Re: [PATCH v2 4/8] drm/virtio: Improve DMA API usage for shmem BOs

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On 2022-03-14 22:42, Dmitry Osipenko wrote:
DRM API requires the DRM's driver to be backed with the device that can
be used for generic DMA operations. The VirtIO-GPU device can't perform
DMA operations if it uses PCI transport because PCI device driver creates
a virtual VirtIO-GPU device that isn't associated with the PCI. Use PCI's
GPU device for the DRM's device instead of the VirtIO-GPU device and drop
DMA-related hacks from the VirtIO-GPU driver.

Signed-off-by: Dmitry Osipenko <dmitry.osipenko@xxxxxxxxxxxxx>
---
  drivers/gpu/drm/virtio/virtgpu_drv.c    | 22 +++++++---
  drivers/gpu/drm/virtio/virtgpu_drv.h    |  5 +--
  drivers/gpu/drm/virtio/virtgpu_kms.c    |  7 ++--
  drivers/gpu/drm/virtio/virtgpu_object.c | 56 +++++--------------------
  drivers/gpu/drm/virtio/virtgpu_vq.c     | 13 +++---
  5 files changed, 37 insertions(+), 66 deletions(-)

diff --git a/drivers/gpu/drm/virtio/virtgpu_drv.c b/drivers/gpu/drm/virtio/virtgpu_drv.c
index 5f25a8d15464..8449dad3e65c 100644
--- a/drivers/gpu/drm/virtio/virtgpu_drv.c
+++ b/drivers/gpu/drm/virtio/virtgpu_drv.c
@@ -46,9 +46,9 @@ static int virtio_gpu_modeset = -1;
  MODULE_PARM_DESC(modeset, "Disable/Enable modesetting");
  module_param_named(modeset, virtio_gpu_modeset, int, 0400);
-static int virtio_gpu_pci_quirk(struct drm_device *dev, struct virtio_device *vdev)
+static int virtio_gpu_pci_quirk(struct drm_device *dev)
  {
-	struct pci_dev *pdev = to_pci_dev(vdev->dev.parent);
+	struct pci_dev *pdev = to_pci_dev(dev->dev);
  	const char *pname = dev_name(&pdev->dev);
  	bool vga = (pdev->class >> 8) == PCI_CLASS_DISPLAY_VGA;
  	char unique[20];
@@ -101,6 +101,7 @@ static int virtio_gpu_pci_quirk(struct drm_device *dev, struct virtio_device *vd
  static int virtio_gpu_probe(struct virtio_device *vdev)
  {
  	struct drm_device *dev;
+	struct device *dma_dev;
  	int ret;
if (drm_firmware_drivers_only() && virtio_gpu_modeset == -1)
@@ -109,18 +110,29 @@ static int virtio_gpu_probe(struct virtio_device *vdev)
  	if (virtio_gpu_modeset == 0)
  		return -EINVAL;
- dev = drm_dev_alloc(&driver, &vdev->dev);
+	/*
+	 * If GPU's parent is a PCI device, then we will use this PCI device
+	 * for the DRM's driver device because GPU won't have PCI's IOMMU DMA
+	 * ops in this case since GPU device is sitting on a separate (from PCI)
+	 * virtio-bus.
+	 */
+	if (!strcmp(vdev->dev.parent->bus->name, "pci"))

Nit: dev_is_pci() ?

However, what about other VirtIO transports? Wouldn't virtio-mmio with F_ACCESS_PLATFORM be in a similar situation?

Robin.

