Re: [PATCH v6 04/51] drm/bridge: Add connector-related bridge operations and data

Hi Daniel,

On Mon, Feb 17, 2020 at 10:53:08AM +0100, Daniel Vetter wrote:

On Sun, Feb 16, 2020 at 11:02:21PM +0200, 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
• Bridge output type
• I2C adapter for DDC access

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.

Signed-off-by: Laurent Pinchart laurent.pinchart@ideasonboard.com Reviewed-by: Boris Brezillon boris.brezillon@collabora.com Reviewed-by: Sam Ravnborg sam@ravnborg.org

---

Changes since v3:

• Fix typos

Changes since v2:

• Add wrappers around the .detect(), .get_modes() and .get_edid() operations
• Warn bridge drivers about valid usage of the connector argument to .get_modes() and .get_edid()

Changes since v1:

• Make .hpd_enable() and .hpd_disable() optional
• Rename .lost_hotplug() to .hpd_notify()
• Add ddc field to drm_bridge

---

drivers/gpu/drm/drm_bridge.c | 162 +++++++++++++++++++++++++++++ include/drm/drm_bridge.h | 192 ++++++++++++++++++++++++++++++++++- 2 files changed, 353 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c index 68ab933ee430..78d26a9a3ee6 100644 --- a/drivers/gpu/drm/drm_bridge.c +++ b/drivers/gpu/drm/drm_bridge.c @@ -71,6 +71,8 @@ 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);

@@ -87,6 +89,8 @@ 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);

@@ -919,6 +923,164 @@ int drm_atomic_bridge_chain_check(struct drm_bridge *bridge, } EXPORT_SYMBOL(drm_atomic_bridge_chain_check);

+/**

• • drm_bridge_detect - check if anything is attached to the bridge output
• • @bridge: bridge control structure
• • If the bridge supports output detection, as reported by the
• • DRM_BRIDGE_OP_DETECT bridge ops flag, call &drm_bridge_funcs.detect for the
• • bridge and return the connection status. Otherwise return
• • connector_status_unknown.
• • RETURNS:
• • The detection status on success, or connector_status_unknown if the bridge
• • doesn't support output detection.
• */

+enum drm_connector_status drm_bridge_detect(struct drm_bridge *bridge) +{

• if (!(bridge->ops & DRM_BRIDGE_OP_DETECT))

• return connector_status_unknown;
  

• return bridge->funcs->detect(bridge);

+} +EXPORT_SYMBOL_GPL(drm_bridge_detect);

+/**

• • drm_bridge_get_modes - fill all modes currently valid for the sink into the
• • @connector
• • @bridge: bridge control structure
• • @connector: the connector to fill with modes
• • If the bridge supports output modes retrieval, as reported by the
• • DRM_BRIDGE_OP_MODES bridge ops flag, call &drm_bridge_funcs.get_modes to
• • fill the connector with all valid modes and return the number of modes
• • added. Otherwise return 0.
• • RETURNS:
• • The number of modes added to the connector.
• */

+int drm_bridge_get_modes(struct drm_bridge *bridge,

• 	 struct drm_connector *connector)
  

+{

• if (!(bridge->ops & DRM_BRIDGE_OP_MODES))

• return 0;
  

• return bridge->funcs->get_modes(bridge, connector);

+} +EXPORT_SYMBOL_GPL(drm_bridge_get_modes);

+/**

• • drm_bridge_get_edid - get the EDID data of the connected display
• • @bridge: bridge control structure
• • @connector: the connector to read EDID for
• • If the bridge supports output EDID retrieval, as reported by the
• • DRM_BRIDGE_OP_EDID bridge ops flag, call &drm_bridge_funcs.get_edid to
• • get the EDID and return it. Otherwise return ERR_PTR(-ENOTSUPP).
• • RETURNS:
• • The retrieved EDID on success, or an error pointer otherwise.
• */

+struct edid *drm_bridge_get_edid(struct drm_bridge *bridge,

• 		 struct drm_connector *connector)
  

+{

• if (!(bridge->ops & DRM_BRIDGE_OP_EDID))

• return ERR_PTR(-ENOTSUPP);
  

• return bridge->funcs->get_edid(bridge, connector);

+} +EXPORT_SYMBOL_GPL(drm_bridge_get_edid);

+/**

• • 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 if implemented 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.
• */

+void drm_bridge_hpd_enable(struct drm_bridge *bridge,

• 	   void (*cb)(void *data,
  

• 		      enum drm_connector_status status),
  

• 	   void *data)
  

+{

• if (!bridge || !(bridge->ops & DRM_BRIDGE_OP_HPD))

Supplying a NULL bridge is a caller bug imo, and you're inconsistent in handling this. Imo just drop.

Sounds good to me, I'll drop it.

...

