Message-ID: <9b0e99f5-554b-428f-856c-cc32f4520c73@siemens.com>
Date: Mon, 23 Sep 2024 09:42:27 +0200
From: Jan Kiszka <jan.kiszka@...mens.com>
To: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>,
 Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
 Alexander Stein <alexander.stein@...tq-group.com>
Cc: Aradhya Bhatia <a-bhatia1@...com>, dri-devel@...ts.freedesktop.org,
 Marek Vasut <marex@...x.de>, Andrzej Hajda <andrzej.hajda@...el.com>,
 Neil Armstrong <neil.armstrong@...aro.org>, Robert Foss <rfoss@...nel.org>,
 Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
 Jonas Karlman <jonas@...boo.se>, Jernej Skrabec <jernej.skrabec@...il.com>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>,
 Sam Ravnborg <sam@...nborg.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 0/2] drm/bridge: tc358767: Fix
 DRM_BRIDGE_ATTACH_NO_CONNECTOR case

On 28.08.24 15:32, Tomi Valkeinen wrote:
> On 26/08/2024 22:35, Jan Kiszka wrote:
>> On 24.06.24 12:17, Dmitry Baryshkov wrote:
>>> On Mon, 24 Jun 2024 at 13:07, Alexander Stein
>>> <alexander.stein@...tq-group.com> wrote:
>>>>
>>>> Hi,
>>>>
>>>> Am Montag, 24. Juni 2024, 11:49:04 CEST schrieb Dmitry Baryshkov:
>>>>> On Mon, Jun 24, 2024 at 03:07:10PM GMT, Aradhya Bhatia wrote:
>>>>>>
>>>>>>
>>>>>> On 22/06/24 17:49, Dmitry Baryshkov wrote:
>>>>>>> On Sat, Jun 22, 2024 at 05:16:58PM GMT, Aradhya Bhatia wrote:
>>>>>>>>
>>>>>>>>
>>>>>>>> On 17-Jun-24 13:41, Dmitry Baryshkov wrote:
>>>>>>>>> On Mon, Jun 17, 2024 at 07:40:32AM GMT, Jan Kiszka wrote:
>>>>>>>>>> On 16.02.24 15:57, Marek Vasut wrote:
>>>>>>>>>>> On 2/16/24 10:10, Tomi Valkeinen wrote:
>>>>>>>>>>>> Ok. Does anyone have a worry that these patches make the
>>>>>>>>>>>> situation
>>>>>>>>>>>> worse for the DSI case than it was before? Afaics, if the
>>>>>>>>>>>> DSI lanes
>>>>>>>>>>>> are not set up early enough by the DSI host, the driver
>>>>>>>>>>>> would break
>>>>>>>>>>>> with and without these patches.
>>>>>>>>>>>>
>>>>>>>>>>>> These do fix the driver for DRM_BRIDGE_ATTACH_NO_CONNECTOR
>>>>>>>>>>>> and DPI, so
>>>>>>>>>>>> I'd like to merge these unless these cause a regression with
>>>>>>>>>>>> the DSI
>>>>>>>>>>>> case.
>>>>>>>>>>>
>>>>>>>>>>> 1/2 looks good to me, go ahead and apply .
>>>>>>>>
>>>>>>>> Isn't there any way for the second patch to move forward as well
>>>>>>>> though?
>>>>>>>> The bridge device (under DPI to (e)DP mode) cannot really work
>>>>>>>> without
>>>>>>>> it, and the patches have been pending idle for a long time. =)
>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> My local patches still apply on top of 6.10-rc4, so I don't
>>>>>>>>>> think this
>>>>>>>>>> ever happened. What's still holding up this long-pending fix
>>>>>>>>>> (at least
>>>>>>>>>> for our devices)?
>>>>>>>>>
>>>>>>>>> Neither of the patches contains Fixes tags. If the first patch
>>>>>>>>> fixes an
>>>>>>>>> issue in previous kernels, please consider following the stable
>>>>>>>>> process.
>>>>>>>>>
>>>>>>>>> If we are unsure about the second patch, please send the first
>>>>>>>>> patch
>>>>>>>>> separately, adding proper tags.
>>>>>>>>>
>>>>>>>>
