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 5b1ec9ac7ab5
("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: 5b1ec9ac7ab5 ("drm/i915/backlight: Fix backlight takeover on LPT, v3.")
Cc: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>
Cc: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
Cc: Lyude Paul <lyude@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> # v5.1+
Signed-off-by: Jani Nikula <jani.nikula@xxxxxxxxx>
---
drivers/gpu/drm/i915/display/intel_panel.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)
diff --git a/drivers/gpu/drm/i915/display/intel_panel.c b/drivers/gpu/drm/i915/display/intel_panel.c
index 67f81ae995c4..7a4239d1c241 100644
--- a/drivers/gpu/drm/i915/display/intel_panel.c
+++ b/drivers/gpu/drm/i915/display/intel_panel.c
@@ -1649,16 +1649,13 @@ 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_dbg_kms(&dev_priv->drm,
"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);
intel_de_write(dev_priv, BLC_PWM_PCH_CTL1,
pch_ctl1 | BLM_PCH_OVERRIDE_ENABLE);
@@ -1666,6 +1663,10 @@ static int lpt_setup_backlight(struct intel_connector *connector, enum pipe unus
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;
}
--
2.20.1
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