>>>>>>>> +}
>>>>>>>>>>>>>>>> +EXPORT_SYMBOL_GPL(drm_bridge_hpd_notify);
>>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>>> #ifdef CONFIG_OF
>>>>>>>>>>>>>>>> /**
>>>>>>>>>>>>>>>> * of_drm_find_bridge - find the bridge corresponding to the device node in
>>>>>>>>>>>>>>>> diff --git a/include/drm/drm_bridge.h b/include/drm/drm_bridge.h
>>>>>>>>>>>>>>>> index 08dc15f93ded..b9445aa5b1ef 100644
>>>>>>>>>>>>>>>> --- a/include/drm/drm_bridge.h
>>>>>>>>>>>>>>>> +++ b/include/drm/drm_bridge.h
>>>>>>>>>>>>>>>> @@ -23,8 +23,9 @@
>>>>>>>>>>>>>>>> #ifndef __DRM_BRIDGE_H__
>>>>>>>>>>>>>>>> #define __DRM_BRIDGE_H__
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> -#include <linux/list.h>
>>>>>>>>>>>>>>>> #include <linux/ctype.h>
>>>>>>>>>>>>>>>> +#include <linux/list.h>
>>>>>>>>>>>>>>>> +#include <linux/mutex.h>
>>>>>>>>>>>>>>>> #include <drm/drm_mode_object.h>
>>>>>>>>>>>>>>>> #include <drm/drm_modes.h>
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> @@ -334,6 +335,110 @@ struct drm_bridge_funcs {
>>>>>>>>>>>>>>>> */
>>>>>>>>>>>>>>>> void (*atomic_post_disable)(struct drm_bridge *bridge,
>>>>>>>>>>>>>>>> struct drm_atomic_state *state);
>>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>>> + /**
>>>>>>>>>>>>>>>> + * @detect:
>>>>>>>>>>>>>>>> + *
>>>>>>>>>>>>>>>> + * Check if anything is attached to the bridge output.
>>>>>>>>>>>>>>>> + *
>>>>>>>>>>>>>>>> + * This callback is optional, if not implemented the bridge will be
>>>>>>>>>>>>>>>> + * considered as always having a component attached to its output.
>>>>>>>>>>>>>>>> + * Bridges that implement this callback shall set the
>>>>>>>>>>>>>>>> + * DRM_BRIDGE_OP_DETECT flag in their &drm_bridge->ops.
>>>>>>>>>>>>>>>> + *
>>>>>>>>>>>>>>>> + * RETURNS:
>>>>>>>>>>>>>>>> + *
>>>>>>>>>>>>>>>> + * drm_connector_status indicating the bridge output status.
>>>>>>>>>>>>>>>> + */
>>>>>>>>>>>>>>>> + enum drm_connector_status (*detect)(struct drm_bridge *bridge);
>>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>>> + /**
>>>>>>>>>>>>>>>> + * @get_modes:
>>>>>>>>>>>>>>>> + *
>>>>>>>>>>>>>>>> + * Fill all modes currently valid for the sink into the &drm_connector
>>>>>>>>>>>>>>>> + * with drm_mode_probed_add().
>>>>>>>>>>>>>>>> + *
>>>>>>>>>>>>>>>> + * The @get_modes callback is mostly intended to support non-probable
>>>>>>>>>>>>>>>> + * displays such as many fixed panels. Bridges that support reading
>>>>>>>>>>>>>>>> + * EDID shall leave @get_modes unimplemented and implement the
>>>>>>>>>>>>>>>> + * &drm_bridge_funcs->get_edid callback instead.
>>>>>>>>>>>>>>>> + *
>>>>>>>>>>>>>>>> + * This callback is optional. Bridges that implement it shall set the
>>>>>>>>>>>>>>>> + * DRM_BRIDGE_OP_MODES flag in their &drm_bridge->ops.
>>>>>>>>>>>>>>>> + *
>>>>>>>>>>>>>>>> + * RETURNS:
>>>>>>>>>>>>>>>> + *
>>>>>>>>>>>>>>>> + * The number of modes added by calling drm_mode_probed_add().
