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The Panel Power Sequencer lock held on an eDP port (a) blocks a DP AUX transfer on another port (b), since the PPS lock is device global, thus shared by all ports. The PPS lock can be held on port (a) for a longer period due to the various PPS delays (panel/backlight on/off, power-cycle delays). This in turn can cause an MST down-message request on port (b) time out, if the above PPS delay defers the handling of the reply to the request by more than 100ms: the MST branch device sending the reply (signaling this via the DP_DOWN_REP_MSG_RDY flag in the DP_DEVICE_SERVICE_IRQ_VECTOR DPCD register) may cancel the reply (clearing DP_DOWN_REP_MSG_RDY and the reply message buffer) after 110 ms, if the reply is not processed by that time. Avoid MST down-message timeouts described above, by locking the PPS state for AUX transfers only if this is actually required: on eDP ports, where the VDD power depends on the PPS state and on all DP and eDP ports on VLV/CHV, where the PPS is a pipe instance and hence a modeset on any port possibly affecting the PPS state. v2: Don't move PPS locking/VDD enabling to a separate function. (Jani) Cc: Jani Nikula <jani.nikula@intel.com> Reviewed-by: Jani Nikula <jani.nikula@intel.com> Signed-off-by: Imre Deak <imre.deak@intel.com> Link: https://lore.kernel.org/r/20250324180145.142884-3-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 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.