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From:   Linus Walleij <linus.walleij@linaro.org>
Date:   Sat, 22 May 2021 12:34:28 +0200
Message-ID: <CACRpkda_MTBrXR-as5t_Ji8mU4=95NQ_GTDtjcERncm9yS1moA@mail.gmail.com>
Subject: Re: [PATCH v7 04/10] drm: Introduce the DP AUX bus
To:     Douglas Anderson <dianders@chromium.org>
Cc:     Andrzej Hajda <a.hajda@samsung.com>,
        Neil Armstrong <narmstrong@baylibre.com>,
        Laurent Pinchart <Laurent.pinchart@ideasonboard.com>,
        Jonas Karlman <jonas@kwiboo.se>,
        Jernej Skrabec <jernej.skrabec@siol.net>,
        Sam Ravnborg <sam@ravnborg.org>,
        Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>,
        Lyude Paul <lyude@redhat.com>,
        Thierry Reding <treding@nvidia.com>,
        Stephen Boyd <swboyd@chromium.org>,
        Bjorn Andersson <bjorn.andersson@linaro.org>,
        MSM <linux-arm-msm@vger.kernel.org>,
        Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        "open list:DRM PANEL DRIVERS" <dri-devel@lists.freedesktop.org>,
        Rob Clark <robdclark@chromium.org>,
        Steev Klimaszewski <steev@kali.org>,
        Rajeev Nandan <rajeevny@codeaurora.org>,
        Daniel Vetter <daniel@ffwll.ch>,
        David Airlie <airlied@linux.ie>,
        Maxime Ripard <mripard@kernel.org>,
        Thomas Zimmermann <tzimmermann@suse.de>,
        linux-kernel <linux-kernel@vger.kernel.org>
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On Mon, May 17, 2021 at 10:09 PM Douglas Anderson <dianders@chromium.org> wrote:

> Historically "simple" eDP panels have been handled by panel-simple
> which is a basic platform_device. In the device tree, the panel node
> was at the top level and not connected to anything else.
>
> Let's change it so that, instead, panels can be represented as being
> children of the "DP AUX bus". Essentially we're saying that the
> hierarchy that we're going to represent is the "control" connections
> between devices. The DP AUX bus is a control bus provided by an eDP
> controller (the parent) and consumed by a device like a panel (the
> child).
>
> The primary incentive here is to cleanly provide the panel driver the
> ability to communicate over the AUX bus while handling lifetime issues
> properly. The panel driver may want the AUX bus for controlling the
> backlight or querying the panel's EDID.
>
> The idea for this bus's design was hashed out over IRC [1].
>
> [1] https://people.freedesktop.org/~cbrill/dri-log/?channel=dri-devel&date=2021-05-11
>
> Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> Cc: Lyude Paul <lyude@redhat.com>
> Cc: Rajeev Nandan <rajeevny@codeaurora.org>
> Suggested-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> Signed-off-by: Douglas Anderson <dianders@chromium.org>

I like the concept and the general idea behind this, clean and
helpful design.
Acked-by: Linus Walleij <linus.walleij@linaro.org>

Yours,
Linus Walleij