linux-kernel - Re: [PATCH v7 00/36] drm/connector: Create HDMI Connector infrastructure

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Date: Sun, 25 Feb 2024 16:50:00 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Maxime Ripard <mripard@...nel.org>, Neil Armstrong <neil.armstrong@...aro.org>, 
	Abhinav Kumar <quic_abhinavk@...cinc.com>, freedreno <freedreno@...ts.freedesktop.org>
Cc: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
	Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>, 
	Jonathan Corbet <corbet@....net>, Sandy Huang <hjc@...k-chips.com>, Heiko Stübner <heiko@...ech.de>, 
	Chen-Yu Tsai <wens@...e.org>, Jernej Skrabec <jernej.skrabec@...il.com>, 
	Samuel Holland <samuel@...lland.org>, Hans Verkuil <hverkuil@...all.nl>, 
	Sebastian Wick <sebastian.wick@...hat.com>, 
	Ville Syrjälä <ville.syrjala@...ux.intel.com>, 
	dri-devel@...ts.freedesktop.org, linux-arm-kernel@...ts.infradead.org, 
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-media@...r.kernel.org, linux-rockchip@...ts.infradead.org, 
	linux-sunxi@...ts.linux.dev, Dave Stevenson <dave.stevenson@...pberrypi.com>, 
	Sui Jingfeng <sui.jingfeng@...ux.dev>
Subject: Re: [PATCH v7 00/36] drm/connector: Create HDMI Connector infrastructure

Hi Maxime,

On Thu, 22 Feb 2024 at 20:14, Maxime Ripard <mripard@...nel.org> wrote:
>
> Hi,
>
> Here's a series that creates some extra infrastructure specifically
> targeted at HDMI controllers.
>
> The idea behind this series came from a recent discussion on IRC during
> which we discussed infoframes generation of i915 vs everything else.
>
> Infoframes generation code still requires some decent boilerplate, with
> each driver doing some variation of it.
>
> In parallel, while working on vc4, we ended up converting a lot of i915
> logic (mostly around format / bpc selection, and scrambler setup) to
> apply on top of a driver that relies only on helpers.
>
> While currently sitting in the vc4 driver, none of that logic actually
> relies on any driver or hardware-specific behaviour.
>
> The only missing piece to make it shareable are a bunch of extra
> variables stored in a state (current bpc, format, RGB range selection,
> etc.).
>
> The initial implementation was relying on some generic subclass of
> drm_connector to address HDMI connectors, with a bunch of helpers that
> will take care of all the "HDMI Spec" related code. Scrambler setup is
> missing at the moment but can easily be plugged in.
>
> The feedback was that creating a connector subclass like was done for
> writeback would prevent the adoption of those helpers since it couldn't
> be used in all situations (like when the connector driver can implement
> multiple output) and required more churn to cast between the
> drm_connector and its subclass. The decision was thus to provide a set
> of helper and to store the required variables in drm_connector and
> drm_connector_state. This what has been implemented now.
>
> Hans Verkuil also expressed interest in implementing a mechanism in v4l2
> to retrieve infoframes from HDMI receiver and implementing a tool to
> decode (and eventually check) infoframes. His current work on
> edid-decode to enable that based on that series can be found here:
> https://git.linuxtv.org/hverkuil/edid-decode.git/log/?h=hverkuil
>
> And some more context here:
> https://lore.kernel.org/dri-devel/50db7366-cd3d-4675-aaad-b857202234de@xs4all.nl/
>
> This series thus leverages the infoframe generation code to expose it
> through debugfs.

[...]

>
> Let me know what you think,
> Maxime

The overall idea looks great. I've started checking how I can use that
for our msm devices family, which makes use of bridges and
drm_bridge_connector.
My current idea is to extend the drm_bridge_funcs with the new
callback to be called once the drm_connector has been instantiated.
This way all the bridges can influence new connector.
Another possibility is to follow drm_bridge_connector design closely
and let it call into drm_connector_hdmi code if it detects that the
last bridge is the HDMI one.
WDYT?

Some context, older MSM devices have an on-die HDMI encoder,
implemented as drm_bridge at drivers/gpu/drm/msm/hdmi. Newer
generation of devices has dropped the on-die HDMI implementation in
favour of using external DSI-to-HDMI bridges, like Lontium LT9611 or
LT9611UXC. I'm looking at enabling new HDMI infrastructure for both
cases.

-- 
With best wishes
Dmitry