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GSP has its own state for keeping track of whether or not a given display connector is plugged in or not, and enforces this state on the driver. In particular, AUX transactions on a DisplayPort connector which GSP says is disconnected can never succeed - and can in some cases even cause unexpected timeouts, which can trickle up to cause other problems. A good example of this is runtime power management: where we can actually get stuck trying to resume the GPU if a userspace application like fwupd tries accessing a drm_aux_dev for a disconnected port. This was an issue I hit a few times with my Slimbook Executive 16 - where trying to offload something to the discrete GPU would wake it up, and then potentially cause it to timeout as fwupd tried to immediately access the dp_aux_dev nodes for nouveau. Likewise: we don't really have any cases I know of where we'd want to ignore this state and try an aux transaction anyway - and failing pointless aux transactions immediately can even speed things up. So - let's start enabling/disabling the aux bus in nouveau_dp_detect() to fix this. We enable the aux bus during connector probing, and leave it enabled if we discover something is actually on the connector. Otherwise, we just shut it off. This should fix some people's runtime PM issues (like myself), and also get rid of quite of a lot of GSP error spam in dmesg. Signed-off-by: Lyude Paul <lyude@redhat.com> Reviewed-by: Dave Airlie <airlied@redhat.com> Link: https://patchwork.freedesktop.org/patch/msgid/20240404233736.7946-2-lyude@redhat.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.