drm/virtio: Improve DMA API usage for shmem BOs

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@collabora.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20220630200726.1884320-8-dmitry.osipenko@collabora.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

1 files changed, 12 insertions, 39 deletions

diff --git a/drivers/gpu/drm/virtio/virtgpu_drv.c b/drivers/gpu/drm/virtio/virtgpu_drv.c
index 5f25a8d15464..0141b7df97ec 100644
--- a/drivers/gpu/drm/virtio/virtgpu_drv.c
+++ b/drivers/gpu/drm/virtio/virtgpu_drv.c
@@ -46,12 +46,11 @@ 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];
 	int ret;
 
 	DRM_INFO("pci: %s detected at %s\n",
@@ -63,39 +62,7 @@ static int virtio_gpu_pci_quirk(struct drm_device *dev, struct virtio_device *vd
 			return ret;
 	}
 
-	/*
-	 * Normally the drm_dev_set_unique() call is done by core DRM.
-	 * The following comment covers, why virtio cannot rely on it.
-	 *
-	 * Unlike the other virtual GPU drivers, virtio abstracts the
-	 * underlying bus type by using struct virtio_device.
-	 *
-	 * Hence the dev_is_pci() check, used in core DRM, will fail
-	 * and the unique returned will be the virtio_device "virtio0",
-	 * while a "pci:..." one is required.
-	 *
-	 * A few other ideas were considered:
-	 * - Extend the dev_is_pci() check [in drm_set_busid] to
-	 *   consider virtio.
-	 *   Seems like a bigger hack than what we have already.
-	 *
-	 * - Point drm_device::dev to the parent of the virtio_device
-	 *   Semantic changes:
-	 *   * Using the wrong device for i2c, framebuffer_alloc and
-	 *     prime import.
-	 *   Visual changes:
-	 *   * Helpers such as DRM_DEV_ERROR, dev_info, drm_printer,
-	 *     will print the wrong information.
-	 *
-	 * We could address the latter issues, by introducing
-	 * drm_device::bus_dev, ... which would be used solely for this.
-	 *
-	 * So for the moment keep things as-is, with a bulky comment
-	 * for the next person who feels like removing this
-	 * drm_dev_set_unique() quirk.
-	 */
-	snprintf(unique, sizeof(unique), "pci:%s", pname);
-	return drm_dev_set_unique(dev, unique);
+	return 0;
 }
 
 static int virtio_gpu_probe(struct virtio_device *vdev)
@@ -109,18 +76,24 @@ static int virtio_gpu_probe(struct virtio_device *vdev)
 	if (virtio_gpu_modeset == 0)
 		return -EINVAL;
 
-	dev = drm_dev_alloc(&driver, &vdev->dev);
+	/*
+	 * The virtio-gpu device is a virtual device that doesn't have DMA
+	 * ops assigned to it, nor DMA mask set and etc. Its parent device
+	 * is actual GPU device we want to use it for the DRM's device in
+	 * order to benefit from using generic DRM APIs.
+	 */
+	dev = drm_dev_alloc(&driver, vdev->dev.parent);
 	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;