On Mon, 5 May 2025 08:23:26 +0200 Maxime Ripard <mrip...@kernel.org> wrote:
> On Mon, Apr 28, 2025 at 05:25:16PM +0200, Luca Ceresoli wrote: > > Hi Maxime, > > > > On Mon, 28 Apr 2025 13:39:23 +0200 > > Maxime Ripard <mrip...@kernel.org> wrote: > > > > > On Thu, Apr 24, 2025 at 10:05:49PM +0200, Luca Ceresoli wrote: > > > > This is the new API for allocating DRM bridges. > > > > > > > > The devm lifetime management of this driver is peculiar. The underlying > > > > device for the panel_bridge is the panel, and the devm lifetime is tied > > > > the > > > > panel device (panel->dev). However the panel_bridge allocation is not > > > > performed by the panel driver, but rather by a separate entity > > > > (typically > > > > the previous bridge in the encoder chain). > > > > > > > > Thus when that separate entoty is destroyed, the panel_bridge is not > > > > removed automatically by devm, so it is rather done explicitly by > > > > calling > > > > drm_panel_bridge_remove(). This is the function that does devm_kfree() > > > > the > > > > panel_bridge in current code, so update it as well to put the bridge > > > > reference instead. > > > > > > > > Signed-off-by: Luca Ceresoli <luca.ceres...@bootlin.com> > > > > > > This looks fine, but we need a TODO entry to clean this up later on, and > > > a comment on devm_drm_put_bridge that this is inherently unsafe and > > > must not be used. > > > > Ah, I see, OK. > > > > Quick draft: > > > > /** > > * devm_drm_put_bridge - Release a bridge reference obtained via devm > > * @dev: device that got the bridge via devm > > * @bridge: pointer to a struct drm_bridge obtained via devm > > * > > * Same as drm_bridge_put() for bridge pointers obtained via devm functions > > * such as devm_drm_bridge_alloc(). > > + * > > + * This function is a temporary workaround and MUST NOT be used. Manual > > + * handling of bridge lifetime is inherently unsafe. > > */ > > That part looks good to me > > > and: > > > > - devm_kfree(panel_bridge->panel->dev, bridge); > > + /* TODO remove this after reworking panel_bridge lifetime */ > > + devm_drm_put_bridge(panel_bridge->panel->dev, bridge); > > } > > > > Does it look good enough? > > That too, but I was talking about an entry in > https://www.kernel.org/doc/html/latest/gpu/todo.html Ah, sure! I queued this for v3, if you have better suggestions don't hesitate to let me know: -----8<----- Remove devm_drm_put_bridge() ---------------------------- Due to how the panel bridge handles the drm_bridge object lifetime, special care must be taken to dispose of the drm_bridge object when the panel_bridge is removed. This is currently managed using devm_drm_put_bridge(), but that is an unsafe, temporary workaround. To fix that, the DRM panel lifetime needs to be reworked. After the rework is done, remove devm_drm_put_bridge() and the TODO in drm_panel_bridge_remove(). Contact: Maxime Ripard <mrip...@kernel.org>, Luca Ceresoli <luca.ceres...@bootlin.com> Level: Intermediate -----8<----- Luca -- Luca Ceresoli, Bootlin Embedded Linux and Kernel engineering https://bootlin.com
