[Bug 86551] Screen freezes on boot at "fb: switching to inteldrmfb from simple"

[bugzilla-daemon at bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=86551

Jani Nikula <jani.nikula at intel.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
           Assignee|intel-gfx-bugs at lists.freede |jani.nikula at intel.com
                   |sktop.org                   |

--- Comment #6 from Jani Nikula <jani.nikula at intel.com> ---
>From the lkml report:

[drm:parse_lfp_backlight] VBT backlight PWM modulation frequency 210 Hz, active
high, min brightness 255, level 255

we stumble over because of an apparent confusion over what VBT means by min
brightness. Asking the BIOS team.

Something like this should work around the issue:

diff --git a/drivers/gpu/drm/i915/intel_panel.c
b/drivers/gpu/drm/i915/intel_panel.c
index e18b3f49074c..33d14dcc1019 100644
--- a/drivers/gpu/drm/i915/intel_panel.c
+++ b/drivers/gpu/drm/i915/intel_panel.c
@@ -1098,7 +1098,7 @@ static u32 get_backlight_min_vbt(struct intel_connector
*connector)
     WARN_ON(panel->backlight.max == 0);

     /* vbt value is a coefficient in range [0..255] */
-    return scale(dev_priv->vbt.backlight.min_brightness, 0, 255,
+    return scale(dev_priv->vbt.backlight.min_brightness, 0, 512,
              0, panel->backlight.max);
 }

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