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The Synaptics MST hubs expose some sink EDID modes with a reduced HBLANK period, presumedly to save BW, which the hub expands before forwarding the stream to the sink. In particular a 4k mode with a standard CVT HBLANK period is exposed with either a CVT reduced blank RBv1,v2 (80, 160 pixel) or a non-CVT 56 pixel HBLANK period. The DP standard describes the above HBLANK expansion functionality, but it requires enabling this explicitly, whereas these hubs apply the expansion transparently. In some TBT docks with such a Synaptics hub (DELL WD22TB4) the above modes will work okay until DSC decompression is enabled in the hub for the given sink, but after this the same mode will not work reliably in decompressed mode. In another TBT dock (Thinkpad 40B0) the above modes will not work in uncompressed/18bpp mode (regardless of whether DSC decompression was enabled before or not). As a workaround force enable DSC for such modes. Apply the WA when the HBLANK period is 300ns or below, matching the above tested modes with a 533.25MHz dotclock and maximum 160 HBLANK pixels. OTOH DSC for these modes will only work above a certain compressed bpp threshold which depends on the link rate, so apply this limit as well in the workaround. On platforms, pipe/port configurations where DSC is not supported, for instance on ICL where DSC/MST is still work-in-progress, limit the minimum link bpp to 24. Apply the workaround only for Synaptics hubs which support the HBLANK expansion. v2: - Apply the WA whenever the HBLANK period is 300ns or below. v3: - Clarify in the commit log the failure modes of the different docks. - Handle platforms/pipe/port configurations without DSC support. Reviewed-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com> (v1) Signed-off-by: Imre Deak <imre.deak@intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20231107001505.3370108-4-imre.deak@intel.com |
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| README | ||
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.