On Thu, Aug 08, 2019 at 09:19:48PM +0300, Laurent Pinchart wrote:
> Hello Daniel and Andrzej,
>
> On Thu, Jul 11, 2019 at 09:35:48AM +0200, 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.
>
> The reason is that a bridge may support an operation (as in implemented
> in the bridge hardware), but that operation may not be supported on a
> particular board. For instance an HDMI encoder may support reading EDID
> when the DDC lines are connected to the encoder, but a board may connect
> the DDC lines to an I2C port of the SoC. We thus need to decouple
> if a particular instance of the device supports the operation (exposed
> by the ops flags) from the function pointers.
>
> We could of course allocate the drm_bridge_funcs structure dynamically
> for each bridge instance, and fill it with function pointers manually,
> leaving the unused ops always NULL, but that would require making the
> structure writable, which is considered a security issue. That's why I
> decided to keep the drm_bridge_funcs structure as a global static const
> structure, and add an ops bitmask.
Yeah reallocating func structures is not great, I agree ...
Would an -ENXIO at runtime work too? Or do we need to know this
statically. It just feels so silly and redundant to have the flag and the
hook.
> > > > - 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.
>
> No, the whole point is that they should not be chained at all. A bridge
> does not have to propagate, for instance, .get_edid() to the next
> bridge. That's one of the core design principles in this series, I want
> to keep the bridges as simple as possible, and move the complexity of
> the boilerplate code that is currently copied all around to helpers. See
> patch "drm: Add helper to create a connector for a chain of bridges" for
> more information about how this is used, with a helper that delegates
> the connector operations to the correct bridge in the chain based on the
> ops reported by each bridge.
Sounds like we have a general discussion of who should be owning the
topology around bridges. I guess there's arguments for both positions ...
Not sure what to do, aside from that I'm not a huge fan of flags
everywhere. But if that's the best we can do, so be it :-/
-Daniel
>
> > > > 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?
>
> That's why I decided to hide hide HPD through helpers,
> drm_bridge_hpd_enable() and drm_bridge_hpd_disable() on the listener
> side, and drm_bridge_hpd_notify() on the event reporter side. While the
> current implementation is limited to a single listener, only the helpers
> would need to be changed to extend that to multiple listeners.
>
> Note that the .hpd_enable() and .hpd_disable() operations also allow the
> bridge to disable HPD detection when not used. Doing so keeps the bridge
> simple, it only needs to care about reporting HPD events when they're
> enabled, without caring who (if anyone) is listening, and gets clear
> instructions on whether to enable or disable the HPD hardware (in case
> it can be disabled).
>
> > > 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?
>
> This is something this series doesn't implement. I don't think it would
> be a big deal, but my knowledge of HPD (especially for DisplayPort) ends
> here. If you can elaborate on what would be needed, I can implement
> that.
>
> > > > +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.
>
> I'll reply to this further down the mail thread, to address additional
> comments.
>
> > > > + 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.
>
> I think that's doable, I'll have a look.
>
> > 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 :-)
>
> With the current design there's a single listener, so it's not a big
> deal :-) Furthermore, the listener is the helper that creates a
> connector on top of a chain of bridges, so it's a pretty good place to
> handle this. See the call to drm_kms_helper_hotplug_event() in
> drm_bridge_connector_hpd_cb().
>
> I'm all for reworking HPD and mode fetching, but I think it's a bit too
> big of a requirement as a prerequisite for this series (or as part of
> this series). We have hardware that can report HPD with various level of
> details (from "something happened on a connector" to "this particular
> event happened on this particular connector"), and we channel that
> through helpers such as drm_kms_helper_hotplug_event() that lose the
> details and go through a heavy mechanism to refetch everything. I
> understand this is needed in many cases, but I think there's room for
> improvement. This series, in my opinion, doesn't go in the wrong
> direction in that regard, as it eventually calls
> drm_kms_helper_hotplug_event(), so I think improvements would make sense
> on top of it. I'm even willing to work on this, provided I get feedback
> on what is desired.
>
> > > > + /**
> > > > + * @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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