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'Set context latency' (SCL, Window W2) is defined as the number of lines before the double buffering point, which are required to complete programming of the registers, typically when DSB is used to program the display registers. Since we are not using this window for programming the registers, this is mostly set to 0, unless there is a requirement for few cases related to PSR/PR where the 'set context latency' should be at least 1. Currently we are using the 'set context latency' (if required) implicitly by moving the vblank start by the required amount and then measuring the delay i.e. the difference between undelayed vblank start and delayed vblank start. Since our guardband matches the vblank length, this was not a problem as the difference between the undelayed vblank and delayed vblank was at the most equal to the 'set context latency' lines. However, if we want to optimize the guardband, the difference between the undelayed and the delayed vblank will be large and we cannot use this difference as the 'set context latency' lines. To make way for this optimization of guardband, formally introduce the 'set context latency' or SCL and track it as a new member `set_context_latency` of the structure intel_crtc_state. Eventually, all references of vblank delay where we mean to use set context latency will be replaced by this new `set_context_latency` member. Note: for TGL the TRANS_SET_CONTEXT_LATENCY doesn't exist to account for the SCL. However, the VBLANK_START-VACTIVE difference plays an identical role here ie. it can be used to create the SCL window ahead of the undelayed vblank. While readback since there is no specific register to read out the SCL, use the difference between vblank start and vactive to populate the new member for TGL. v2: - Use u16 for set_context_latency. (Ville) - s/vblank_delay/set_context_latency. (Ville) - Meld the changes for TGL with this change. (Ville) v3: - Update comment to clarify the TGL case. (Ville) - Fix typo in commit message. Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com> Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com> Link: https://lore.kernel.org/r/20250924141542.3122126-3-ankit.k.nautiyal@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 reStructuredText 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.