linux-kernel - Re: [PATCH 1/2] drm/input_helper: Add new input-handling helper

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Message-ID: <YYW6FwSeNMK25ENm@google.com>
Date:   Fri, 5 Nov 2021 16:11:19 -0700
From:   Dmitry Torokhov <dmitry.torokhov@...il.com>
To:     Brian Norris <briannorris@...omium.org>
Cc:     Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Andrzej Hajda <andrzej.hajda@...el.com>,
        linux-kernel@...r.kernel.org, linux-input@...r.kernel.org,
        David Airlie <airlied@...ux.ie>,
        linux-rockchip@...ts.infradead.org,
        "Kristian H . Kristensen" <hoegsberg@...gle.com>,
        Doug Anderson <dianders@...omium.org>,
        Rob Clark <robdclark@...omium.org>,
        Rob Clark <robdclark@...il.com>,
        Daniel Vetter <daniel@...ll.ch>
Subject: Re: [PATCH 1/2] drm/input_helper: Add new input-handling helper

On Wed, Nov 03, 2021 at 04:40:17PM -0700, Brian Norris wrote:
> A variety of applications have found it useful to listen to
> user-initiated input events to make decisions within a DRM driver, given
> that input events are often the first sign that we're going to start
> doing latency-sensitive activities:
> 
>  * Panel self-refresh: software-directed self-refresh (e.g., with
>    Rockchip eDP) is especially latency sensitive. In some cases, it can
>    take 10s of milliseconds for a panel to exit self-refresh, which can
>    be noticeable. Rockchip RK3399 Chrome OS systems have always shipped
>    with an input_handler boost, that preemptively exits self-refresh
>    whenever there is input activity.
> 
>  * GPU drivers: on GPU-accelerated desktop systems, we may need to
>    render new frames immediately after user activity. Powering up the
>    GPU can take enough time that it is worthwhile to start this process
>    as soon as there is input activity. Many Chrome OS systems also ship
>    with an input_handler boost that powers up the GPU.
> 
> This patch provides a small helper library that abstracts some of the
> input-subsystem details around picking which devices to listen to, and
> some other boilerplate. This will be used in the next patch to implement
> the first bullet: preemptive exit for panel self-refresh.
> 
> Bits of this are adapted from code the Android and/or Chrome OS kernels
> have been carrying for a while.

If this is acceptable to DRM folks I am OK with this from input POV. The
only think I would call out that the callback is executed in atomic
context with interrupts disabled.

Acked-by: Dmitry Torokhov <dmitry.torokhov@...il.com>

Thanks.

-- 
Dmitry