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drm/i915/backlight: fix CPU mode backlight takeover on LPT 

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 5b1ec9ac7a
("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: 5b1ec9ac7a ("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: Lyude Paul <lyude@redhat.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210108152841.6944-1-jani.nikula@intel.com
(cherry picked from commit 0d4ced1c5b)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
master
Jani Nikula 2021-01-08 17:28:41 +02:00
parent 057fe3535e
commit bb83d5fb55
1 changed files with 5 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

9
drivers/gpu/drm/i915/display/intel_panel.c
View File

@ -1650,16 +1650,13 @@ 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);
@ -1667,6 +1664,10 @@ 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;
}