>>>>>>>> Thanks Dmitry! I can send the patches again with the required fixes
>>>>>>>> tags (or just patch-1 if we cannot do anything about patch-2).
>>>>>>>
>>>>>>> The problem with the second patch is that it get mixed reviews. I
>>>>>>> can
>>>>>>> ack the first patch, but for the second one I'd need a
>>>>>>> confirmation from
>>>>>>> somebody else. I'll go on and apply the first patch later today.
>>>>>>>
>>>>>>
>>>>>> Thanks Dmitry!
>>>>>>
>>>>>> However, would it be okay if I instead add another patch that makes 2
>>>>>> versions of the "tc_edp_bridge_funcs", say
>>>>>> "tc_dpi_edp_bridge_funcs" and
>>>>>> "tc_dsi_edp_bridge_funcs", that have all the same function hooks
>>>>>> except
>>>>>> for the .edid_read()?
>>>>>>
>>>>>> The dsi edid_read() will remain the same, and Tomi's patch - patch
>>>>>> 2/2 -
>>>>>> will only fix the dpi version of the edid_read()?
>>>>>>
>>>>>> The bridge already has the capability to distinguish a DSI input
>>>>>> from a
>>>>>> DPI input. This can be leveraged to decide which set of functions
>>>>>> need
>>>>>> to be used without any major changes.
>>>>>
>>>>> I'd prefer if somebody with the DSI setup can ack / test the second
>>>>> patch.
>>>>>
>>>>>
>>>>
>>>> Now that my DSI-DP setup works apparently without issue I could test
>>>> patch 2.
>>>> Since my setup does not use DRM_BRIDGE_ATTACH_NO_CONNECTOR (running on
>>>> drivers/gpu/drm/mxsfb/lcdif_drv.c), I can only say
>>>> there is no regression.
>>>
>>> Let me send a (non-tested) patch, switching to drm_bridge_connector,
>>> then you can probably test both of them
>>>
>>
>> I suppose [1] was that follow-up, just not leading to success, right?
>>
>> Now, what's next? I'd love to see the regression we have for the IOT2050
>> devices finally fixed, even if it now only requires a short downstream
>> patch.
>>
>> Jan
>>
>> [1]
>> https://lore.kernel.org/dri-devel/20240624-mxc-lcdif-bridge-attach-v1-1-37e8c5d5d934@linaro.org/
> 
> I have to say I don't remember the details for this anymore, but half a
> year ago I said:
> 
>> Afaics, if the DSI lanes are not set up early enough by the DSI host,
>> the driver would break with and without these patches.
> 
> I'm not sure if that is correct or not. But if it is, then, afaiu, this
> (the second patch):
> 
> - Fixes the issue for the DPI-DP use case
> 
> - Doesn't cause issues for the DSI-DP use case without
> DRM_BRIDGE_ATTACH_NO_CONNECTOR (as per Alexander's test)
> 
> - Shouldn't cause (new) issues for the DSI-DP use case with
> DRM_BRIDGE_ATTACH_NO_CONNECTOR (as per my code review and guessing...)
> 
> The third point is somewhat concerning, of course, but do we have any
> setup with DSI-DP and DRM_BRIDGE_ATTACH_NO_CONNECTOR that works now? If
> not, maybe we can just ignore the possible issues, as this fixes
> problems on a setup we do have.
> 

As Dmitry asked me during Plumbers to revalidate if our setup still
needs patch 2, I just did that over 6.11.0-next-20240923 (where patch 1
is now included). No surprise, it is still needed for our iot2050 device
series, otherwise the display remains black.

Jan

-- 
Siemens AG, Technology
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