+		dma_dev = vdev->dev.parent;
+	else
+		dma_dev = &vdev->dev;
+
+	dev = drm_dev_alloc(&driver, dma_dev);
  	if (IS_ERR(dev))
  		return PTR_ERR(dev);
  	vdev->priv = dev;
if (!strcmp(vdev->dev.parent->bus->name, "pci")) {
-		ret = virtio_gpu_pci_quirk(dev, vdev);
+		ret = virtio_gpu_pci_quirk(dev);
  		if (ret)
  			goto err_free;
  	}
- ret = virtio_gpu_init(dev);
+	ret = virtio_gpu_init(vdev, dev);
  	if (ret)
  		goto err_free;
diff --git a/drivers/gpu/drm/virtio/virtgpu_drv.h b/drivers/gpu/drm/virtio/virtgpu_drv.h
index 0a194aaad419..b2d93cb12ebf 100644
--- a/drivers/gpu/drm/virtio/virtgpu_drv.h
+++ b/drivers/gpu/drm/virtio/virtgpu_drv.h
@@ -100,8 +100,6 @@ struct virtio_gpu_object {
struct virtio_gpu_object_shmem {
  	struct virtio_gpu_object base;
-	struct sg_table *pages;
-	uint32_t mapped;
  };
struct virtio_gpu_object_vram {
@@ -214,7 +212,6 @@ struct virtio_gpu_drv_cap_cache {
  };
struct virtio_gpu_device {
-	struct device *dev;
  	struct drm_device *ddev;
struct virtio_device *vdev;
@@ -282,7 +279,7 @@ extern struct drm_ioctl_desc virtio_gpu_ioctls[DRM_VIRTIO_NUM_IOCTLS];
  void virtio_gpu_create_context(struct drm_device *dev, struct drm_file *file);
/* virtgpu_kms.c */
-int virtio_gpu_init(struct drm_device *dev);
+int virtio_gpu_init(struct virtio_device *vdev, struct drm_device *dev);
  void virtio_gpu_deinit(struct drm_device *dev);
  void virtio_gpu_release(struct drm_device *dev);
  int virtio_gpu_driver_open(struct drm_device *dev, struct drm_file *file);
diff --git a/drivers/gpu/drm/virtio/virtgpu_kms.c b/drivers/gpu/drm/virtio/virtgpu_kms.c
index 3313b92db531..0d1e3eb61bee 100644
--- a/drivers/gpu/drm/virtio/virtgpu_kms.c
+++ b/drivers/gpu/drm/virtio/virtgpu_kms.c
@@ -110,7 +110,7 @@ static void virtio_gpu_get_capsets(struct virtio_gpu_device *vgdev,
  	vgdev->num_capsets = num_capsets;
  }
-int virtio_gpu_init(struct drm_device *dev)
+int virtio_gpu_init(struct virtio_device *vdev, struct drm_device *dev)
  {
  	static vq_callback_t *callbacks[] = {
  		virtio_gpu_ctrl_ack, virtio_gpu_cursor_ack
@@ -123,7 +123,7 @@ int virtio_gpu_init(struct drm_device *dev)
  	u32 num_scanouts, num_capsets;
  	int ret = 0;
- if (!virtio_has_feature(dev_to_virtio(dev->dev), VIRTIO_F_VERSION_1))
+	if (!virtio_has_feature(vdev, VIRTIO_F_VERSION_1))
  		return -ENODEV;
vgdev = kzalloc(sizeof(struct virtio_gpu_device), GFP_KERNEL);
@@ -132,8 +132,7 @@ int virtio_gpu_init(struct drm_device *dev)
vgdev->ddev = dev;
  	dev->dev_private = vgdev;
-	vgdev->vdev = dev_to_virtio(dev->dev);
-	vgdev->dev = dev->dev;
+	vgdev->vdev = vdev;
spin_lock_init(&vgdev->display_info_lock);
  	spin_lock_init(&vgdev->resource_export_lock);
diff --git a/drivers/gpu/drm/virtio/virtgpu_object.c b/drivers/gpu/drm/virtio/virtgpu_object.c
index 0b8cbb87f8d8..1964c0d8b51f 100644
--- a/drivers/gpu/drm/virtio/virtgpu_object.c
+++ b/drivers/gpu/drm/virtio/virtgpu_object.c
@@ -67,21 +67,6 @@ void virtio_gpu_cleanup_object(struct virtio_gpu_object *bo)
virtio_gpu_resource_id_put(vgdev, bo->hw_res_handle);
  	if (virtio_gpu_is_shmem(bo)) {
-		struct virtio_gpu_object_shmem *shmem = to_virtio_gpu_shmem(bo);
-
-		if (shmem->pages) {
-			if (shmem->mapped) {
-				dma_unmap_sgtable(vgdev->vdev->dev.parent,
-					     shmem->pages, DMA_TO_DEVICE, 0);
-				shmem->mapped = 0;
-			}
-
-			sg_free_table(shmem->pages);
-			kfree(shmem->pages);
-			shmem->pages = NULL;
-			drm_gem_shmem_unpin(&bo->base);
-		}
-
  		drm_gem_shmem_free(&bo->base);
  	} else if (virtio_gpu_is_vram(bo)) {
