Hi Maxime, On Mon Nov 24, 2025 at 11:18 AM CET, Maxime Ripard wrote: > On Wed, Nov 19, 2025 at 02:28:41PM +0000, Louis Chauvet wrote: >> On 11/19/25 13:05, Luca Ceresoli wrote: >> > of_drm_find_bridge() does not increment the returned bridge >> > refcount. drm_of_find_bridge() is to be used as a replacement. >> > >> > Suggested-by: Maxime Ripard <[email protected]> >> > Link: >> > https://lore.kernel.org/dri-devel/20250319-stylish-lime-mongoose-0a18ad@houat/ >> > Signed-off-by: Luca Ceresoli <[email protected]> >> > --- >> > drivers/gpu/drm/drm_bridge.c | 7 +++++-- >> > 1 file changed, 5 insertions(+), 2 deletions(-) >> > >> > diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c >> > index d98a7b4a83c0..6debbf20aaa8 100644 >> > --- a/drivers/gpu/drm/drm_bridge.c >> > +++ b/drivers/gpu/drm/drm_bridge.c >> > @@ -299,7 +299,7 @@ EXPORT_SYMBOL(__devm_drm_bridge_alloc); >> > * @bridge: bridge control structure >> > * >> > * Add the given bridge to the global list of bridges, where they can be >> > - * found by users via of_drm_find_bridge(). >> > + * found by users via drm_of_find_bridge(). >> > * >> > * The bridge to be added must have been allocated by >> > * devm_drm_bridge_alloc(). >> > @@ -360,7 +360,7 @@ EXPORT_SYMBOL(devm_drm_bridge_add); >> > * @bridge: bridge control structure >> > * >> > * Remove the given bridge from the global list of registered bridges, so >> > - * it won't be found by users via of_drm_find_bridge(), and add it to the >> > + * it won't be found by users via drm_of_find_bridge(), and add it to the >> > * lingering bridge list, to keep track of it until its allocated memory >> > is >> > * eventually freed. >> > */ >> > @@ -1452,6 +1452,9 @@ EXPORT_SYMBOL(drm_of_find_bridge); >> > * >> > * @np: device node >> > * >> > + * This function is deprecated. Use drm_of_find_bridge() instead for >> > proper >> > + * refcounting. >> > + * >> >> I think it should be more explicit that the refcounting is not done by this >> function, like: >> >> This function is deprecated. The returned bridge is not refcounted, you >> should not use drm_bridge_put(). Use drm_of_find_bridge() instead for proper >> refcounting. > > I'd rather say that the callers must take care of the refcounting by > themselves but that it's racy, or at least that it *must* not use > drm_bridge_put().
I was rather leaning towards "Deprecated. Convert to drm_of_get_bridge().". But if we want to still support existing (lazy) users, with yours and Louis' comments taken into account, what about: * This function is deprecated. Convert to of_drm_get_bridge() instead for * proper refcounting. * * The bridge returned by this function is not refcounted. This is * dangerous because the bridge might be deallocated even before the caller * has a chance to use it. To use this function you have to do one of: * - get a reference with drm_bridge_get() as soon as possible to * minimize the race window, and then drm_bridge_put() when no longer * using the pointer * - not call drm_bridge_get() or drm_bridge_put() at all, which used to * be the correct practice before dynamic bridge lifetime was introduced * - again, convert to of_drm_get_bridge(), which is the only safe thing * to do Luca -- Luca Ceresoli, Bootlin Embedded Linux and Kernel engineering https://bootlin.com
