Re: [PATCH v5] drm/bridge: imx8qxp-pixel-link: get/put the next bridge

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

On Thu, Feb 05, 2026 at 09:52:04AM +0100, Luca Ceresoli wrote:
> Hello Liu,

Hello Luca,

> 
> On Wed Feb 4, 2026 at 7:27 AM CET, Liu Ying wrote:
>> Hi Luca,
>>
>> On Tue, Feb 03, 2026 at 11:35:25AM +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.
>>>
>>> To keep the code as simple and reliable as possible, get a reference for
>>> each pointer that stores a drm_bridge address when it is stored and release
>>> it when the pointer is overwritten or goes out of scope. Also remove the
>>> intermediate selected_bridge variable to reduce the refcounted variables in
>>> the function. The involved pointers are:
>>>
>>>  * next_bridge loop-local variable:
>>>    - get reference by of_drm_find_and_get_bridge()
>>>    - put reference at the end of the loop iteration (__free)
>>>
>>>  * pl->bridge.next_bridge, tied to struct imx8qxp_pixel_link lifetime:
>>>    - get reference when assigned (by copy from next_bridge)
>>>    - put reference before reassignment if reassignment happens
>>>    - put reference when the struct imx8qxp_pixel_link embedding the
>>>      struct drm_bridge is destroyed (struct drm_bridge::next_bridge)
>>>
>>> Additionally, split the somewhat complex if() for readability.
>>>
>>> Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
>>>
>>> ---
>>>
>>> Changes in v5:
>>> - rewrite commit message after Liu's review to clarify the per-pointer
>>>   get/put idea
>>> - split the if()s involved in selcting the bridge
>>> - remove intermediate selected_bridge pointer
>>> - removed Maxime's R-by, patch changed
>>> ---
>>>  drivers/gpu/drm/bridge/imx/imx8qxp-pixel-link.c | 17 ++++++++++-------
>>>  1 file changed, 10 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..e29e099b893a 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 +259,6 @@ 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;
>>>  	u32 port_id;
>>>  	bool found_port = false;
>>>  	int reg;
>>> @@ -297,7 +295,8 @@ 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 +304,16 @@ 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 (!pl->bridge.next_bridge)
>>> +			pl->bridge.next_bridge = drm_bridge_get(next_bridge);
>>> +
>>> +		if (of_property_present(remote, "fsl,companion-pxl2dpi")) {
>>> +			drm_bridge_put(pl->bridge.next_bridge);
>>> +			pl->bridge.next_bridge = drm_bridge_get(next_bridge);
>>> +		}
>>
>> Can you drop the intermediate next_bridge variable to simplify the code?
>>
>> -8<-
>> if (!pl->bridge.next_bridge) {
>>         pl->bridge.next_bridge = of_drm_find_and_get_bridge(remote);
>>         if (!pl->bridge.next_bridge)
>>                 return -EPROBE_DEFER;
>> }
>>
>> if (of_property_present(remote, "fsl,companion-pxl2dpi")) {
>>         drm_bridge_put(pl->bridge.next_bridge);
>>         pl->bridge.next_bridge = of_drm_find_and_get_bridge(remote);
>>         if (!pl->bridge.next_bridge)
>>                 return -EPROBE_DEFER;
>> }
>> -8<-
> 
> Potentially calling of_drm_find_and_get_bridge() twice on the same node,
> with a put in the middle, looks poorly readable to me, even though it still
> looks correct code.
> 
> However I think we can do even better with an 'else if':
> 
>   if (!pl->bridge.next_bridge) {
>          pl->bridge.next_bridge = of_drm_find_and_get_bridge(remote);
>          if (!pl->bridge.next_bridge)
>                  return -EPROBE_DEFER;
>   } else if (of_property_present(remote, "fsl,companion-pxl2dpi")) {   <===
>          drm_bridge_put(pl->bridge.next_bridge);
>          pl->bridge.next_bridge = of_drm_find_and_get_bridge(remote);
>          if (!pl->bridge.next_bridge)
>                  return -EPROBE_DEFER;
>   }
> 
> Looks OK?

Both are fine to me.  TBH, I feel my version with two 'if's is a bit easier
to read.  But, I'd say up to you.

> 
> Luca
> 
> --
> Luca Ceresoli, Bootlin
> Embedded Linux and Kernel engineering
> https://bootlin.com/

-- 
Regards,
Liu Ying