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From:   Doug Anderson <dianders@chromium.org>
Date:   Thu, 9 Jul 2020 18:38:31 -0700
Message-ID: <CAD=FV=X3oazamoKR1jHoXm-yCAp9208ahNd8y+NDPt1pU=5xRg@mail.gmail.com>
Subject: Re: [PATCH v3 6/9] drm/bridge: ti-sn65dsi86: Use 18-bit DP if we can
To:     steev@kali.org
Cc:     Laurent Pinchart <Laurent.pinchart@ideasonboard.com>,
        Andrzej Hajda <a.hajda@samsung.com>,
        David Airlie <airlied@linux.ie>,
        Bjorn Andersson <bjorn.andersson@linaro.org>,
        Daniel Vetter <daniel@ffwll.ch>,
        dri-devel <dri-devel@lists.freedesktop.org>,
        Jeffrey Hugo <jeffrey.l.hugo@gmail.com>,
        Jernej Skrabec <jernej.skrabec@siol.net>,
        Jonas Karlman <jonas@kwiboo.se>,
        linux-arm-msm <linux-arm-msm@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Neil Armstrong <narmstrong@baylibre.com>,
        Rob Clark <robdclark@chromium.org>,
        Rob Clark <robdclark@gmail.com>,
        Sean Paul <seanpaul@chromium.org>,
        Steev Klimaszewski <steev@gentoo.org>
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Hi,

On Thu, Jul 9, 2020 at 6:19 PM Steev Klimaszewski <steev@gentoo.org> wrote:
>
> Hi Doug,
>
> I've been testing 5.8 and linux-next on the Lenovo Yoga C630, and with this patch applied, there is really bad banding on the display.
>
> I'm really bad at explaining it, but you can see the differences in the following:
>
> 24bit (pre-5.8) - https://dev.gentoo.org/~steev/files/image0.jpg
>
> 18bit (5.8/linux-next) - https://dev.gentoo.org/~steev/files/image1.jpg

Presumably this means that your panel is defined improperly?  If the
panel reports that it's a 6 bits per pixel panel but it's actually an
8 bits per pixel panel then you'll run into this problem.

I would have to assume you have a bunch of out of tree patches to
support your hardware since I don't see any device trees in linuxnext
(other than cheza) that use this bridge chip.  Otherwise I could try
to check and confirm that was the problem.

-Doug