Re: [PATCH RESEND] drm/bridge: drm_bridge_get/put(): document NULL pointer behaviour

[Liu Ying <victor.liu@nxp.com>]

Hi Luca,

On Tue, Mar 24, 2026 at 10:08:49AM +0100, Luca Ceresoli wrote:
> drm_bridge_get and drm_bridge_put() do nothing when they are passed a NULL
> pointer, and they do so since their initial addition in commit 30d1b37d4c02
> ("drm/bridge: add support for refcounting").
> 
> This allows simpler code in various places when using these
> functions. However it's not documented, so it's not clear whether it is
> part of the API "contract" or just a current implementation detail that
> might change in the future.
> 
> There is no visible reason to remove this NULL check, so document it,
> making it part of the contract, letting users count on it.
> 
> Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
> ---
> Historical note: I thought this was documented from the beginning and
> realized it's not the case when someone proposed adding a 'if (bridge)
> drm_bridge_put(bridge)' to a driver [0]. Let's fix it now.
> 
> [0] https://lore.kernel.org/lkml/DG0CHD0TAH9A.27UW4KKY2O9V7@bootlin.com/
> ---
>  drivers/gpu/drm/drm_bridge.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
> index 3b165a0d1e77..3108249a63cd 100644
> --- a/drivers/gpu/drm/drm_bridge.c
> +++ b/drivers/gpu/drm/drm_bridge.c
> @@ -282,7 +282,7 @@ static void __drm_bridge_free(struct kref *kref)
>  
>  /**
>   * drm_bridge_get - Acquire a bridge reference
> - * @bridge: DRM bridge
> + * @bridge: DRM bridge; if NULL this function does nothing
>   *
>   * This function increments the bridge's refcount.
>   *
> @@ -300,7 +300,7 @@ EXPORT_SYMBOL(drm_bridge_get);
>  
>  /**
>   * drm_bridge_put - Release a bridge reference
> - * @bridge: DRM bridge
> + * @bridge: DRM bridge; if NULL this function does nothing

So, we can drop the if(_T) check for cleanup action, right?

DEFINE_FREE(drm_bridge_put, struct drm_bridge *, if (_T) drm_bridge_put(_T))

Reviewed-by: Liu Ying <victor.liu@nxp.com>

>   *
>   * This function decrements the bridge's reference count and frees the
>   * object if the reference count drops to zero.
> 
> ---
> base-commit: a50007089e078a1b7a826559a02277b1601ee189
> change-id: 20260129-drm-bridge-alloc-getput-document-null-check-a551e64b8fc1
> 
> Best regards,

-- 
Regards,
Liu Ying