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Ever since we've parsed VBT child devices, starting from6acab15a7b("drm/i915: use the HDMI DDI buffer translations from VBT"), we've ignored the child device information if more than one child device references the same port. The rationale for this seems lost in time. Since commit311a20949f("drm/i915: don't init DP or HDMI when not supported by DDI port") we started using this information more to skip HDMI/DP init if the port wasn't there per VBT child devices. However, at the same time it added port defaults without further explanation. Thus, if the child device info was skipped due to multiple child devices referencing the same port, the device info would be retrieved from the somewhat arbitrary defaults. Finally, when commitbb1d132935("drm/i915/vbt: split out defaults that are set when there is no VBT") stopped initializing the defaults whenever VBT is present, thus trusting the VBT more, we stopped initializing ports which were referenced by more than one child device. Apparently at least Asus UX305UA, UX305U, and UX306U laptops have VBT child device blocks which cause this behaviour. Arguably they were shipped with a broken VBT. Relax the rules for multiple references to the same port, and use the first child device info to reference a port. Retain the logic to debug log about this, though. Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=101745 Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=196233 Fixes:bb1d132935("drm/i915/vbt: split out defaults that are set when there is no VBT") Tested-by: Oliver Weißbarth <mail@oweissbarth.de> Reported-by: Oliver Weißbarth <mail@oweissbarth.de> Reported-by: Didier G <didierg-divers@orange.fr> Reported-by: Giles Anderson <agander@gmail.com> Cc: Manasi Navare <manasi.d.navare@intel.com> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com> Cc: Paulo Zanoni <paulo.r.zanoni@intel.com> Cc: <stable@vger.kernel.org> # v4.12+ Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com> Signed-off-by: Jani Nikula <jani.nikula@intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20170811113907.6716-1-jani.nikula@intel.com Signed-off-by: Jani Nikula <jani.nikula@intel.com>
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.