In the Linux kernel, the following vulnerability has been resolved:

drm/amd/display: Refactor DMCUB enter/exit idle interface

[Why]
We can hang in place trying to send commands when the DMCUB isn't
powered on.

[How]
We need to exit out of the idle state prior to sending a command,
but the process that performs the exit also invokes a command itself.

Fixing this issue involves the following:

1. Using a software state to track whether or not we need to start
   the process to exit idle or notify idle.

It's possible for the hardware to have exited an idle state without
driver knowledge, but entering one is always restricted to a driver
allow - which makes the SW state vs HW state mismatch issue purely one
of optimization, which should seldomly be hit, if at all.

2. Refactor any instances of exit/notify idle to use a single wrapper
   that maintains this SW state.

This works simialr to dc_allow_idle_optimizations, but works at the
DMCUB level and makes sure the state is marked prior to any notify/exit
idle so we don't enter an infinite loop.

3. Make sure we exit out of idle prior to sending any commands or
   waiting for DMCUB idle.

This patch takes care of 1/2. A future patch will take care of wrapping
DMCUB command submission with calls to this new interface.

kernel.org https://git.kernel.org/stable/c/820c3870c491946a78950cdf961bf40e28c1025f [No types assigned]

kernel.org https://git.kernel.org/stable/c/8e57c06bf4b0f51a4d6958e15e1a99c9520d00fa [No types assigned]