linux-kernel - Re: [PATCH] Revert "drm/bridge: lt9611: Do not generate HFP/HBP/HSA and EOT packet"

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Date:   Wed, 2 Aug 2023 19:31:29 +0200
From:   Marek Vasut <marex@...x.de>
To:     neil.armstrong@...aro.org, Andrzej Hajda <andrzej.hajda@...el.com>,
        Robert Foss <rfoss@...nel.org>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Jonas Karlman <jonas@...boo.se>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>
Cc:     dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Jagan Teki <jagan@...rulasolutions.com>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Amit Pundir <amit.pundir@...aro.org>
Subject: Re: [PATCH] Revert "drm/bridge: lt9611: Do not generate HFP/HBP/HSA
 and EOT packet"

On 8/2/23 14:37, Neil Armstrong wrote:
> On 02/08/2023 14:28, Marek Vasut wrote:
>> On 8/2/23 14:07, Marek Vasut wrote:
>>> On 8/2/23 10:52, Neil Armstrong wrote:
>>>> This reverts commit [1] to fix display regression on the Dragonboard 
>>>> 845c
>>>> (SDM845) devboard.
>>>>
>>>> There's a mismatch on the real action of the following flags:
>>>> - MIPI_DSI_MODE_VIDEO_NO_HSA
>>>> - MIPI_DSI_MODE_VIDEO_NO_HFP
>>>> - MIPI_DSI_MODE_VIDEO_NO_HBP
>>>> which leads to a non-working display on qcom platforms.
>>>>
>>>> [1] 8ddce13ae696 ("drm/bridge: lt9611: Do not generate HFP/HBP/HSA 
>>>> and EOT packet")
>>>>
>>>> Cc: Marek Vasut <marex@...x.de>
>>>> Cc: Robert Foss <rfoss@...nel.org>
>>>> Cc: Jagan Teki <jagan@...rulasolutions.com>
>>>> Cc: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
>>>> Cc: Abhinav Kumar <quic_abhinavk@...cinc.com>
>>>> Fixes: 8ddce13ae69 ("drm/bridge: lt9611: Do not generate HFP/HBP/HSA 
>>>> and EOT packet")
>>>> Reported-by: Amit Pundir <amit.pundir@...aro.org>
>>>> Link: 
>>>> https://lore.kernel.org/r/CAMi1Hd0TD=2z_=bcDrht3H_wiLvAFcv8Z-U_r_KUOoeMc6UMjw@mail.gmail.com/
>>>> Signed-off-by: Neil Armstrong <neil.armstrong@...aro.org>
>>>
>>> This breaks LT9611 operation on i.MX8M Mini/Nano/Plus, so, NAK.
>>>
>>> I am currently using this LT9611 with Linux 6.1.y
>>
>> Correction, 6.1.y only with the DSIM patches backported.
> 
> Well you'll need to keep [1] backported on your downstream branch,
> this revert won't propagate to v6.1 stable anyway.

I will still have a problem with those MX8M boards during my development 
on linux-next, so that isn't helping.

>>> in production and this is not acceptable. I also believe the correct 
>>> fix is on the MSM side, not on the LT9611 driver side, since MSM 
>>> incorrectly implements these flags.
>>
> 
> Since [1] breaks Qcom boards on v6.5, and [1] was added for v6.5 to make 
> the bridge work
> on i.MX8M Mini/Nano/Plus, it's not acceptable either to keep it for the 
> v6.5 release.

So, we need to find a solution which works for both, I proposed one already.