[PATCH v5] drm/bridge: add of_drm_find_and_get_bridge() and a managed *next_bridge, deprecate of_drm_find_bridge()

[PATCH v5] drm/bridge: add of_drm_find_and_get_bridge() and a managed *next_bridge, deprecate of_drm_find_bridge()

[Luca Ceresoli]

This v4 contains the leftovers of the v3 series that deprecated
of_drm_find_bridge(), added a replacement which handles bridge refcounting,
and converted some of the direct users. All patches have been applied
except the imx8qxp-pixel-link ones, which still need a review for the first
patch.

@Liu, patch 1 is waiting for a review and it's non-trivial, it would be
nice if you could have a look at that one at least.

This is part of the work to support hotplug of DRM bridges. The grand plan
was discussed in [0].

Here's the work breakdown (➜ marks the current series):

 1. ➜ add refcounting to DRM bridges struct drm_bridge,
      based on devm_drm_bridge_alloc()
    A. ✔ add new alloc API and refcounting (v6.16)
    B. ✔ convert all bridge drivers to new API (v6.17)
    C. ✔ kunit tests (v6.17)
    D. ✔ add get/put to drm_bridge_add/remove() + attach/detach()
         and warn on old allocation pattern (v6.17)
    E. ➜ add get/put on drm_bridge accessors
       1. ✔ drm_bridge_chain_get_first_bridge(), add cleanup action (v6.18)
       2. ✔ drm_bridge_get_prev_bridge() (v6.18)
       3. ✔ drm_bridge_get_next_bridge() (v6.19)
       4. ✔ drm_for_each_bridge_in_chain() (v6.19)
       5. ✔ drm_bridge_connector_init (v6.19)
       6. … protect encoder bridge chain with a mutex
       7. ➜ of_drm_find_bridge()
          a. ➜✔… add of_drm_get_bridge(), convert basic direct users
	         (v6.20?, one driver still pending)
	  b. convert other direct users
	  c. convert bridge-only drm_of_find_panel_or_bridge() users
       8. drm_of_find_panel_or_bridge, *_of_get_bridge
       9. ✔ enforce drm_bridge_add before drm_bridge_attach (v6.19)
    F. ✔ debugfs improvements
       1. ✔ add top-level 'bridges' file (v6.16)
       2. ✔ show refcount and list lingering bridges (v6.19)
 2. … handle gracefully atomic updates during bridge removal
    A. ✔ Add drm_dev_enter/exit() to protect device resources (v6.20?)
    B. … protect private_obj removal from list
 3. … DSI host-device driver interaction
 4. ✔ removing the need for the "always-disconnected" connector
 5. finish the hotplug bridge work, moving code to the core and potentially
    removing the hotplug-bridge itself (this needs to be clarified as
    points 1-3 are developed)

[0] https://lore.kernel.org/lkml/20250206-hotplug-drm-bridge-v6-0-9d6f2c9c3058@bootlin.com/#t

Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
---
Changes in v5:
- Changed the only remaining patch after Liu Ying's requests for code
  readability
- Link to v4: https://lore.kernel.org/r/20260107-drm-bridge-alloc-getput-drm_of_find_bridge-v4-0-a62b4399a6bf@bootlin.com

Changes in v4:
- Added review trailers
- Link to v3: https://lore.kernel.org/r/20251216-drm-bridge-alloc-getput-drm_of_find_bridge-v3-0-b5165fab8058@bootlin.com

Changes in v3:
- Completely rewrote using the __drm_bridge_free() idea to prevent
  use-after-free of the next_bridge for the common cases
- Added needed cleanups to the imx8qxp-pixel-link and imx8qxp-pxl2dpi
  drivers
- Removed various patches converting simple cases, to reduce the number of
  e-mails sent; will be moved to the follow-up series
- Link to v2: https://lore.kernel.org/r/20251128-drm-bridge-alloc-getput-drm_of_find_bridge-v2-0-88f8a107eca2@bootlin.com

Changes in v2:
- All patches: renamed drm_of_find_bridge() -> of_drm_get_bridge()
- Various fixes and improvements to patches 1-6, see individual patches
  changelog
- Removed bouncing recipient: Edmund Dea <edmund.j.dea@intel.com>
- Link to v1: https://lore.kernel.org/r/20251119-drm-bridge-alloc-getput-drm_of_find_bridge-v1-0-0db98a7fe474@bootlin.com

---
Luca Ceresoli (1):
      drm/bridge: imx8qxp-pixel-link: get/put the next bridge

 drivers/gpu/drm/bridge/imx/imx8qxp-pixel-link.c | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)
---
base-commit: 4a0f7d0f51c0965a8a394a8c5d65be2d24e362df
change-id: 20251117-drm-bridge-alloc-getput-drm_of_find_bridge-74903367448d

Best regards,
--  
Luca Ceresoli <luca.ceresoli@bootlin.com>

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

[Luca Ceresoli]

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);
+		}
 	}
 
 	pl->mst_addr = port_id - 1;
-	pl->next_bridge = selected_bridge;
 
 	return 0;
 }

-- 
2.52.0

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

[Liu Ying]

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<-

>  	}
>  
>  	pl->mst_addr = port_id - 1;
> -	pl->next_bridge = selected_bridge;
>  
>  	return 0;
>  }
> 

-- 
Regards,
Liu Ying

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

[Luca Ceresoli]

Hello Liu,

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?

Luca

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

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

[Liu Ying]

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

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

[Luca Ceresoli]

Hello Liu,

On Thu Feb 5, 2026 at 10:26 AM CET, Liu Ying wrote:
> 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.

I think this is really a minor detail and there is no obvious "best"
version, so I'll send v6 as I had it ready and build-tested already,
i.e. with the 'else if' version.

Thanks for the discussion!

Luca

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