  		struct virtio_gpu_object_vram *vram = to_virtio_gpu_vram(bo);
@@ -153,37 +138,18 @@ static int virtio_gpu_object_shmem_init(struct virtio_gpu_device *vgdev,
  					unsigned int *nents)
  {
  	bool use_dma_api = !virtio_has_dma_quirk(vgdev->vdev);
-	struct virtio_gpu_object_shmem *shmem = to_virtio_gpu_shmem(bo);
  	struct scatterlist *sg;
-	int si, ret;
+	struct sg_table *pages;
+	int si;
- ret = drm_gem_shmem_pin(&bo->base);
-	if (ret < 0)
-		return -EINVAL;
-
-	/*
-	 * virtio_gpu uses drm_gem_shmem_get_sg_table instead of
-	 * drm_gem_shmem_get_pages_sgt because virtio has it's own set of
-	 * dma-ops. This is discouraged for other drivers, but should be fine
-	 * since virtio_gpu doesn't support dma-buf import from other devices.
-	 */
-	shmem->pages = drm_gem_shmem_get_sg_table(&bo->base);
-	ret = PTR_ERR(shmem->pages);
-	if (ret) {
-		drm_gem_shmem_unpin(&bo->base);
-		shmem->pages = NULL;
-		return ret;
-	}
+	pages = drm_gem_shmem_get_pages_sgt(&bo->base);
+	if (IS_ERR(pages))
+		return PTR_ERR(pages);
- if (use_dma_api) {
-		ret = dma_map_sgtable(vgdev->vdev->dev.parent,
-				      shmem->pages, DMA_TO_DEVICE, 0);
-		if (ret)
-			return ret;
-		*nents = shmem->mapped = shmem->pages->nents;
-	} else {
-		*nents = shmem->pages->orig_nents;
-	}
+	if (use_dma_api)
+		*nents = pages->nents;
+	else
+		*nents = pages->orig_nents;
*ents = kvmalloc_array(*nents,
  			       sizeof(struct virtio_gpu_mem_entry),
@@ -194,13 +160,13 @@ static int virtio_gpu_object_shmem_init(struct virtio_gpu_device *vgdev,
  	}
if (use_dma_api) {
-		for_each_sgtable_dma_sg(shmem->pages, sg, si) {
+		for_each_sgtable_dma_sg(pages, sg, si) {
  			(*ents)[si].addr = cpu_to_le64(sg_dma_address(sg));
  			(*ents)[si].length = cpu_to_le32(sg_dma_len(sg));
  			(*ents)[si].padding = 0;
  		}
  	} else {
-		for_each_sgtable_sg(shmem->pages, sg, si) {
+		for_each_sgtable_sg(pages, sg, si) {
  			(*ents)[si].addr = cpu_to_le64(sg_phys(sg));
  			(*ents)[si].length = cpu_to_le32(sg->length);
  			(*ents)[si].padding = 0;
diff --git a/drivers/gpu/drm/virtio/virtgpu_vq.c b/drivers/gpu/drm/virtio/virtgpu_vq.c
index 2edf31806b74..06566e44307d 100644
--- a/drivers/gpu/drm/virtio/virtgpu_vq.c
+++ b/drivers/gpu/drm/virtio/virtgpu_vq.c
@@ -593,11 +593,10 @@ void virtio_gpu_cmd_transfer_to_host_2d(struct virtio_gpu_device *vgdev,
  	struct virtio_gpu_transfer_to_host_2d *cmd_p;
  	struct virtio_gpu_vbuffer *vbuf;
  	bool use_dma_api = !virtio_has_dma_quirk(vgdev->vdev);
-	struct virtio_gpu_object_shmem *shmem = to_virtio_gpu_shmem(bo);
if (virtio_gpu_is_shmem(bo) && use_dma_api)
-		dma_sync_sgtable_for_device(vgdev->vdev->dev.parent,
-					    shmem->pages, DMA_TO_DEVICE);
+		dma_sync_sgtable_for_device(&vgdev->vdev->dev,
+					    bo->base.sgt, DMA_TO_DEVICE);
cmd_p = virtio_gpu_alloc_cmd(vgdev, &vbuf, sizeof(*cmd_p));
  	memset(cmd_p, 0, sizeof(*cmd_p));
@@ -1017,11 +1016,9 @@ void virtio_gpu_cmd_transfer_to_host_3d(struct virtio_gpu_device *vgdev,
  	struct virtio_gpu_vbuffer *vbuf;
  	bool use_dma_api = !virtio_has_dma_quirk(vgdev->vdev);
- if (virtio_gpu_is_shmem(bo) && use_dma_api) {
-		struct virtio_gpu_object_shmem *shmem = to_virtio_gpu_shmem(bo);
-		dma_sync_sgtable_for_device(vgdev->vdev->dev.parent,
-					    shmem->pages, DMA_TO_DEVICE);
-	}
+	if (virtio_gpu_is_shmem(bo) && use_dma_api)
+		dma_sync_sgtable_for_device(&vgdev->vdev->dev,
+					    bo->base.sgt, DMA_TO_DEVICE);
cmd_p = virtio_gpu_alloc_cmd(vgdev, &vbuf, sizeof(*cmd_p));
  	memset(cmd_p, 0, sizeof(*cmd_p));
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