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Jani Nikula
9a86cda07a
Several major vendor USB-C->HDMI converters, in particular the DA200, fail to recover a 5.4 GHz 1 lane signal if the link N is greater than 0x80000. The link M and N depend on the pixel clock and link clock ratio. With current code link N exceeds 0x80000 only when link clock >= 540000 kHz. Except for the eDP intermediate link clocks, at least the four least significant bits are always zero. Just one bit shift right would be enough to bring even the DP 1.4 810000 kHz link clock under 0x80000 link N. The pixel clock for modes that require a link clock >= 540000 kHz would also have several least significant bits zero. Unless the user provides a mode with an odd pixel clock value, we can reduce the numbers to reach the goal, with no loss in precision. The DP spec even mentions sources making choices that "allow for static and relatively small Mvid and Nvid values", thus reducing the link M/N regardless of the sink in question seems justified. Everything here is based on the work and information gathered by Clint Taylor <clinton.a.taylor@intel.com>. This is just an iteration to reduce the parameters regardless of lane count, link rate, or sink. Reference: http://patchwork.freedesktop.org/patch/msgid/1490225256-11667-1-git-send-email-clinton.a.taylor@intel.com Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=93578 Tested-by: Mads <mads@ab3.no> Tested-by: PJ <foobar@pjmodos.net> Tested-by: François Guerraz <kubrick@fgv6.net> Tested-by: Lev Popov <leo@nabam.net> Tested-by: Igor Krivenko <igor.s.krivenko@gmail.com> Tested-by: Clint Taylor <clinton.a.taylor@intel.com> Reviewed-by: Clint Taylor <clinton.a.taylor@intel.com> Reviewed-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com> Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: Clint Taylor <clinton.a.taylor@intel.com> Cc: Anusha Srivatsa <anusha.srivatsa@intel.com> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Signed-off-by: Jani Nikula <jani.nikula@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1490614405-23337-1-git-send-email-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.