linux-kernel - [RFC] drm/nouveau/ttm: Stop calling into swiotlb

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Date:   Thu, 28 Jul 2022 18:05:44 -0400
From:   Lyude Paul <lyude@...hat.com>
To:     nouveau@...ts.freedesktop.org
Cc:     Christoph Hellwig <hch@....de>, Ben Skeggs <bskeggs@...hat.com>,
        Karol Herbst <kherbst@...hat.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        dri-devel@...ts.freedesktop.org (open list:DRM DRIVER FOR NVIDIA
        GEFORCE/QUADRO GPUS), linux-kernel@...r.kernel.org (open list)
Subject: [RFC] drm/nouveau/ttm: Stop calling into swiotlb

Per the request of some of the DMA folks, some of the swiotlb helpers are
being sunset in favor of better alternatives that don't involve layer
mixing. Since it seems like we can actually replace the one thing we use
swiotlb for pretty easily, e.g. checking whether or not we are capable of
coherent allocations using is_swiotlb_active().

So, let's do this by replacing is_swiotlb_active() with our own
nouveau_drm_use_coherent_gpu_mapping() helper.

Signed-off-by: Lyude Paul <lyude@...hat.com>
Cc: Christoph Hellwig <hch@....de>
---

Hey! This is the patch that I came up with, but as the folks involved
with this thread can probably tell I'm not entirely sure this is
correct?

Also, someone more knowledgeable about mm with nouveau should probably
verify this as well

 drivers/gpu/drm/nouveau/nouveau_ttm.c | 13 ++++---------
 1 file changed, 4 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/nouveau/nouveau_ttm.c b/drivers/gpu/drm/nouveau/nouveau_ttm.c
index 85f1f5a0fe5d..ab7ccba1d601 100644
--- a/drivers/gpu/drm/nouveau/nouveau_ttm.c
+++ b/drivers/gpu/drm/nouveau/nouveau_ttm.c
@@ -24,7 +24,6 @@
  */
 
 #include <linux/limits.h>
-#include <linux/swiotlb.h>
 
 #include <drm/ttm/ttm_range_manager.h>
 
@@ -241,7 +240,6 @@ nouveau_ttm_init(struct nouveau_drm *drm)
 	struct nvkm_pci *pci = device->pci;
 	struct nvif_mmu *mmu = &drm->client.mmu;
 	struct drm_device *dev = drm->dev;
-	bool need_swiotlb = false;
 	int typei, ret;
 
 	ret = nouveau_ttm_init_host(drm, 0);
@@ -276,14 +274,11 @@ nouveau_ttm_init(struct nouveau_drm *drm)
 		drm->agp.cma = pci->agp.cma;
 	}
 
-#if IS_ENABLED(CONFIG_SWIOTLB) && IS_ENABLED(CONFIG_X86)
-	need_swiotlb = is_swiotlb_active(dev->dev);
-#endif
-
 	ret = ttm_device_init(&drm->ttm.bdev, &nouveau_bo_driver, drm->dev->dev,
-				  dev->anon_inode->i_mapping,
-				  dev->vma_offset_manager, need_swiotlb,
-				  drm->client.mmu.dmabits <= 32);
+			      dev->anon_inode->i_mapping,
+			      dev->vma_offset_manager,
+			      nouveau_drm_use_coherent_gpu_mapping(drm),
+			      drm->client.mmu.dmabits <= 32);
 	if (ret) {
 		NV_ERROR(drm, "error initialising bo driver, %d\n", ret);
 		return ret;
-- 
2.35.3