virtio: allow caller to override device DMA mask in vp_modern

To add a bit of vendor flexibility with various virtio based devices,
allow the caller to specify a different DMA mask. This adds a dma_mask
field to struct virtio_pci_modern_device. If defined by the driver,
this mask will be used in a call to dma_set_mask_and_coherent() instead
of the traditional DMA_BIT_MASK(64). This allows limiting the DMA space
on vendor devices with address limitations.

Signed-off-by: Shannon Nelson <[e-mail]>
Acked-by: Jason Wang <[e-mail]>
Message-Id: <[e-mail]>
Signed-off-by: Michael S. Tsirkin <[e-mail]>

drivers/virtio/virtio_pci_modern_dev.c

···
 		return -EINVAL;
 	}
 
-	err = dma_set_mask_and_coherent(&pci_dev->dev, DMA_BIT_MASK(64));
+	err = dma_set_mask_and_coherent(&pci_dev->dev,
+					mdev->dma_mask ? : DMA_BIT_MASK(64));
 	if (err)
 		err = dma_set_mask_and_coherent(&pci_dev->dev,
 						DMA_BIT_MASK(32));

include/linux/virtio_pci_modern.h

···
 
 	/* optional check for vendor virtio device, returns dev_id or -ERRNO */
 	int (*device_id_check)(struct pci_dev *pdev);
+
+	/* optional mask for devices with limited DMA space */
+	u64 dma_mask;
 };
 
 /*