drm/amd/display: Disable DMCUB timeout for DCN35

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: drm/amd/display: Disable DMCUB timeout for DCN35 [Why] DMCUB can intermittently take longer than expected to process commands. Old ASIC policy was to continue while logging a diagnostic error - which works fine for ASIC without IPS, but with IPS this could lead to a race condition where we attempt to access DCN state while it's inaccessible, leading to a system hang when the NIU port is not disabled or register accesses that timeout and the display configuration in an undefined state. [How] We need to investigate why these accesses take longer than expected, but for now we should disable the timeout on DCN35 to avoid this race condition. Since the waits happen only at lower interrupt levels the risk of taking too long at higher IRQ and causing a system watchdog timeout are minimal.

References

• https://git.kernel.org/stable/c/31c254c9cd4b122a10db297124f867107a696d83
• https://git.kernel.org/stable/c/7c70e60fbf4bff1123f0e8d5cb1ae71df6164d7f