7c838e2a9b
Per my reading of the eDP spec, DP_DPCD_DISPLAY_CONTROL_CAPABLE bit in
DP_EDP_CONFIGURATION_CAP should be set if the eDP display control
registers starting at offset DP_EDP_DPCD_REV are "enabled". Currently we
check the bit before reading the registers, and DP_EDP_DPCD_REV is the
only way to detect eDP revision.
Turns out there are (likely buggy) displays that require eDP 1.4+
features, such as supported link rates and link rate select, but do not
have the bit set. Read the display control registers
unconditionally. They are supposed to read zero anyway if they are not
supported, so there should be no harm in this.
This fixes the referenced bug by enabling the eDP version check, and
thus reading of the supported link rates. The panel in question has 0 in
DP_MAX_LINK_RATE which is only supported in eDP 1.4+. Without the
supported link rates method we default to RBR which is insufficient for
the panel native mode. As a curiosity, the panel also has a bogus value
of 0x12 in DP_EDP_DPCD_REV, but that passes our check for >= DP_EDP_14
(which is 0x03).
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=103400
Reported-and-tested-by: Nicolas P. <issun.artiste@gmail.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: stable@vger.kernel.org
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Manasi Navare <manasi.d.navare@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171026142932.17737-1-jani.nikula@intel.com
(cherry picked from commit
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README
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. 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.