From 92714006eb4d10ddfaa0eca41c81e6b483e02f93 Mon Sep 17 00:00:00 2001 From: Gareth Yu Date: Thu, 21 Mar 2024 12:53:11 +0800 Subject: [PATCH] drm/i915/backlight: Do not bump min brightness to max on enable MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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. Cc: Tejas Upadhyay Cc: Matt Roper Cc: Ville Syrjälä Signed-off-by: Gareth Yu Reviewed-by: Jani Nikula [Jani: Rewrote the commit message.] Signed-off-by: Jani Nikula Link: https://patchwork.freedesktop.org/patch/msgid/20240321045311.2124111-1-gareth.yu@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 9e4a9d4f1585b..4d4330410b4d9 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,