drm/amd/display: prevent hang on link training fail

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: drm/amd/display: prevent hang on link training fail [Why] When link training fails, the phy clock will be disabled. However, in enable_streams, it is assumed that link training succeeded and the mux selects the phy clock, causing a hang when a register write is made. [How] When enable_stream is hit, check if link training failed. If it did, fall back to the ref clock to avoid a hang and keep the system in a recoverable state.

References

• https://git.kernel.org/stable/c/0363c03672cd3191f037905bf981eb523a3b71b1
• https://git.kernel.org/stable/c/04bf4f2a497e9877c425c5124652e61fb8a1a0aa
• https://git.kernel.org/stable/c/8058061ed9d6bc259d1e678607b07d259342c08f