Not all architectures guarantee that uncached read will flush the write combining buffer. So marking it explicitly is recommended [1].
However we know the architecture we are operating on and can avoid wmb as the UC store will flush the wcb [2]. Omit the wmb() before invalidate as redudant. v2: squash combining and removal (Chris) v3: remove obsolete comments about posting reads (Chris) References: http://yarchive.net/comp/linux/write_combining.html [1] References: http://download.intel.com/design/PentiumII/applnots/24442201.pdf [2] Cc: Chris Wilson <ch...@chris-wilson.co.uk> Cc: Matthew Auld <matthew.a...@intel.com> Signed-off-by: Mika Kuoppala <mika.kuopp...@linux.intel.com> Reviewed-by: Chris Wilson <ch...@chris-wilson.co.uk> --- drivers/gpu/drm/i915/i915_gem_gtt.c | 18 ++++++++---------- 1 file changed, 8 insertions(+), 10 deletions(-) diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c index c879bfd9294f..6eae9e1ed8be 100644 --- a/drivers/gpu/drm/i915/i915_gem_gtt.c +++ b/drivers/gpu/drm/i915/i915_gem_gtt.c @@ -110,7 +110,8 @@ i915_get_ggtt_vma_pages(struct i915_vma *vma); static void gen6_ggtt_invalidate(struct drm_i915_private *dev_priv) { - /* Note that as an uncached mmio write, this should flush the + /* + * Note that as an uncached mmio write, this will flush the * WCB of the writes into the GGTT before it triggers the invalidate. */ I915_WRITE(GFX_FLSH_CNTL_GEN6, GFX_FLSH_CNTL_EN); @@ -2418,11 +2419,9 @@ static void gen8_ggtt_insert_entries(struct i915_address_space *vm, for_each_sgt_dma(addr, sgt_iter, vma->pages) gen8_set_pte(gtt_entries++, pte_encode | addr); - wmb(); - - /* This next bit makes the above posting read even more important. We - * want to flush the TLBs only after we're certain all the PTE updates - * have finished. + /* + * We want to flush the TLBs only after we're certain all the PTE + * updates have finished. */ ggtt->invalidate(vm->i915); } @@ -2460,11 +2459,10 @@ static void gen6_ggtt_insert_entries(struct i915_address_space *vm, dma_addr_t addr; for_each_sgt_dma(addr, iter, vma->pages) iowrite32(vm->pte_encode(addr, level, flags), &entries[i++]); - wmb(); - /* This next bit makes the above posting read even more important. We - * want to flush the TLBs only after we're certain all the PTE updates - * have finished. + /* + * We want to flush the TLBs only after we're certain all the PTE + * updates have finished. */ ggtt->invalidate(vm->i915); } -- 2.14.1 _______________________________________________ Intel-gfx mailing list Intel-gfx@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/intel-gfx
