Hi Luca,
On Wed, Jan 07, 2026 at 10:56:29AM +0100, Luca Ceresoli wrote:
> This driver obtains a bridge pointer from of_drm_find_bridge() in the probe
> function and stores it until driver removal. of_drm_find_bridge() is
> deprecated. Move to of_drm_find_and_get_bridge() for the bridge to be
> refcounted and use bridge->next_bridge to put the reference on
> deallocation.
>
> This needs to be handled in various steps:
>
> * the bridge returned of_drm_get_bridge() is stored in the local temporary
> variable next_bridge whose scope is the for loop, so a cleanup action is
> enough
> * the value of next_bridge is copied into selected_bridge, potentially
> more than once, so a cleanup action at function scope plus a
> drm_bridge_put() in case of reassignment are enough
> * on successful return selected_bridge is stored in bridge->next_bridge,
> which ensures it is put when the bridge is deallocated
>
> Reviewed-by: Maxime Ripard <[email protected]>
> Signed-off-by: Luca Ceresoli <[email protected]>
> ---
> drivers/gpu/drm/bridge/imx/imx8qxp-pixel-link.c | 16 +++++++++-------
> 1 file changed, 9 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/gpu/drm/bridge/imx/imx8qxp-pixel-link.c
> b/drivers/gpu/drm/bridge/imx/imx8qxp-pixel-link.c
> index 91e4f4d55469..b3050310a7f0 100644
> --- a/drivers/gpu/drm/bridge/imx/imx8qxp-pixel-link.c
> +++ b/drivers/gpu/drm/bridge/imx/imx8qxp-pixel-link.c
> @@ -23,7 +23,6 @@
>
> struct imx8qxp_pixel_link {
> struct drm_bridge bridge;
> - struct drm_bridge *next_bridge;
> struct device *dev;
> struct imx_sc_ipc *ipc_handle;
> u8 stream_id;
> @@ -140,7 +139,7 @@ static int imx8qxp_pixel_link_bridge_attach(struct
> drm_bridge *bridge,
> }
>
> return drm_bridge_attach(encoder,
> - pl->next_bridge, bridge,
> + pl->bridge.next_bridge, bridge,
> DRM_BRIDGE_ATTACH_NO_CONNECTOR);
> }
>
> @@ -260,7 +259,7 @@ static int imx8qxp_pixel_link_find_next_bridge(struct
> imx8qxp_pixel_link *pl)
> {
> struct device_node *np = pl->dev->of_node;
> struct device_node *port;
> - struct drm_bridge *selected_bridge = NULL;
> + struct drm_bridge *selected_bridge __free(drm_bridge_put) = NULL;
> u32 port_id;
> bool found_port = false;
> int reg;
> @@ -297,7 +296,8 @@ static int imx8qxp_pixel_link_find_next_bridge(struct
> imx8qxp_pixel_link *pl)
> continue;
> }
>
> - struct drm_bridge *next_bridge = of_drm_find_bridge(remote);
> + struct drm_bridge *next_bridge __free(drm_bridge_put) =
> + of_drm_find_and_get_bridge(remote);
> if (!next_bridge)
> return -EPROBE_DEFER;
>
> @@ -305,12 +305,14 @@ static int imx8qxp_pixel_link_find_next_bridge(struct
> imx8qxp_pixel_link *pl)
> * Select the next bridge with companion PXL2DPI if
> * present, otherwise default to the first bridge
> */
> - if (!selected_bridge || of_property_present(remote,
> "fsl,companion-pxl2dpi"))
> - selected_bridge = next_bridge;
> + if (!selected_bridge || of_property_present(remote,
> "fsl,companion-pxl2dpi")) {
> + drm_bridge_put(selected_bridge);
> + selected_bridge = drm_bridge_get(next_bridge);
Considering selecting the first bridge without the companion pxl2dpi,
there would be a superfluous refcount for the selected bridge:
1) of_drm_find_and_get_bridge: refcount = 1
2) drm_bridge_put: noop, since selected_bridge is NULL, refcount = 1
3) drm_bridge_get: refcount = 2
4) drm_bridge_put(__free): refcount = 1
5) drm_bridge_get: for the pl->bridge.next_bridge, refcount = 2
I think the below snippet would be the right thing to do:
-8<-
{
...
struct drm_bridge *next_bridge __free(drm_bridge_put) =
of_drm_find_and_get_bridge(remote);
if (!next_bridge)
return -EPROBE_DEFER;
/*
* Select the next bridge with companion PXL2DPI if
* present, otherwise default to the first bridge
*/
if (!selected_bridge)
selected_bridge = drm_bridge_get(next_bridge);
if (of_property_present(remote, "fsl,companion-pxl2dpi")) {
if (selected_bridge)
drm_bridge_put(selected_bridge);
selected_bridge = drm_bridge_get(next_bridge);
}
}
...
pl->bridge.next_bridge = selected_bridge;
-8<-
Make sense?
> + }
> }
>
> pl->mst_addr = port_id - 1;
> - pl->next_bridge = selected_bridge;
> + pl->bridge.next_bridge = drm_bridge_get(selected_bridge);
>
> return 0;
> }
>
--
Regards,
Liu Ying
