[Intel-gfx] [PATCH] drm/i915/guc: Stop using mutex while sending CTB messages

[Chris Wilson]

Quoting Michal Wajdeczko (2020-01-31 14:58:34)
> While we are always using CT "send" buffer to send request messages
> to GuC, we usually don't ask GuC to use CT "receive" buffer to send
> back response messages, since almost all returned data can fit into
> reserved bits in status dword inside CT descriptor. However, relying
> on data modifications inside CT descriptor requires use of mutex to
> allow only single CT request in flight, until we read back that status
> dword from the CT descriptor.

Q. do we need the same lock for ct_read() and ct_write()?

Could ct_read() use a lock-free ringbuffer, and then if I've read it
right, you wouldn't have any overlapping spinlock between the interrupt
handler and the rest (thus avoiding the interrupt-off).
-Chris