>>>>>>>>>>>>>>>> + */
>>>>>>>>>>>>>>>> + int (*get_modes)(struct drm_bridge *bridge,
>>>>>>>>>>>>>>>> + struct drm_connector *connector);
>>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>>> + /**
>>>>>>>>>>>>>>>> + * @get_edid:
>>>>>>>>>>>>>>>> + *
>>>>>>>>>>>>>>>> + * Read and parse the EDID data of the connected display.
>>>>>>>>>>>>>>>> + *
>>>>>>>>>>>>>>>> + * The @get_edid callback is the preferred way of reporting mode
>>>>>>>>>>>>>>>> + * information for a display connected to the bridge output. Bridges
>>>>>>>>>>>>>>>> + * that support readind EDID shall implement this callback and leave
>>>>>>>>>>>>>>>> + * the @get_modes callback unimplemented.
>>>>>>>>>>>>>>>> + *
>>>>>>>>>>>>>>>> + * The caller of this operation shall first verify the output
>>>>>>>>>>>>>>>> + * connection status and refrain from reading EDID from a disconnected
>>>>>>>>>>>>>>>> + * output.
>>>>>>>>>>>>>>>> + *
>>>>>>>>>>>>>>>> + * This callback is optional. Bridges that implement it shall set the
>>>>>>>>>>>>>>>> + * DRM_BRIDGE_OP_EDID flag in their &drm_bridge->ops.
>>>>>>>>>>>>>>>> + *
>>>>>>>>>>>>>>>> + * RETURNS:
>>>>>>>>>>>>>>>> + *
>>>>>>>>>>>>>>>> + * An edid structure newly allocated with kmalloc() (or similar) on
>>>>>>>>>>>>>>>> + * success, or NULL otherwise. The caller is responsible for freeing
>>>>>>>>>>>>>>>> + * the returned edid structure with kfree().
>>>>>>>>>>>>>>>> + */
>>>>>>>>>>>>>>>> + struct edid *(*get_edid)(struct drm_bridge *bridge,
>>>>>>>>>>>>>>>> + struct drm_connector *connector);
>>>>>>>>>>>>>>> It overlaps with get_modes, I guess presence of one ops should disallow
>>>>>>>>>>>>>>> presence of another one?
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> I am not really convinced we need this op at all, cannot we just assign
>>>>>>>>>>>>>>> some helper function to .get_modes cb, which will do the same?
>>>>>>>>>>>>>> Plan B): ditch ->get_edid, require that the driver has ->get_modes in that
>>>>>>>>>>>>>> case, and require that if it has an edid it must fill out connector->info
>>>>>>>>>>>>>> and connector->edid correctly.
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> Btw if a hpd happens, who's responible for making sure the edid/mode list
>>>>>>>>>>>>>> in the connector is up-to-date? With your current callback design that's
>>>>>>>>>>>>>> up to the callback, which doesn't feel great. Maybe drm_bridge_hpd_notify
>>>>>>>>>>>>>> should guarantee that it'll first walk the connectors to update status and
>>>>>>>>>>>>>> edid/mode list for the final drm_connector. And then instead of just
>>>>>>>>>>>>>> passing the simple "status", it'll pass the connector, with everything
>>>>>>>>>>>>>> correctly updated.
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> Otherwise everyone interested in that hpd signal will go and re-fetch the
>>>>>>>>>>>>>> edid, which is not so awesome :-)
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>>> + /**
>>>>>>>>>>>>>>>> + * @lost_hotplug:
>>>>>>>>>>>>>>>> + *
>>>>>>>>>>>>>>>> + * Notify the bridge of display disconnection.
>>>>>>>>>>>>>>>> + *
>>>>>>>>>>>>>>>> + * This callback is optional, it may be implemented by bridges that
>>>>>>>>>>>>>>>> + * need to be notified of display disconnection for internal reasons.
>>>>>>>>>>>>>>>> + * One use case is to reset the internal state of CEC controllers for
>>>>>>>>>>>>>>>> + * HDMI bridges.
>>>>>>>>>>>>>>>> + */
>>>>>>>>>>>>>>>> + void (*lost_hotplug)(struct drm_bridge *bridge);
>>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>>> + /**
>>>>>>>>>>>>>>>> + * @hpd_enable:
>>>>>>>>>>>>>>>> + *
>>>>>>>>>>>>>>>> + * Enable hot plug detection. From now on the bridge shall call
>>>>>>>>>>>>>>>> + * drm_bridge_hpd_notify() each time a change is detected in the output
>>>>>>>>>>>>>>>> + * connection status, until hot plug detection gets disabled with
>>>>>>>>>>>>>>>> + * @hpd_disable.
