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Add support for Display Port tunneling. For now this includes the support for Bandwidth Allocation Mode (BWA), leaving adding Panel Replay support for later. BWA allows using displays that share the same (Thunderbolt) link with their maximum resolution. Atm, this may not be possible due to the coarse granularity of partitioning the link BW among the displays on the link: the BW allocation policy is in a SW/FW/HW component on the link (on Thunderbolt it's the SW or FW Connection Manager), independent of the driver. This policy will set the DPRX maximum rate and lane count DPCD registers the GFX driver will see (0x00000, 0x00001, 0x02200, 0x02201) based on the available link BW. The granularity of the current BW allocation policy is coarse, based on the required link rate in the 1.62Gbs..8.1Gbps range and it may prevent using higher resolutions all together: the display connected first will get a share of the link BW which corresponds to its full DPRX capability (regardless of the actual mode it uses). A subsequent display connected will only get the remaining BW, which could be well below its full capability. BWA solves the above coarse granularity (reducing it to a 250Mbs..1Gps range) and first-come/first-served issues by letting the driver request the BW for each display on a link which reflects the actual modes the displays use. This patch adds the DRM core helper functions, while a follow-up change in the patchset takes them into use in the i915 driver. v2: - Fix prepare_to_wait vs. wake-up cond check order in allocate_tunnel_bw(). (Ville) - Move tunnel==NULL checks from callers in drivers to here. (Ville) - Avoid var inits in declaration blocks that can fail or have side-effects. (Ville) - Use u8 for driver and group IDs. (Ville) - Simplify API removing drm_dp_tunnel_get/put_untracked(). (Ville) - Reuse str_yes_no() instead of a local yes_no_chr(). (Ville) - s/drm_dp_tunnel_atomic_clear_state()/free_tunnel_state() and unexport the function. (Ville) - s/clear_tunnel_group_state()/free_group_state() and move kfree() to this function. (Ville) - Add separate group_free_bw() helper and describe what the tunnel estimated BW includes. (Ville) - Improve help text for CONFIG_DRM_DISPLAY_DP_TUNNEL. (Ville) - Add code comment explaining the purpose of DPCD reg read helpers. (Ville) - Add code comment describing the tunnel group name prefix format. (Ville) - Report the allocated BW as undetermined until the first allocation request. - Skip allocation requests matching the previous request. - Clear any stale BW request status flags before a new request. - Add missing error return check of drm_dp_tunnel_atomic_get_group_state() in drm_dp_tunnel_atomic_set_stream_bw(). - Add drm_dp_tunnel_get_allocated_bw(). - s/drm_dp_tunnel_atomic_get_tunnel_bw/drm_dp_tunnel_atomic_get_required_bw - Fix return value description in function doc of drm_dp_tunnel_detect(). - Add function documentation to all exported functions. v3: - Improve grouping of fields in drm_dp_tunnel_group struct. (Uma) - Fix validating the BW granularity DPCD reg value. (Uma) - Document return value of check_and_clear_status_change(). (Uma) - Fix resetting drm_dp_tunnel_ref::tunnel in drm_dp_tunnel_ref_put(). (Ville) - Allow for ALLOCATED_BW to change after a BWA enable/disable sequence. Cc: Ville Syrjälä <ville.syrjala@linux.intel.com> Reviewed-by: Uma Shankar <uma.shankar@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/20240226185246.1276018-2-imre.deak@intel.com |
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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.