linux-kernel - Re: [PATCH 7/9] HID: i2c-hid: Support being a panel follower

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Message-ID: <CAD=FV=Ucn7BeWWGOOEX0ho7yH31VF-w7U60KFB8qSn4L1xn3fw@mail.gmail.com>
Date:   Wed, 24 May 2023 10:29:13 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     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>,
        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>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>
Cc:     dri-devel@...ts.freedesktop.org, linux-input@...r.kernel.org,
        Dmitry Torokhov <dmitry.torokhov@...il.com>, hsinyi@...gle.com,
        devicetree@...r.kernel.org,
        yangcong5@...qin.corp-partner.google.com,
        linux-kernel@...r.kernel.org, Daniel Vetter <daniel@...ll.ch>,
        linux-arm-msm@...r.kernel.org, cros-qcom-dts-watchers@...omium.org
Subject: Re: [PATCH 7/9] HID: i2c-hid: Support being a panel follower

Hi,

On Tue, May 23, 2023 at 12:31 PM Douglas Anderson <dianders@...omium.org> wrote:
>
> As talked about in the patch ("drm/panel: Add a way for other devices
> to follow panel state"), we really want to keep the power states of a
> touchscreen and the panel it's attached to in sync with each other. In
> that spirit, add support to i2c-hid to be a panel follower. This will
> let the i2c-hid driver get informed when the panel is powered on and
> off. From there we can match the i2c-hid device's power state to that
> of the panel.
>
> NOTE: this patch specifically _doesn't_ use pm_runtime to keep track
> of / manage the power state of the i2c-hid device, even though my
> first instinct said that would be the way to go. Specific problems
> with using pm_runtime():
> * The initial power up couldn't happen in a runtime resume function
>   since it create sub-devices and, apparently, that's not good to do
>   in your resume function.
> * Managing our power state with pm_runtime meant fighting to make the
>   right thing happen at system suspend to prevent the system from
>   trying to resume us only to suspend us again. While this might be
>   able to be solved, it added complexity.
> Overall the code without pm_runtime() ended up being smaller and
> easier to understand.
>
> Signed-off-by: Douglas Anderson <dianders@...omium.org>
> ---
>
>  drivers/hid/i2c-hid/i2c-hid-core.c | 82 +++++++++++++++++++++++++++++-
>  1 file changed, 81 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/hid/i2c-hid/i2c-hid-core.c b/drivers/hid/i2c-hid/i2c-hid-core.c
> index 34c0d98b4976..f1bb89377e8d 100644
> --- a/drivers/hid/i2c-hid/i2c-hid-core.c
> +++ b/drivers/hid/i2c-hid/i2c-hid-core.c
> @@ -38,6 +38,8 @@
>  #include <linux/mutex.h>
>  #include <asm/unaligned.h>
>
> +#include <drm/drm_panel.h>
> +
>  #include "../hid-ids.h"
>  #include "i2c-hid.h"
>
> @@ -107,6 +109,8 @@ struct i2c_hid {
>         struct mutex            reset_lock;
>
>         struct i2chid_ops       *ops;
> +       struct drm_panel_follower panel_follower;
> +       bool                    is_panel_follower;
>  };
>
>  static const struct i2c_hid_quirks {
> @@ -1058,6 +1062,34 @@ int i2c_hid_core_initial_power_up(struct i2c_hid *ihid)
>         return ret;
>  }
>
> +int i2c_hid_core_panel_prepared(struct drm_panel_follower *follower)

As pointed out by the kernel test robot, I clearly missed making
several functions "static" in this patch series. :( I'll fix that in
v2, but for now I'll hold off sending v2 to wait for additional
feedback.

-Doug