[PATCH 09/11] drm/nouveau: tegra: Fall back to 32-bit DMA mask without IOMMU

[Thierry Reding]

From: Thierry Reding <treding at nvidia.com>

The GPU can usually address more than 32-bit, even without being
attached to an IOMMU. However, if the GPU is not attached to an IOMMU,
it's likely that there is no IOMMU in the system, in which case any
buffers allocated by Nouveau will likely end up in a region of memory
that cannot be accessed by host1x.

Signed-off-by: Thierry Reding <treding at nvidia.com>
---
 .../drm/nouveau/nvkm/engine/device/tegra.c    | 111 +++++++++++-------
 1 file changed, 70 insertions(+), 41 deletions(-)

diff --git a/drivers/gpu/drm/nouveau/nvkm/engine/device/tegra.c b/drivers/gpu/drm/nouveau/nvkm/engine/device/tegra.c
index fc652aaa41c7..221238a2cf53 100644
--- a/drivers/gpu/drm/nouveau/nvkm/engine/device/tegra.c
+++ b/drivers/gpu/drm/nouveau/nvkm/engine/device/tegra.c
@@ -97,7 +97,7 @@ nvkm_device_tegra_power_down(struct nvkm_device_tegra *tdev)
 	return 0;
 }
 
-static void
+static int
 nvkm_device_tegra_probe_iommu(struct nvkm_device_tegra *tdev)
 {
 #if IS_ENABLED(CONFIG_IOMMU_API)
@@ -111,47 +111,65 @@ nvkm_device_tegra_probe_iommu(struct nvkm_device_tegra *tdev)
 	 * IOMMU.
 	 */
 	if (iommu_get_domain_for_dev(dev))
-		return;
+		return -ENODEV;
 
 	if (!tdev->func->iommu_bit)
-		return;
+		return -ENODEV;
+
+	if (!iommu_present(&platform_bus_type))
+		return -ENODEV;
 
 	mutex_init(&tdev->iommu.mutex);
 
-	if (iommu_present(&platform_bus_type)) {
-		tdev->iommu.domain = iommu_domain_alloc(&platform_bus_type);
-		if (!tdev->iommu.domain)
-			goto error;
+	tdev->iommu.domain = iommu_domain_alloc(&platform_bus_type);
+	if (!tdev->iommu.domain)
+		return -ENOMEM;
 
-		/*
-		 * A IOMMU is only usable if it supports page sizes smaller
-		 * or equal to the system's PAGE_SIZE, with a preference if
-		 * both are equal.
-		 */
-		pgsize_bitmap = tdev->iommu.domain->ops->pgsize_bitmap;
-		if (pgsize_bitmap & PAGE_SIZE) {
-			tdev->iommu.pgshift = PAGE_SHIFT;
-		} else {
-			tdev->iommu.pgshift = fls(pgsize_bitmap & ~PAGE_MASK);
-			if (tdev->iommu.pgshift == 0) {
-				dev_warn(dev, "unsupported IOMMU page size\n");
-				goto free_domain;
-			}
-			tdev->iommu.pgshift -= 1;
+	/*
+	 * An IOMMU is only usable if it supports page sizes smaller or equal
+	 * to the system's PAGE_SIZE, with a preference if both are equal.
+	 */
+	pgsize_bitmap = tdev->iommu.domain->ops->pgsize_bitmap;
+	if (pgsize_bitmap & PAGE_SIZE) {
+		tdev->iommu.pgshift = PAGE_SHIFT;
+	} else {
+		tdev->iommu.pgshift = fls(pgsize_bitmap & ~PAGE_MASK);
+		if (tdev->iommu.pgshift == 0) {
+			dev_warn(dev, "unsupported IOMMU page size\n");
+			ret = -ENOTSUPP;
+			goto free_domain;
 		}
 
-		ret = iommu_attach_device(tdev->iommu.domain, dev);
-		if (ret)
-			goto free_domain;
+		tdev->iommu.pgshift -= 1;
+	}
 
-		ret = nvkm_mm_init(&tdev->iommu.mm, 0, 0,
-				   (1ULL << tdev->func->iommu_bit) >>
-				   tdev->iommu.pgshift, 1);
-		if (ret)
-			goto detach_device;
+	ret = iommu_attach_device(tdev->iommu.domain, dev);
+	if (ret) {
+		dev_warn(dev, "failed to attach to IOMMU: %d\n", ret);
+		goto free_domain;
+	}
+
+	ret = nvkm_mm_init(&tdev->iommu.mm, 0, 0,
+			   (1ULL << tdev->func->iommu_bit) >>
+			   tdev->iommu.pgshift, 1);
+	if (ret) {
+		dev_warn(dev, "failed to initialize IOVA space: %d\n", ret);
+		goto detach_device;
+	}
+
+	/*
+	 * The IOMMU bit defines the upper limit of the GPU-addressable space.
+	 */
+	ret = dma_set_mask(dev, DMA_BIT_MASK(tdev->func->iommu_bit));
+	if (ret) {
+		dev_warn(dev, "failed to set DMA mask: %d\n", ret);
+		goto fini_mm;
 	}
 
-	return;
+	return 0;
+
+fini_mm:
+	nvkm_mm_fini(&tdev->iommu.mm);
 
 detach_device:
 	iommu_detach_device(tdev->iommu.domain, dev);
@@ -159,10 +177,15 @@ nvkm_device_tegra_probe_iommu(struct nvkm_device_tegra *tdev)
 free_domain:
 	iommu_domain_free(tdev->iommu.domain);
 
-error:
+	/* reset these so that the DMA API code paths are executed */
 	tdev->iommu.domain = NULL;
 	tdev->iommu.pgshift = 0;
-	dev_err(dev, "cannot initialize IOMMU MM\n");
+
+	dev_warn(dev, "cannot initialize IOMMU MM\n");
+
+	return ret;
+#else
+	return -ENOTSUPP;
 #endif
 }
 
@@ -327,14 +350,20 @@ nvkm_device_tegra_new(const struct nvkm_device_tegra_func *func,
 		goto free;
 	}
 
-	/**
-	 * The IOMMU bit defines the upper limit of the GPU-addressable space.
-	 */
-	ret = dma_set_mask(&pdev->dev, DMA_BIT_MASK(tdev->func->iommu_bit));
-	if (ret)
-		goto free;
-
-	nvkm_device_tegra_probe_iommu(tdev);
+	ret = nvkm_device_tegra_probe_iommu(tdev);
+	if (ret) {
+		/*
+		 * If we fail to set up an IOMMU, fall back to a 32-bit DMA
+		 * mask. This is not necessary for the GPU to work because it
+		 * can usually address all of system memory. However, if the
+		 * buffers allocated by Nouveau are meant to be shared with
+		 * the display controller, we need to restrict where they can
+		 * come from.
+		 */
+		ret = dma_set_mask(&pdev->dev, DMA_BIT_MASK(32));
+		if (ret)
+			goto free;
+	}
 
 	ret = nvkm_device_tegra_power_up(tdev);
 	if (ret)
-- 
2.23.0