Hi,
From a user-space point-of-view, we discussed about this patch on IRC a few
days ago [1]. Since this adds a policy decision we think it'd be best to allow user-space to control this behavior.
Also cc Pekka.
Thanks,
Simon
[1]: https://oftc.irclog.whitequark.org/dri-devel/2021-11-07#1636276286-163627374...;
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:
https://lore.kernel.org/all/20180405095000.9756-25-enric.balletbo@collabora.... [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.or...
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@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
-- 2.34.0.rc1.387.gb447b232ab-goog