Commit e46efc6a authored by Luca Ceresoli's avatar Luca Ceresoli
Browse files

drm/bridge: add drm_for_each_bridge_in_chain_scoped() 



drm_for_each_bridge_in_chain() iterates ofer the bridges in an encoder
chain without protecting the lifetime of the bridges using
drm_bridge_get/put(). This creates a risk window where the bridge could be
freed while iterating on it. Users of drm_for_each_bridge_in_chain() cannot
solve this reliably.

Add variant of drm_for_each_bridge_in_chain() that gets/puts the bridge
reference at the beginning/end of each iteration, and puts it if breaking
ot of the loop.

Note that this requires adding a new drm_bridge_get_next_bridge_and_put()
function because, unlike similar functions as __of_get_next_child(),
drm_bridge_get_next_bridge() gets the "next" pointer but does not put the
"prev" pointer. Unfortunately drm_bridge_get_next_bridge() cannot be
modified to put the "prev" pointer because some of its users rely on
this, such as drm_atomic_bridge_propagate_bus_flags().

Also deprecate drm_for_each_bridge_in_chain(), in preparation for removing
it after converting all users to the scoped version.

Reviewed-by: default avatarMaxime Ripard <mripard@kernel.org>
Link: https://lore.kernel.org/r/20250808-drm-bridge-alloc-getput-for_each_bridge-v2-3-edb6ee81edf1@bootlin.com


Signed-off-by: default avatarLuca Ceresoli <luca.ceresoli@bootlin.com>
parent c92f59ba

.clang-format

+1 −0
Original line number Diff line number Diff line
@@ -168,6 +168,7 @@ ForEachMacros: 
  - 'drm_exec_for_each_locked_object'

  - 'drm_exec_for_each_locked_object_reverse'

  - 'drm_for_each_bridge_in_chain'

  - 'drm_for_each_bridge_in_chain_scoped'

  - 'drm_for_each_connector_iter'

  - 'drm_for_each_crtc'

  - 'drm_for_each_crtc_reverse'

include/drm/drm_bridge.h

+41 −0
Original line number Diff line number Diff line
@@ -1440,10 +1440,51 @@ drm_bridge_chain_get_last_bridge(struct drm_encoder *encoder) 
 *	    iteration

 *

 * Iterate over all bridges present in the bridge chain attached to @encoder.

 *

 * This is deprecated, do not use!

 * New drivers shall use drm_for_each_bridge_in_chain_scoped().

 */

#define drm_for_each_bridge_in_chain(encoder, bridge)			\

	list_for_each_entry(bridge, &(encoder)->bridge_chain, chain_node)



/**

 * drm_bridge_get_next_bridge_and_put - Get the next bridge in the chain

 *                                      and put the previous

 * @bridge: bridge object

 *

 * Same as drm_bridge_get_next_bridge() but additionally puts the @bridge.

 *

 * RETURNS:

 * the next bridge in the chain after @bridge, or NULL if @bridge is the last.

 */

static inline struct drm_bridge *

drm_bridge_get_next_bridge_and_put(struct drm_bridge *bridge)

{

	struct drm_bridge *next = drm_bridge_get_next_bridge(bridge);



	drm_bridge_put(bridge);



	return next;

}



/**

 * drm_for_each_bridge_in_chain_scoped - iterate over all bridges attached

 *                                       to an encoder

 * @encoder: the encoder to iterate bridges on

 * @bridge: a bridge pointer updated to point to the current bridge at each

 *	    iteration

 *

 * Iterate over all bridges present in the bridge chain attached to @encoder.

 *

 * Automatically gets/puts the bridge reference while iterating, and puts

 * the reference even if returning or breaking in the middle of the loop.

 */

#define drm_for_each_bridge_in_chain_scoped(encoder, bridge)		\

	for (struct drm_bridge *bridge __free(drm_bridge_put) =		\

	     drm_bridge_chain_get_first_bridge(encoder);		\

	     bridge;							\

	     bridge = drm_bridge_get_next_bridge_and_put(bridge))



enum drm_mode_status

drm_bridge_chain_mode_valid(struct drm_bridge *bridge,

			    const struct drm_display_info *info,