On 07/10/2014 10:04 PM, Daniel Vetter wrote: > On Tue, Jul 08, 2014 at 05:25:59PM +0900, Alexandre Courbot wrote: >> On architectures for which access to GPU memory is non-coherent, >> caches need to be flushed and invalidated explicitly when BO control >> changes between CPU and GPU. >> >> This patch adds buffer synchronization functions which invokes the >> correct API (PCI or DMA) to ensure synchronization is effective. >> >> Based on the TTM DMA cache helper patches by Lucas Stach. >> >> Signed-off-by: Lucas Stach <dev at lynxeye.de> >> Signed-off-by: Alexandre Courbot <acourbot at nvidia.com> >> --- >> drivers/gpu/drm/nouveau/nouveau_bo.c | 56 >> +++++++++++++++++++++++++++++++++++ >> drivers/gpu/drm/nouveau/nouveau_bo.h | 2 ++ >> drivers/gpu/drm/nouveau/nouveau_gem.c | 12 ++++++++ >> 3 files changed, 70 insertions(+) >> >> diff --git a/drivers/gpu/drm/nouveau/nouveau_bo.c >> b/drivers/gpu/drm/nouveau/nouveau_bo.c >> index 67e9e8e2e2ec..47e4e8886769 100644 >> --- a/drivers/gpu/drm/nouveau/nouveau_bo.c >> +++ b/drivers/gpu/drm/nouveau/nouveau_bo.c >> @@ -402,6 +402,60 @@ nouveau_bo_unmap(struct nouveau_bo *nvbo) >> ttm_bo_kunmap(&nvbo->kmap); >> } >> >> +void >> +nouveau_bo_sync_for_device(struct nouveau_bo *nvbo) >> +{ >> + struct nouveau_drm *drm = nouveau_bdev(nvbo->bo.bdev); >> + struct nouveau_device *device = nouveau_dev(drm->dev); >> + struct ttm_dma_tt *ttm_dma = (struct ttm_dma_tt *)nvbo->bo.ttm; >> + int i; >> + >> + if (!ttm_dma) >> + return; >> + >> + if (nv_device_is_cpu_coherent(device) || nvbo->force_coherent) >> + return; > > Is the is_cpu_coherent check really required? On coherent platforms the > sync_for_foo should be a noop. It's the dma api's job to encapsulate this > knowledge so that drivers can be blissfully ignorant. The explicit > is_coherent check makes this a bit leaky. And same comment that underlying > the bus-specifics dma-mapping functions are identical.
I think you are right, the is_cpu_coherent check should not be needed here. I still think we should have separate paths for the PCI/DMA cases though, unless you can point me to a source that clearly states that the PCI API is deprecated and that DMA should be used instead.