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The DP Standard's recommendation is to use the LTTPR non-transparent mode link training if LTTPRs are detected, so let's do this. Besides power-saving, the advantages of this are that the maximum number of LTTPRs can only be used in non-transparent mode (the limit is 5-8 in transparent mode), and it provides a way to narrow down the reason for a link training failure to a given link segment. Non-transparent mode is probably also the mode that was tested the most by the industry. The changes in this patchset: - Pass the DP PHY that is currently link trained to all LT helpers, so that these can access the correct LTTPR/DPRX DPCD registers. - During LT take into account the LTTPR common lane rate/count and the per LTTPR-PHY vswing/pre-emph limits. - Switch to LTTPR non-transparent LT mode and train each link segment according to the sequence in DP Standard v2.0 (complete CR/EQ for each segment before continuing with the next segment). v2: - Switch to non-transparent mode during connector detection, which is required before reading the per-PHY LTTPR capabilities. - Move the DP_PHY_LTTPR() macro to drm_dp_helper.h (Ville) - Use the new drm_dp_dpcd_read_phy_link_status() instead of adding the same logic to intel_dp_get_link_status(). (Ville) - Make intel_dp_lttpr_phy_caps() return a pointer to the whole array instead of a pointer to its first element. (Ville) - Add the intel_dp_phy_is_downstream_of_source() helper. (Ville) - Add a code comment about the disable->enable quirk of non-transparent mode. - Add the intel_dp_training_pattern_set_reg() helper. - Fix checkpatch/sparse warns. Cc: Ville Syrjälä <ville.syrjala@linux.intel.com> Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com> Signed-off-by: Imre Deak <imre.deak@intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20201007170917.1764556-7-imre.deak@intel.com
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.