57a1b08937
Although the DisplayPort spec explicitly calls out the 1.62/2.7/5.4/8.1 link rates, the value of LINK_BW_SET is calculated. The DisplayPort spec says "Main-Link Bandwidth Setting = Value x 0.27Gbps/lane". A bridge that we're looking to upstream uses 6.75Gbps rate (value 0x19) [1], and that precludes it from using these functions. This 6.75Gbps rate is defined in the spec as (credit to Ville for posting this): A MyDP Source device, upon reading the MAX_LINK_RATE register of the downstream DPRX programmed to 19h (which can be the case only for a MyDP-to-Legacy or MyDP-to-DP lane count converter) can program the LINK_BW_SET register (DPCD Address 00100h) to 19h to enable 6.75Gbps/lane." So to avoid failing on legitimate rates in the future, this patch calculates thevalues according to spec instead of restricting these values to one of the DP_LINK_BW_* #defines. No functional change for the well-defined values, but we lose the warning (and return the correct value) for ill-defined bw values. Signed-off-by: Sean Paul <seanpaul@chromium.org> [1] https://chromium-review.googlesource.com/c/chromiumos/third_party/kernel/+/1689251/2/drivers/gpu/drm/bridge/analogix/anx7625.c#636 Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com> Signed-off-by: Sean Paul <seanpaul@chromium.org> Link: https://patchwork.freedesktop.org/patch/msgid/20190717160148.256826-1-sean@poorly.run
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.
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.