linux-kernel - Re: [PATCH] drm/bridge: Ignore -EPROBE

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Date:   Wed, 13 Oct 2021 08:48:32 +0200
From:   Andrzej Hajda <andrzej.hajda@...il.com>
To:     Guido Günther <agx@...xcpu.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:     Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Jyri Sarha <jyri.sarha@....fi>,
        Tomi Valkeinen <tomi.valkeinen@...asonboard.com>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/bridge: Ignore -EPROBE_DEFER when bridge attach fails

On 12.10.2021 22:47, Guido Günther wrote:
> Hi Laurent,
> On Tue, Oct 12, 2021 at 11:17:07PM +0300, Laurent Pinchart wrote:
>> Hi Guido,
>>
>> Thank you for the patch.
>>
>> On Tue, Oct 12, 2021 at 09:58:58PM +0200, Guido Günther wrote:
>>> Otherwise logs are filled with
>>>
>>>    [drm:drm_bridge_attach] *ERROR* failed to attach bridge /soc@...us@...00000/mipi-dsi@...0 0000 to encoder None-34: -517
>>>
>>> when the bridge isn't ready yet.
>>>
>>> Fixes: fb8d617f8fd6 ("drm/bridge: Centralize error message when bridge attach fails")
>>> Signed-off-by: Guido Günther <agx@...xcpu.org>
>>> ---
>>>   drivers/gpu/drm/drm_bridge.c | 11 ++++++-----
>>>   1 file changed, 6 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
>>> index a8ed66751c2d..f0508e85ae98 100644
>>> --- a/drivers/gpu/drm/drm_bridge.c
>>> +++ b/drivers/gpu/drm/drm_bridge.c
>>> @@ -227,14 +227,15 @@ int drm_bridge_attach(struct drm_encoder *encoder, struct drm_bridge *bridge,
>>>   	bridge->encoder = NULL;
>>>   	list_del(&bridge->chain_node);
>>>   
>>> +	if (ret != -EPROBE_DEFER) {
>>>   #ifdef CONFIG_OF
>>> -	DRM_ERROR("failed to attach bridge %pOF to encoder %s: %d\n",
>>> -		  bridge->of_node, encoder->name, ret);
>>> +		DRM_ERROR("failed to attach bridge %pOF to encoder %s: %d\n",
>>> +			  bridge->of_node, encoder->name, ret);
>>>   #else
>>> -	DRM_ERROR("failed to attach bridge to encoder %s: %d\n",
>>> -		  encoder->name, ret);
>>> +		DRM_ERROR("failed to attach bridge to encoder %s: %d\n",
>>> +			  encoder->name, ret);
>>>   #endif
>>> -
>>> +	}
>>
>> This looks fine as such, but I'm concerned about the direction it's
>> taking. Ideally, probe deferral should happen at probe time, way before
>> the bridge is attached. Doing otherwise is a step in the wrong direction
>> in my opinion, and something we'll end up regretting when we'll feel the
>> pain it inflicts.
> 
> The particular case I'm seeing this is the nwl driver probe deferrals if
> the panel bridge isn't ready (which needs a bunch of components
> (dsi, panel, backlight wrapped led, ...) and it probes fine later on so I
> wonder where you see the actual error cause? That downstream of the
> bridge isn't ready or that the display controller is already attaching
> the bridge?

So it is something wrong there, nwl should not publish bridge interface 
until it gather its resources (the panel in this case).

Regards
Andrzej


> 
> Cheers,
>   -- Guido
> 
>>
>>>   	return ret;
>>>   }
>>>   EXPORT_SYMBOL(drm_bridge_attach);
>>
>> -- 
>> Regards,
>>
>> Laurent Pinchart
>>