> -----Original Message----- > From: Nikula, Jani > Sent: Thursday, November 20, 2014 3:59 AM > To: intel-gfx@xxxxxxxxxxxxxxxxxxxxx > Cc: Nikula, Jani; Eoff, Ullysses A > Subject: [RFC PATCH] drm/i915: avoid round-trip scaling errors in actual_brightness > > Due to scaling, the userspace and hardware brightness ranges might not > have a 1:1 mapping, causing the backlight class sysfs actual_brightness > not match the brightness attribute just written. While this is not a > strict requirement per Documentation/ABI/stable/sysfs-class-backlight, > try the userspace->hardware scaling for a match first and return the > cached value to not confuse userspace. > > The problem was already mitigated by > > commit 673e7bbdb3920b62cfc6c710bea626b0a9b0f43a > Author: U. Artie Eoff <ullysses.a.eoff@xxxxxxxxx> > Date: Mon Sep 29 15:49:32 2014 -0700 > > drm/i915: intel_backlight scale() math WA > > but this should be more robust for cases where the userspace expects > actual_brightness to match the just written brightness. > > Reference: http://mid.gmane.org/1415737838-9640-1-git-send-email-ullysses.a.eoff@xxxxxxxxx > Reference: https://bugzilla.kernel.org/show_bug.cgi?id=85861 > Cc: U. Artie Eoff <ullysses.a.eoff@xxxxxxxxx> > Signed-off-by: Jani Nikula <jani.nikula@xxxxxxxxx> Tested-by: U. Artie Eoff <ullysses.a.eoff@xxxxxxxxx> > --- > drivers/gpu/drm/i915/intel_panel.c | 12 +++++++++++- > 1 file changed, 11 insertions(+), 1 deletion(-) > > diff --git a/drivers/gpu/drm/i915/intel_panel.c b/drivers/gpu/drm/i915/intel_panel.c > index 4d63839bd9b4..675b56e105e7 100644 > --- a/drivers/gpu/drm/i915/intel_panel.c > +++ b/drivers/gpu/drm/i915/intel_panel.c > @@ -1024,7 +1024,17 @@ static int intel_backlight_device_get_brightness(struct backlight_device *bd) > drm_modeset_lock(&dev->mode_config.connection_mutex, NULL); > > hw_level = intel_panel_get_backlight(connector); > - ret = scale_hw_to_user(connector, hw_level, bd->props.max_brightness); > + > + /* > + * Check the userspace->hardware scaling for a match first to avoid > + * scaling errors in the userspace->hardware->userspace round-trip. > + */ > + if (hw_level == scale_user_to_hw(connector, bd->props.brightness, > + bd->props.max_brightness)) > + ret = bd->props.brightness; > + else > + ret = scale_hw_to_user(connector, hw_level, > + bd->props.max_brightness); > > drm_modeset_unlock(&dev->mode_config.connection_mutex); > intel_runtime_pm_put(dev_priv); > -- > 2.1.3 _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/intel-gfx
