On Thu, 21 Mar 2024, gareth...@intel.com wrote:
> From: Gareth Yu <gareth...@intel.com>
>
> Turn on the panel from zero brightness of the last state, the panel was
> set a maximum PWM in the flow. Once the panel initialization is completed,
> the backlight is restored to xero brightness. There is a flckering
> generated. This flicker happens in "Screen dimming and power off" of
> Google's design and resume from sleep. The sample of DMESG is below.
>
> (suspend)
> [53949.248875] i915 0000:00:02.0: [drm:intel_edp_backlight_off]
> [53949.452046] i915 0000:00:02.0: [drm:intel_backlight_set_pwm_level] set
> backlight PWM = 0
>
> (wakeup)
> [53986.067356] i915 0000:00:02.0: [drm:intel_edp_backlight_on]
> [53986.067367] i915 0000:00:02.0: [drm:intel_backlight_enable] pipe A
> [53986.067476] i915 0000:00:02.0: [drm:intel_backlight_set_pwm_level] set
> backlight PWM = 96000
> [53986.119766] backlight intel_backlight: PM: calling
> backlight_resume+0x0/0x7a @ 4916, parent: card0-eDP-1
> [53986.119781] backlight intel_backlight: PM: backlight_resume+0x0/0x7a
> returned 0 after 0 usecs
> [53986.220068] [drm:intel_backlight_device_update_status] updating
> intel_backlight, brightness=26321/96000
> [53986.220086] i915 0000:00:02.0: [drm:intel_panel_actually_set_backlight]
> set backlight level = 27961
>
> Set the brightness to the minimum value when the new brightness is less
> or equal to the minimum value to mitigate this flickering.
Thanks for the patch. I've pushed this to drm-intel-next, but took the
liberty to rewrite the commit message:
commit 92714006eb4d10ddfaa0eca41c81e6b483e02f93
Author: Gareth Yu <gareth...@intel.com>
Date: Thu Mar 21 12:53:11 2024 +0800
drm/i915/backlight: Do not bump min brightness to max on enable
Historically the expectation was to set brightness to max on enable, if
it was zero. However, the policy should be to preserve brightness across
disable/enable, for example the userspace might want to dim the
brightness before disable (e.g. on suspend) and gradually bring it back
up after enable (e.g. on resume). If the brightness gets bumped to max
at enable, this causes flicker as the userspace expects the brightness
to have been preserved across disable/enable.
For example:
(suspend)
[53949.248875] i915 0000:00:02.0: [drm:intel_edp_backlight_off]
[53949.452046] i915 0000:00:02.0: [drm:intel_backlight_set_pwm_level] set
backlight PWM = 0
(wakeup)
[53986.067356] i915 0000:00:02.0: [drm:intel_edp_backlight_on]
[53986.067367] i915 0000:00:02.0: [drm:intel_backlight_enable] pipe A
[53986.067476] i915 0000:00:02.0: [drm:intel_backlight_set_pwm_level] set
backlight PWM = 96000
[53986.119766] backlight intel_backlight: PM: calling
backlight_resume+0x0/0x7a @ 4916, parent: card0-eDP-1
[53986.119781] backlight intel_backlight: PM: backlight_resume+0x0/0x7a
returned 0 after 0 usecs
[53986.220068] [drm:intel_backlight_device_update_status] updating
intel_backlight, brightness=26321/96000
[53986.220086] i915 0000:00:02.0: [drm:intel_panel_actually_set_backlight]
set backlight level = 27961
Reduce the check to respecting the minimum brightness, and avoid bumping
min brightness to max on enable.
Note: It's possible there's still userspace out there that relies on the
old behaviour. It would be unfortunate, but there's really only one way
to find out.
Fingers crossed, let's hope nothing regresses.
BR,
Jani.
>
> Cc : Tejas Upadhyay <tejaskumarx.surendrakumar.upadh...@intel.com>
> Cc : Matt Roper <matthew.d.ro...@intel.com>
> Cc : Ville Syrjälä <ville.syrj...@linux.intel.com>
> Signed-off-by: Gareth Yu <gareth...@intel.com>
> ---
> drivers/gpu/drm/i915/display/intel_backlight.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_backlight.c
> b/drivers/gpu/drm/i915/display/intel_backlight.c
> index 3f3cd944a1c5..23fd011b6bfb 100644
> --- a/drivers/gpu/drm/i915/display/intel_backlight.c
> +++ b/drivers/gpu/drm/i915/display/intel_backlight.c
> @@ -761,8 +761,8 @@ static void __intel_backlight_enable(const struct
> intel_crtc_state *crtc_state,
>
> WARN_ON(panel->backlight.max == 0);
>
> - if (panel->backlight.level <= panel->backlight.min) {
> - panel->backlight.level = panel->backlight.max;
> + if (panel->backlight.level < panel->backlight.min) {
> + panel->backlight.level = panel->backlight.min;
> if (panel->backlight.device)
> panel->backlight.device->props.brightness =
> scale_hw_to_user(connector,
--
Jani Nikula, Intel