>>>>>>>>>>>>>>>> + *
>>>>>>>>>>>>>>>> + * This callback is optional and shall only be implemented by bridges
>>>>>>>>>>>>>>>> + * that support hot-plug notification without polling. Bridges that
>>>>>>>>>>>>>>>> + * implement it shall also implement the @hpd_disable callback and set
>>>>>>>>>>>>>>>> + * the DRM_BRIDGE_OP_HPD flag in their &drm_bridge->ops.
>>>>>>>>>>>>>>>> + */
>>>>>>>>>>>>>>>> + void (*hpd_enable)(struct drm_bridge *bridge);
>>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>>> + /**
>>>>>>>>>>>>>>>> + * @hpd_disable:
>>>>>>>>>>>>>>>> + *
>>>>>>>>>>>>>>>> + * Disable hot plug detection. Once this function returns the bridge
>>>>>>>>>>>>>>>> + * shall not call drm_bridge_hpd_notify() when a change in the output
>>>>>>>>>>>>>>>> + * connection status occurs.
>>>>>>>>>>>>>>>> + *
>>>>>>>>>>>>>>>> + * This callback is optional and shall only be implemented by bridges
>>>>>>>>>>>>>>>> + * that support hot-plug notification without polling. Bridges that
>>>>>>>>>>>>>>>> + * implement it shall also implement the @hpd_enable callback and set
>>>>>>>>>>>>>>>> + * the DRM_BRIDGE_OP_HPD flag in their &drm_bridge->ops.
>>>>>>>>>>>>>>>> + */
>>>>>>>>>>>>>>>> + void (*hpd_disable)(struct drm_bridge *bridge);
>>>>>>>>>>>>>>>> };
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> /**
>>>>>>>>>>>>>>>> @@ -372,6 +477,38 @@ struct drm_bridge_timings {
>>>>>>>>>>>>>>>> bool dual_link;
>>>>>>>>>>>>>>>> };
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> +/**
>>>>>>>>>>>>>>>> + * enum drm_bridge_ops - Bitmask of operations supported by the bridge
>>>>>>>>>>>>>>>> + */
>>>>>>>>>>>>>>>> +enum drm_bridge_ops {
>>>>>>>>>>>>>>>> + /**
>>>>>>>>>>>>>>>> + * @DRM_BRIDGE_OP_DETECT: The bridge can detect displays connected to
>>>>>>>>>>>>>>>> + * its output. Bridges that set this flag shall implement the
>>>>>>>>>>>>>>>> + * &drm_bridge_funcs->detect callback.
>>>>>>>>>>>>>>>> + */
>>>>>>>>>>>>>>>> + DRM_BRIDGE_OP_DETECT = BIT(0),
>>>>>>>>>>>>>>>> + /**
>>>>>>>>>>>>>>>> + * @DRM_BRIDGE_OP_EDID: The bridge can retrieve the EDID of the display
>>>>>>>>>>>>>>>> + * connected to its output. Bridges that set this flag shall implement
>>>>>>>>>>>>>>>> + * the &drm_bridge_funcs->get_edid callback.
>>>>>>>>>>>>>>>> + */
>>>>>>>>>>>>>>>> + DRM_BRIDGE_OP_EDID = BIT(1),
>>>>>>>>>>>>>>>> + /**
>>>>>>>>>>>>>>>> + * @DRM_BRIDGE_OP_HPD: The bridge can detect hot-plug and hot-unplug
>>>>>>>>>>>>>>>> + * without requiring polling. Bridges that set this flag shall
>>>>>>>>>>>>>>>> + * implement the &drm_bridge_funcs->hpd_enable and
>>>>>>>>>>>>>>>> + * &drm_bridge_funcs->disable_hpd_cb callbacks.
