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IBX has a documented workaround which states that when we disable the port we must change its transcoder select to A, otherwise it will prevent the other port (DP vs. HDMI/SDVO) from using transcoder A. We implement the workaround during encoder disable, but looks like some BIOSen leave transcoder B selected even when the port wasn't actually enabled by the BIOS. That will trip up our asserts that attempt to make sure we never forget this w/a. Sanitize the transcoder select to A for all disabled PCH DP/HDMI/SDVO ports. We assume that the port was never enabled by the BIOS on transcoder B, because if it had we'd actually have to toggle the port on and back off to properly switch it back to transcoder A. That would cause some display flicker if transcoder A is already enabled on some other port, so it's better not to do it unless absolutely necessary. Since we have no indication that the transcoder select is misbehaving on the affected machines we can assume the port was never actually enabled by the BIOS. This cures warning like this during driver load: IBX PCH DP C still using transcoder B WARNING: CPU: 2 PID: 172 at drivers/gpu/drm/i915/intel_display.c:1279 assert_pch_dp_disabled+0x9e/0xb0 [i915] v2: Add comments to remind the reader that SDVOB==HDMIB (Chris) Cc: Chris Wilson <chris@chris-wilson.co.uk> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20181108143635.9556-1-ville.syrjala@linux.intel.com Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.