linux-kernel - Re: [PATCH v4] drm/msm/dp: make eDP panel as the first connected connector

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Date:   Wed, 6 Jul 2022 16:18:58 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     Kuogee Hsieh <quic_khsieh@...cinc.com>
Cc:     Rob Clark <robdclark@...il.com>, Sean Paul <sean@...rly.run>,
        Stephen Boyd <swboyd@...omium.org>,
        Vinod Koul <vkoul@...nel.org>, Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        Andy Gross <agross@...nel.org>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        "Abhinav Kumar (QUIC)" <quic_abhinavk@...cinc.com>,
        "Aravind Venkateswaran (QUIC)" <quic_aravindh@...cinc.com>,
        Sankeerth Billakanti <quic_sbillaka@...cinc.com>,
        freedreno <freedreno@...ts.freedesktop.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4] drm/msm/dp: make eDP panel as the first connected connector

Hi,

On Wed, Jul 6, 2022 at 12:32 PM Kuogee Hsieh <quic_khsieh@...cinc.com> wrote:
>
> Some userspace presumes that the first connected connector is the main
> display, where it's supposed to display e.g. the login screen. For
> laptops, this should be the main panel.
>
> This patch call drm_helper_move_panel_connectors_to_head() after
> drm_bridge_connector_init() to make sure eDP stay at head of
> connected connector list. This fixes unexpected corruption happen
> at eDP panel if eDP is not placed at head of connected connector
> list.
>
> Changes in v2:
> -- move drm_helper_move_panel_connectors_to_head() to
>                 dpu_kms_drm_obj_init()
>
> Changes in v4:
> -- move drm_helper_move_panel_connectors_to_head() to msm_drm_init()
>
> Signed-off-by: Kuogee Hsieh <quic_khsieh@...cinc.com>
> ---
>  drivers/gpu/drm/msm/msm_drv.c | 2 ++
>  1 file changed, 2 insertions(+)

Reviewed-by: Douglas Anderson <dianders@...omium.org>
Tested-by: Douglas Anderson <dianders@...omium.org>

NOTE: I tested this upstream with these two trees merged together:

msm-next: 1ff1da40d6fc Merge branches 'msm-next-lumag-core'...
qcom/for-next: d014f9463260 Merge branches 'arm64-for-5.20'...

...plus a revert to make things boot again [1]. I booted this on a
sc7280-herobrine running Chrome OS. When I do this, the original
reported glitching is fixed (yay) and I think we should land it.

...but I'm not convinced that all glitching is fixed by this. In
particular I've occasionally seen an underrun at bootup (blue color)
followed by a temporary glitch. With the above plus ${SUBJECT} patch I
also reliably see a glitch on my external (DP) display every time I
plug in. I don't see either on the downstream Chrome OS kernel,
though...

[1] https://lore.kernel.org/r/20220706144706.1.I48f35820bf3670d54940110462555c2d0a6d5eb2@changeid