• 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;
• if (bridge->funcs->hpd_enable)

• 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 if implemented 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->ops & DRM_BRIDGE_OP_HPD))

• return;
  

• mutex_lock(&bridge->hpd_mutex);
• if (bridge->funcs->hpd_disable)

• 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 drm_bridge_hpd_enable().
• • 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);
  

• 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 45626ecf20f8..ba9b7c84f11e 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_atomic.h> #include <drm/drm_encoder.h> @@ -33,7 +34,10 @@

struct drm_bridge; struct drm_bridge_timings; +struct drm_connector; struct drm_panel; +struct edid; +struct i2c_adapter;

/**

• struct drm_bridge_funcs - drm_bridge control functions

@@ -488,6 +492,119 @@ struct drm_bridge_funcs { * giving the reason of the failure otherwise. */ struct drm_bridge_state *(*atomic_reset)(struct drm_bridge *bridge);

• /**

• * @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-probeable
  

• * 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.
  

• *
  

• * The connector parameter shall be used for the sole purpose of
  

• * filling modes, and shall not be stored internally by bridge drivers
  

• * for future usage.
  

• *
  

• * 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 reading 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.
  

• *
  

• * The connector parameter shall be used for the sole purpose of EDID
  

• * retrieval and parsing, and shall not be stored internally by bridge
  

• * drivers for future usage.
  

• *
  

• * 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);
  

• /**

• * @hpd_notify:
  

• *
  

• * Notify the bridge of hot plug detection.
  

• *
  

• * This callback is optional, it may be implemented by bridges that
  

• * need to be notified of display connection or disconnection for
  

• * internal reasons. One use case is to reset the internal state of CEC
  

• * controllers for HDMI bridges.
  

• */
  

• void (*hpd_notify)(struct drm_bridge *bridge,

• 	   enum drm_connector_status status);
  

• /**

• * @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);

};

/** @@ -526,6 +643,39 @@ 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->hpd_disable callbacks if they support enabling
  

• * and disabling hot-plug detection dynamically.
  

• */
  

• DRM_BRIDGE_OP_HPD = BIT(2),
• /**

• * @DRM_BRIDGE_OP_MODES: The bridge can retrieve the modes supported
  

• * by the display at its output. This does not include reading 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),

+};

I still don't like this one here, since most of them are tracking redundant information. If you don't like just checking for the hook directly wrap it in a helper, e.g.

bool drm_bridge_supports_detect(bridge) { return bridge->ops->detect; }

It seems I've done a really bad job explaining why the flags are required, so let me try again :-)

There's a difference between supporting an operation in a driver, and supporting it in a given system. When a bridge hardware supports reading EDID, or detecting hotplug, the driver will implement this and expose the corresponding operation in drm_bridge_funcs by setting the function pointers appropriately.

However, this doesn't mean that the DDC lines are wired to the bridge on a particular board, they could be connected to an I2C controller of the SoC. Same for the HPD line, it could be connected to a GPIO instead of a dedicated pin of the bridge. This board-specific information is reported by the firmware (ACPI or DT), parsed by the bridge driver, and reflected in the drm_bridge_ops flags.

drm_bridge_funcs and drm_bridge_ops are thus different, the latter supplements the former. We could merge the two by setting the corresponding function pointer in drm_bridge_funcs to NULL when the drm_bridge_ops flag isn't set. This would however require allocating drm_bridge_funcs dynamically (either by embedding it into a driver-specific structure, or allocating it dynamically directly) instead of using a global static const struct, and this is considered to be a security issue as it allows a potential attacker to overwrite function pointers (there have been quite a lot of security patches merged that move function pointers to .rodata or otherwise const memory).

hpd seems to be special, since a bridge can support hotplug but not have the enable_hpd/disable_hpd hooks. Which smells somewhat fishy, since if you have multiple bridges with hpd, how do you make sure you get hpd events only from the right one?

On a given board HPD should only be generated by one bridge in practice. If we ever encounter systems where multiple bridges can generate HPD for the same external HPD event, I think we can deal with them at that time.

Aside from that just having a

bool supports_hpd;

seems a lot simpler.

If we only needed DRM_BRIDGE_OP_HPD, I agree that a bool would be simpler, but as explained above we need the other ones too :-)

Yes I know that the drm DRIVER_FOO flags don't work like that, and I'm kinda unhappy about them since forever. Managed to delete most of them even :-)

...

/**

• struct drm_bridge - central DRM bridge control structure

*/ @@ -554,6 +704,33 @@ 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;
• /**

• * @ddc: Associated I2C adapter for DDC access, if any.
  

• */
  

• struct i2c_adapter *ddc;
• /** 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;

};

static inline struct drm_bridge * @@ -660,6 +837,19 @@ drm_atomic_helper_bridge_propagate_bus_fmt(struct drm_bridge *bridge, u32 output_fmt, unsigned int *num_input_fmts);

+enum drm_connector_status drm_bridge_detect(struct drm_bridge *bridge); +int drm_bridge_get_modes(struct drm_bridge *bridge,

• 	 struct drm_connector *connector);
  

+struct edid *drm_bridge_get_edid(struct drm_bridge *bridge,

• 		 struct drm_connector *connector);
  

+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); struct drm_bridge *drm_panel_bridge_add_typed(struct drm_panel *panel,