>>>>>>>>>>>>>>>> + */
>>>>>>>>>>>>>>>> + DRM_BRIDGE_OP_HPD = BIT(2),
>>>>>>>>>>>>>>>> + /**
>>>>>>>>>>>>>>>> + * @DRM_BRIDGE_OP_MODES: The bridge can retrieving the modes supported
>>>>>>>>>>>>>>>> + * by the display at its output. This does not include readind EDID
>>>>>>>>>>>>>>>> + * which is separately covered by @DRM_BRIDGE_OP_EDID. Bridges that set
>>>>>>>>>>>>>>>> + * this flag shall implement the &drm_bridge_funcs->get_modes callback.
>>>>>>>>>>>>>>>> + */
>>>>>>>>>>>>>>>> + DRM_BRIDGE_OP_MODES = BIT(3),
>>>>>>>>>>>>>>>> +};
>>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>>> /**
>>>>>>>>>>>>>>>> * struct drm_bridge - central DRM bridge control structure
>>>>>>>>>>>>>>>> */
>>>>>>>>>>>>>>>> @@ -398,6 +535,29 @@ struct drm_bridge {
>>>>>>>>>>>>>>>> const struct drm_bridge_funcs *funcs;
>>>>>>>>>>>>>>>> /** @driver_private: pointer to the bridge driver's internal context */
>>>>>>>>>>>>>>>> void *driver_private;
>>>>>>>>>>>>>>>> + /** @ops: bitmask of operations supported by the bridge */
>>>>>>>>>>>>>>>> + enum drm_bridge_ops ops;
>>>>>>>>>>>>>>>> + /**
>>>>>>>>>>>>>>>> + * @type: Type of the connection at the bridge output
>>>>>>>>>>>>>>>> + * (DRM_MODE_CONNECTOR_*). For bridges at the end of this chain this
>>>>>>>>>>>>>>>> + * identifies the type of connected display.
>>>>>>>>>>>>>>>> + */
>>>>>>>>>>>>>>>> + int type;
>>>>>>>>>>>>>>>> + /** private: */
>>>>>>>>>>>>>>>> + /**
>>>>>>>>>>>>>>>> + * @hpd_mutex: Protects the @hpd_cb and @hpd_data fields.
>>>>>>>>>>>>>>>> + */
>>>>>>>>>>>>>>>> + struct mutex hpd_mutex;
>>>>>>>>>>>>>>>> + /**
>>>>>>>>>>>>>>>> + * @hpd_cb: Hot plug detection callback, registered with
>>>>>>>>>>>>>>>> + * drm_bridge_hpd_enable().
>>>>>>>>>>>>>>>> + */
>>>>>>>>>>>>>>>> + void (*hpd_cb)(void *data, enum drm_connector_status status);
>>>>>>>>>>>>>>>> + /**
>>>>>>>>>>>>>>>> + * @hpd_data: Private data passed to the Hot plug detection callback
>>>>>>>>>>>>>>>> + * @hpd_cb.
>>>>>>>>>>>>>>>> + */
>>>>>>>>>>>>>>>> + void *hpd_data;
>>>>>>>>>>>>>>>> };
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> void drm_bridge_add(struct drm_bridge *bridge);
>>>>>>>>>>>>>>>> @@ -428,6 +588,14 @@ void drm_atomic_bridge_pre_enable(struct drm_bridge *bridge,
>>>>>>>>>>>>>>>> void drm_atomic_bridge_enable(struct drm_bridge *bridge,
>>>>>>>>>>>>>>>> struct drm_atomic_state *state);
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> +void drm_bridge_hpd_enable(struct drm_bridge *bridge,
>>>>>>>>>>>>>>>> + void (*cb)(void *data,
>>>>>>>>>>>>>>>> + enum drm_connector_status status),
>>>>>>>>>>>>>>>> + void *data);
>>>>>>>>>>>>>>>> +void drm_bridge_hpd_disable(struct drm_bridge *bridge);
>>>>>>>>>>>>>>>> +void drm_bridge_hpd_notify(struct drm_bridge *bridge,
>>>>>>>>>>>>>>>> + enum drm_connector_status status);
>>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>>> #ifdef CONFIG_DRM_PANEL_BRIDGE
>>>>>>>>>>>>>>>> struct drm_bridge *drm_panel_bridge_add(struct drm_panel *panel,
>>>>>>>>>>>>>>>> u32 connector_type);
>> --
>> Regards,
>>
>> Laurent Pinchart
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