Re: [PATCH] drm/omap: dss: fix handling deferrals

["Luca Ceresoli" <luca.ceresoli@bootlin.com>]

Hello Andreas,

On Wed Nov 11, 2026 at 3:56 PM CET, Tomi Valkeinen wrote:
> Hi,
>
> On 11/11/2026 14:22, Andreas Kemnade wrote:
>> Forward the error given by of_drm_get_bridge_by_endpoint() if it is
>> EPROBE_DEFER to ensure output gets initialized later when available.
>>
>> On GTA04/OMAP3 no display was found, but it appeared after doing
>> rmmod omapdrm ; modprobe omapdrm
>>
>> Fixes: b7e9b93fc8ecf ("drm/omap: dss: don't create a panel_bridge")

Ouch, sorry about breaking this driver. To my excuse the old code removed
by b7e9b93fc8ecf was (ans still is) pretty obscure.

>> Signed-off-by: Andreas Kemnade <andreas@kemnade.info>
>> ---
>>   drivers/gpu/drm/omapdrm/dss/output.c | 5 +++++
>>   1 file changed, 5 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/omapdrm/dss/output.c b/drivers/gpu/drm/omapdrm/dss/output.c
>> index 36d37deac8026..220ed7e003080 100644
>> --- a/drivers/gpu/drm/omapdrm/dss/output.c
>> +++ b/drivers/gpu/drm/omapdrm/dss/output.c
>> @@ -24,6 +24,11 @@ int omapdss_device_init_output(struct omap_dss_device *out,
>>
>>   	bridge = of_drm_get_bridge_by_endpoint(out->dev->of_node, out->of_port, 0);
>>   	if (IS_ERR(bridge)) {
>> +		if (PTR_ERR(bridge) == -EPROBE_DEFER) {
>> +			ret = PTR_ERR(bridge);
>> +			goto error;
>> +		}
>> +
> Shouldn't we just return PTR_ERR(bridge) here? The error label will call
> omapdss_device_cleanup_output(), which cleans up things set up later in
> this function.

Indeed.


Additionally, by looking at the omapdss_device_init_output() code right
now, the goto-based error management appears:

 1. unnecessarily complicated: only one goto for only one line of rollback
    code

 2. potentially wrong, or at least doing too much, because
    omapdss_device_cleanup_output() does two things:

      a. drm_bridge_put(out->next_bridge): but when goto is invoked the
         out->next_bridge pointer has not been touched yet
         (I assume we should not touch the refcount in this case)

      b. drm_bridge_put(out->bridge): unneeded because the goto is inside
         an 'if (!out->bridge)', thus there is no reference at all to put

Do you agree with these findings?

If you do, I guess this simple patch should fix both at once (untested):

---------------------------------8<---------------------------------
@@ -31,20 +31,14 @@ int omapdss_device_init_output(struct omap_dss_device *out,
        out->bridge = bridge;

        if (local_bridge) {
-               if (!out->bridge) {
-                       ret = -EPROBE_DEFER;
-                       goto error;
-               }
+               if (!out->bridge)
+                       return -EPROBE_DEFER;

                out->next_bridge = out->bridge;
                out->bridge = drm_bridge_get(local_bridge);
        }

        return 0;
-
-error:
-       omapdss_device_cleanup_output(out);
-       return ret;
 }
---------------------------------8<---------------------------------

Can you double check this, test on hardware and if it looks correct send
that as a separate patch?

Luca

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