[Bug 59841] [IVB cpu eDP] panel is broken due to 657445fe86 (eDP bpp clamping)

[bugzilla-daemon at bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=59841

--- Comment #41 from Ulf Winkelvos <ulf at winkelvos.de> ---
Created attachment 107199
  --> https://bugzilla.kernel.org/attachment.cgi?id=107199&action=edit
never use bios provided bpp, but log the value

Booting 3.11-rc5 works fine from legacy mode. (see my previous comment) Booting
from uefi mode triggers this bug (and the very dark screen bug that was
described here too on the dell xps 13). Using the provided patch and booting
once from legacy and on uefi mode, gives the following results.

legacy mode - working without the patch:
[    1.570344] [drm:intel_dp_compute_config], BPPHACK - pipe_config->pipe_bpp:
24, dev_priv->vbt.edp_bpp: 24

uefi-mode - not working without the patch:
[    1.772969] [drm:intel_dp_compute_config], BPPHACK - pipe_config->pipe_bpp:
24, dev_priv->vbt.edp_bpp: 18

---
OT: brightness controls
3.11-rc5 seems to be the first kernel I tried, where brightness control work,
when booting in legacy mode. It does not work in UEFI mode though, that used to
work when using acpi_backlight=vendor.

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