Christian König christian.koenig@amd.com writes:
Am 27.04.2017 um 18:17 schrieb Nikola Pajkovsky:
This is super simple elimination of else branch and I should probably even use unlikely in
if (ring->count_dw < count_dw) {
However, amdgpu_ring_write() has similar if condition, but does not return after DRM_ERROR and it looks suspicious. On error, we still adding v to ring and keeping count_dw-- below zero.
if (ring->count_dw <= 0) DRM_ERROR("amdgpu: writing more dwords to the ring than expected!\n"); ring->ring[ring->wptr++] = v; ring->wptr &= ring->ptr_mask; ring->count_dw--;
I can obviously be totaly wrong. Hmm?
That's just choosing the lesser evil.
When we write more DW to the ring than expected it is possible (but not likely) that we override stuff on the ring buffer which is still executed by the command processor leading to a possible CP crash.
But when we completely drop the write the commands in the ring buffer will certainly be invalid and so the CP will certainly crash sooner or later.
Instead of choosing the lesser evil, is there good way to design ring buffer right way?
Please add the unlikely() as well and then send out the patch with a signed-of-by line and I will be happy to push it into our upstream branch.
Proper patch has been sent.