linux-kernel - Re: [PATCH v3 02/10] drm/panel: Check for already prepared/enabled in drm

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Message-ID: <kuctj2p353nsae24lrhcymqqpfajbc7qoqly63zpwvdp6lgu3b@kk4gpzsapxnn>
Date:   Mon, 31 Jul 2023 19:03:07 +0200
From:   Maxime Ripard <mripard@...nel.org>
To:     Chris Morgan <macroalpha82@...il.com>
Cc:     Doug Anderson <dianders@...omium.org>,
        Jiri Kosina <jikos@...nel.org>,
        Benjamin Tissoires <benjamin.tissoires@...hat.com>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Sam Ravnborg <sam@...nborg.org>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        cros-qcom-dts-watchers@...omium.org, linux-input@...r.kernel.org,
        hsinyi@...gle.com, linux-arm-msm@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        devicetree@...r.kernel.org, Daniel Vetter <daniel@...ll.ch>,
        yangcong5@...qin.corp-partner.google.com
Subject: Re: [PATCH v3 02/10] drm/panel: Check for already prepared/enabled
 in drm_panel

Hi,

On Mon, Jul 31, 2023 at 11:33:22AM -0500, Chris Morgan wrote:
> In my case a few different panel drivers disable the regulators in the
> unprepare/disable routines.

And that's totally fine.

> For at least the Rockchip DSI implementations for some reason the
> panel gets unprepared more than once, which triggers an unbalanced
> regulator disable.

"For some reason" being that DW-DSI apparently finds it ok to bypass any
kind of abstraction and randomly calling panel functions by itself:

https://elixir.bootlin.com/linux/v6.4.7/source/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c#L868

It looks like it's fixed it current drm-misc-next though.

> Obviously though the correct course of action is to fix the reason why
> the panel is disabled more than once, but that's at least the root
> cause of this behavior on the few panels I've worked with.

Like I said we already have a commit on the way to fix that, so it
shouldn't be an issue anymore.

I stand by what I was saying earlier though, I think it's mostly
cargo-cult or drivers being very wrong. If anything, the DW-DSI stuff
made me even more convinced that we shouldn't even entertain that idea
:)

Maxime

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