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commit 7eb2c4dd54ff841f2fe509a84973eb25fa20bda2 upstream. LSPCON adapters in low-power state may ignore the first I2C write during TMDS output buffer enabling, resulting in a blank screen even with an otherwise enabled pipe. Fix this by reading back and validating the written value a few times. The problem was noticed on GLK machines with an onboard LSPCON adapter after entering/exiting DC5 power state. Doing an I2C read of the adapter ID as the first transaction - instead of the I2C write to enable the TMDS buffers - returns the correct value. Based on this we assume that the transaction itself is sent properly, it's only the adapter that is not ready for some reason to accept this first write after waking from low-power state. In my case the second I2C write attempt always succeeded. Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=105854 Cc: Clinton Taylor <clinton.a.taylor@intel.com> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com> Cc: stable@vger.kernel.org Signed-off-by: Imre Deak <imre.deak@intel.com> Signed-off-by: Jani Nikula <jani.nikula@intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20180416155309.11100-1-imre.deak@intel.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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.