linux-kernel - Re: [PATCH v4 2/2] drm/mediatek: dpi/dsi: fix possible

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Date:   Thu, 23 Nov 2023 16:37:36 +0100
From:   Michael Walle <mwalle@...nel.org>
To:     Chun-Kuang Hu <chunkuang.hu@...nel.org>
Cc:     Nícolas F . R . A . Prado 
        <nfraprado@...labora.com>, Philipp Zabel <p.zabel@...gutronix.de>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Matthias Brugger <matthias.bgg@...il.com>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        "Nancy . Lin" <nancy.lin@...iatek.com>,
        Frank Wunderlich <frank-w@...lic-files.de>,
        Jitao Shi <jitao.shi@...iatek.com>,
        Stu Hsieh <stu.hsieh@...iatek.com>,
        dri-devel@...ts.freedesktop.org,
        linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        "Jason-JH.Lin" <jason-jh.lin@...iatek.com>
Subject: Re: [PATCH v4 2/2] drm/mediatek: dpi/dsi: fix possible_crtcs
 calculation

Hi,

>> > mtk_drm_find_possible_crtc_by_comp() assumed that the main path will
>> > always have the CRTC with id 0, the ext id 1 and the third id 2. This
>> > is only true if the paths are all available. But paths are optional
>> > (see
>> > also comment in mtk_drm_kms_init()), e.g. the main path might not be
>> > enabled or available at all. Then the CRTC IDs will shift one up, e.g.
>> > ext will be 0 and the third path will be 1.
>> >
>> > To fix that, dynamically calculate the IDs by the presence of the
>> > paths.
>> >
>> > While at it, make the return code a signed one and return -ENOENT if no
>> > path is found and handle the error in the callers.
>> >
>> > Fixes: 5aa8e7647676 ("drm/mediatek: dpi/dsi: Change the getting
>> > possible_crtc way")
>> > Suggested-by: Nícolas F. R. A. Prado <nfraprado@...labora.com>
>> > Signed-off-by: Michael Walle <mwalle@...nel.org>
>> > Reviewed-by: Nícolas F. R. A. Prado <nfraprado@...labora.com>
>> > Tested-by: Nícolas F. R. A. Prado <nfraprado@...labora.com>
>> 
>> Is there anything wrong with these two patches? They are now lingering
>> around for more than two months.
>> 
>> Unfortunately, patch 2/2 won't apply anymore because of commit
>> 01389b324c97 ("drm/mediatek: Add connector dynamic selection
>> capability). And I'm a bit puzzled for what the crtc_id is used
>> there because I guess it will have the same problem this patch
>> fixes.
> 
> Please base on the latest kernel version to fix.

Of course, but the question is how to fix it. Maybe Jason-JH.Lin
can help here.

In any case, please pick patch 1/2, it's independent of the second
patch and should still apply.

-michael