From: Jani Nikula jani.nikula@intel.com
commit bb83d5fb550bb7db75b29e6342417fda2bbb691c upstream.
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@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.nik... (cherry picked from commit 0d4ced1c5bfe649196877d90442d4fd618e19153) Signed-off-by: Jani Nikula jani.nikula@intel.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- drivers/gpu/drm/i915/display/intel_panel.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-)
--- a/drivers/gpu/drm/i915/display/intel_panel.c +++ b/drivers/gpu/drm/i915/display/intel_panel.c @@ -1650,16 +1650,13 @@ static int lpt_setup_backlight(struct in 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 in 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; }