[PATCH v2 0/2] drm: Support input-boosted panel self-refresh exit

Brian Norris briannorris at chromium.org
Wed Nov 17 14:48:39 PST 2021

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.

I implement the first bullet in this series, and I also compared with
some out-of-tree patches for the second, to ensure this could be useful
there too.

Past work on upstreaming a variety of Chromebook display patches got
held up for this particular feature, as there was some desire to make it
a bit more generic, for one. See the latest here:

  [PATCH v6 24/30] drm/rockchip: Disable PSR on input events

I significantly rewrote this to adapt it to the new common
drm_self_refresh_helpers and to add a new drm_input_helper thin library,
so I only carry my own authorship on this series.

Admittedly, this "drm_input_helper" library is barely DRM-specific at
all, except that all display- and GPU-related input-watchers are likely
to want to watch similar device behavior (unlike, say, rfkill or led
input_handler code). The approximate consensus so far seems to be that
(a) this isn't much code; if we need it for other subsystems (like,
    cpufreq-boost), it's easy to implement similar logic
(b) input subsystem maintainers think the existing input_handler
    abstraction is good enough
So, I keep the thin input helper in drivers/gpu/drm/.

v1: https://lore.kernel.org/all/20211103234018.4009771-1-briannorris@chromium.org/

Changes in v2:
 - Honor CONFIG_INPUT dependency, via new CONFIG_DRM_INPUT_HELPER
 - Remove void*; users should use container_of()
 - Document the callback context
 - Delay PSR re-entry, when already disabled
 - Allow default configuration via Kconfig and modparam
 - really CC dri-devel at lists.freedesktop.org (oops!)

Brian Norris (2):
  drm/input_helper: Add new input-handling helper
  drm/self_refresh: Disable self-refresh on input events

 drivers/gpu/drm/Kconfig                   |  22 ++++
 drivers/gpu/drm/Makefile                  |   2 +
 drivers/gpu/drm/drm_input_helper.c        | 143 ++++++++++++++++++++++
 drivers/gpu/drm/drm_self_refresh_helper.c |  98 ++++++++++++---
 include/drm/drm_input_helper.h            |  41 +++++++
 5 files changed, 292 insertions(+), 14 deletions(-)
 create mode 100644 drivers/gpu/drm/drm_input_helper.c
 create mode 100644 include/drm/drm_input_helper.h


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