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
>
> > >>>>>>> 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
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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