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Commit 425faacf authored by Jani Nikula's avatar Jani Nikula Committed by Greg Kroah-Hartman
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drm/i915/backlight: fix CPU mode backlight takeover on LPT 



[ Upstream commit bb83d5fb550bb7db75b29e6342417fda2bbb691c ]

The pch_get_backlight(), lpt_get_backlight(), and lpt_set_backlight()
functions operate directly on the hardware registers. If inverting the
value is needed, using intel_panel_compute_brightness(), it should only
be done in the interface between hardware registers and
panel->backlight.level.

The CPU mode takeover code added in commit 5b1ec9ac
("drm/i915/backlight: Fix backlight takeover on LPT, v3.") reads the
hardware register and converts to panel->backlight.level correctly,
however the value written back should remain in the hardware register
"domain".

This hasn't been an issue, because GM45 machines are the only known
users of i915.invert_brightness and the brightness invert quirk, and
without one of them no conversion is made. It's likely nobody's ever hit
the problem.

Fixes: 5b1ec9ac ("drm/i915/backlight: Fix backlight takeover on LPT, v3.")
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Lyude Paul <lyude@redhat.com>
Cc: <stable@vger.kernel.org> # v5.1+
Reviewed-by: default avatarLyude Paul <lyude@redhat.com>
Signed-off-by: default avatarJani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210108152841.6944-1-jani.nikula@intel.com


(cherry picked from commit 0d4ced1c5bfe649196877d90442d4fd618e19153)
Signed-off-by: default avatarJani Nikula <jani.nikula@intel.com>
Signed-off-by: default avatarSasha Levin <sashal@kernel.org>
parent 72eb9fc8

drivers/gpu/drm/i915/display/intel_panel.c

+5 −4
Original line number Diff line number Diff line
@@ -1603,20 +1603,21 @@ static int lpt_setup_backlight(struct intel_connector *connector, enum pipe unus 
		val = pch_get_backlight(connector);

	else

		val = lpt_get_backlight(connector);

	val = intel_panel_compute_brightness(connector, val);

	panel->backlight.level = clamp(val, panel->backlight.min,

				       panel->backlight.max);



	if (cpu_mode) {

		DRM_DEBUG_KMS("CPU backlight register was enabled, switching to PCH override\n");



		/* Write converted CPU PWM value to PCH override register */

		lpt_set_backlight(connector->base.state, panel->backlight.level);

		lpt_set_backlight(connector->base.state, val);

		I915_WRITE(BLC_PWM_PCH_CTL1, pch_ctl1 | BLM_PCH_OVERRIDE_ENABLE);



		I915_WRITE(BLC_PWM_CPU_CTL2, cpu_ctl2 & ~BLM_PWM_ENABLE);

	}



	val = intel_panel_compute_brightness(connector, val);

	panel->backlight.level = clamp(val, panel->backlight.min,

				       panel->backlight.max);



	return 0;

}