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Until LNL, intel_dsb_wait_vblanks() used to wait for the undelayed vblank start. However, from PTL onwards, it waits for the start of the safe-window defined by the number of lines programmed in the register TRANS_SET_CONTEXT_LATENCY. This change was introduced to move the SCL window out of the vblank region, supporting modes with higher refresh rates and smaller vblanks. This change introduces a "safe window" a scanline range from (undelayed vblank - SCL) to (delayed vblank - SCL). As a result, on PTL+ platforms, the DSB wait for vblank completes exactly SCL lines earlier than the undelayed vblank start (safe window start). If the flip occurs in the active region and the push happens before the vmin decision boundary, the DSB wait fires early, and the push is sent inside this safe window. In such cases, the push bit is cleared at the delayed vblank, but our wait logic does not account for the early trigger, leading to DSB poll errors. To fix this, we add an explicit wait for the end of the safe window i.e., the scanline range from (undelayed vblank - SCL) to (delayed vblank - SCL). Once past this window, we are exactly SCL lines away from the delayed vblank, and our existing wait logic works as intended. This additional wait is only effective if the push occurs before the vmin decision boundary. If the push happens after the boundary, the hardware already guarantees we're SCL lines away from the delayed vblank, and the extra wait becomes a no-op. v2: - Use helpers for safe window start/end. (Ville) - Move the extra wait inside the helper to wait for delayed vblank. (Ville) - Update the commit message. v3: - Add more documentation for explanation for the wait. (Ville) - Rename intel_vrr_vmin_safe_window_start/end as this is vmin safe window. (Ville) - Minor refactoring to align with the code. (Ville) - Update the commit message for more clarity. v4: - Retain name for intel_vrr_safe_window_start as it doesn't change with vmin/vmax etc. (Ville) 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/20250924141542.3122126-7-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.