The GPU device keeps a local copy of each ring buffers read pointer
(rptr) to avoid constant DMAs to/from host memory. This means it needs
to be periodically updated on the host side as the driver uses this to
determine how much space is left in the queue and may hang if it believe
the queue is full. For user-mode queues, this already happens when
queues are unmapped. For kernel mode queues (e.g., HIQ, KIQ) the rptr is
never updated leading to a hang.
In this patch the rptr for *all* queues is reported back to the kernel
whenever the queue reaches an empty state (rptr == wptr). Additionally
to handle PM4 queue wrap-around, the queue processing function checks if
the queue is not empty instead of rptr < wptr. This is state because the
driver fills PM4 queues with NOP packets on initialization and when wrap
around occurs.
Change-Id: Ie13a4354f82999208a75bb1eaec70513039ff30f
9e6a87e67a