From: Thomas Hellstrom thellstrom@vmware.com

The FAULT_FLAG_ALLOW_RETRY semantics is tricky and appears poorly documented. Add a comment to the TTM fault() implementation to avoid future confusion.

Cc: Christian Koenig christian.koenig@amd.com Signed-off-by: Thomas Hellstrom thellstrom@vmware.com --- v2: Incorrect email to Christian :) --- drivers/gpu/drm/ttm/ttm_bo_vm.c | 11 +++++++++++ 1 file changed, 11 insertions(+)

diff --git a/drivers/gpu/drm/ttm/ttm_bo_vm.c b/drivers/gpu/drm/ttm/ttm_bo_vm.c index a61a35e57d1c..e93b1ad7828f 100644 --- a/drivers/gpu/drm/ttm/ttm_bo_vm.c +++ b/drivers/gpu/drm/ttm/ttm_bo_vm.c @@ -125,6 +125,17 @@ static vm_fault_t ttm_bo_vm_fault(struct vm_fault *vmf) &bdev->man[bo->mem.mem_type]; struct vm_area_struct cvma;

+ /* + * FAULT_FLAG_ALLOW_RETRY indicates that the caller would like to avoid + * IO waits with the mmap_sem held. With FAULT_FLAG_RETRY_NOWAIT, + * the caller would like an early return with VM_FAULT_RETRY and the + * mmap_sem held. + * If FAULT_FLAG_RETRY_NOWAIT is not set, then we should drop the + * mmap_sem, perform the wait and return VM_FAULT_RETRY without + * holding it. We implement this for sleeping bo reservations + * where the reservation holder may be waiting for fences, and for + * fence waits. + */ if (unlikely(!dma_resv_trylock(bo->base.resv))) { if (vmf->flags & FAULT_FLAG_ALLOW_RETRY) { if (!(vmf->flags & FAULT_FLAG_RETRY_NOWAIT)) {