Re: [PATCH 09/60] drm/bridge: Add connector-related bridge operations and data

[Daniel Vetter <daniel@ffwll.ch>]

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@ideasonboard.com>
> > ---
> >  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.

> > +	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 :-)
-Daniel

> 
> 
> Regards
> 
> Andrzej
> 
> 
> > +
> > +	/**
> > +	 * @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);
> 
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
_______________________________________________
dri-devel mailing list
dri-devel@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/dri-devel