linux-kernel - Re: [PATCH v2 00/10] drm/panel and i2c-hid: Allow panels and touchscreens to power sequence together

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Message-ID: <jehxiy3z4aieop5qgzmlon4u76n7gvt3kc6knxhb5yqkiz3rsp@mx27m75sx43r>
Date:   Thu, 8 Jun 2023 09:17:26 +0200
From:   Maxime Ripard <mripard@...nel.org>
To:     Douglas Anderson <dianders@...omium.org>
Cc:     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>,
        dri-devel@...ts.freedesktop.org,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        linux-input@...r.kernel.org, Daniel Vetter <daniel@...ll.ch>,
        linux-kernel@...r.kernel.org, hsinyi@...gle.com,
        cros-qcom-dts-watchers@...omium.org, devicetree@...r.kernel.org,
        yangcong5@...qin.corp-partner.google.com,
        linux-arm-msm@...r.kernel.org,
        Chris Morgan <macroalpha82@...il.com>
Subject: Re: [PATCH v2 00/10] drm/panel and i2c-hid: Allow panels and
 touchscreens to power sequence together

Hi Douglas,

On Wed, Jun 07, 2023 at 02:49:22PM -0700, Douglas Anderson wrote:
> 
> The big motivation for this patch series is mostly described in the patch
> ("drm/panel: Add a way for other devices to follow panel state"), but to
> quickly summarize here: for touchscreens that are connected to a panel we
> need the ability to power sequence the two device together. This is not a
> new need, but so far we've managed to get by through a combination of
> inefficiency, added costs, or perhaps just a little bit of brokenness.
> It's time to do better. This patch series allows us to do better.
> 
> Assuming that people think this patch series looks OK, we'll have to
> figure out the right way to land it. The panel patches and i2c-hid
> patches will go through very different trees and so either we'll need
> an Ack from one side or the other or someone to create a tag for the
> other tree to pull in. This will _probably_ require the true drm-misc
> maintainers to get involved, not a lowly committer. ;-)
> 
> Version 2 of this patch series doesn't change too much. At a high level:
> * I added all the forgotten "static" to functions.
> * I've hopefully made the bindings better.
> * I've integrated into fw_devlink.
> * I cleaned up a few descriptions / comments.
> 
> This still needs someone to say that the idea looks OK or to suggest
> an alternative that solves the problems. ;-)

Thanks for working on this.

I haven't seen in any of your commit messages how the panels were
actually "packaged" together?

Do a panel model typically come together with the i2c-hid support, or is
it added at manufacture time?

If it's the latter, it's indeed a fairly loose connection and we need
your work.

If it's the former though and we don't expect a given panel reference to
always (or never) come with a touchscreen attached, I guess we can have
something much simpler with a bunch of helpers that would register a
i2c-hid device and would be called by the panel driver itself.

And then, since everything is self-contained managing the power state
becomes easier as well.

Maxime

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