xen/virtio: Optimize the setup of "xen-grant-dma" devices

This is needed to avoid having to parse the same device-tree
several times for a given device.

For this to work we need to install the xen_virtio_restricted_mem_acc
callback in Arm's xen_guest_init() which is same callback as x86's
PV and HVM modes already use and remove the manual assignment in
xen_setup_dma_ops(). Also we need to split the code to initialize
backend_domid into a separate function.

Prior to current patch we parsed the device-tree three times:
1. xen_setup_dma_ops()->...->xen_is_dt_grant_dma_device()
2. xen_setup_dma_ops()->...->xen_dt_grant_init_backend_domid()
3. xen_virtio_mem_acc()->...->xen_is_dt_grant_dma_device()

With current patch we parse the device-tree only once in
xen_virtio_restricted_mem_acc()->...->xen_dt_grant_init_backend_domid()

Other benefits are:
- Not diverge from x86 when setting up Xen grant DMA ops
- Drop several global functions

Signed-off-by: Oleksandr Tyshchenko <[e-mail]>
Reviewed-by: Xenia Ragiadakou <[e-mail]>
Reviewed-by: Stefano Stabellini <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Juergen Gross <[e-mail]>

arch/arm/xen/enlighten.c

···
 		return 0;
 
 	if (IS_ENABLED(CONFIG_XEN_VIRTIO))
-		virtio_set_mem_acc_cb(xen_virtio_mem_acc);
+		virtio_set_mem_acc_cb(xen_virtio_restricted_mem_acc);
 
 	if (!acpi_disabled)
 		xen_acpi_guest_init();

drivers/xen/grant-dma-ops.c

···
 	.dma_supported = xen_grant_dma_supported,
 };
 
-static bool xen_is_dt_grant_dma_device(struct device *dev)
-{
-	struct device_node *iommu_np;
-	bool has_iommu;
-
-	iommu_np = of_parse_phandle(dev->of_node, "iommus", 0);
-	has_iommu = iommu_np &&
-		    of_device_is_compatible(iommu_np, "xen,grant-dma");
-	of_node_put(iommu_np);
-
-	return has_iommu;
-}
-
-bool xen_is_grant_dma_device(struct device *dev)
-{
-	/* XXX Handle only DT devices for now */
-	if (dev->of_node)
-		return xen_is_dt_grant_dma_device(dev);
-
-	return false;
-}
-
-bool xen_virtio_mem_acc(struct virtio_device *dev)
-{
-	if (IS_ENABLED(CONFIG_XEN_VIRTIO_FORCE_GRANT) || xen_pv_domain())
-		return true;
-
-	return xen_is_grant_dma_device(dev->dev.parent);
-}
-
 static int xen_dt_grant_init_backend_domid(struct device *dev,
-					   struct xen_grant_dma_data *data)
+					   domid_t *backend_domid)
 {
 	struct of_phandle_args iommu_spec;
 
 	if (of_parse_phandle_with_args(dev->of_node, "iommus", "#iommu-cells",
 			0, &iommu_spec)) {
-		dev_err(dev, "Cannot parse iommus property\n");
+		dev_dbg(dev, "Cannot parse iommus property\n");
 		return -ESRCH;
 	}
 
 	if (!of_device_is_compatible(iommu_spec.np, "xen,grant-dma") ||
 			iommu_spec.args_count != 1) {
-		dev_err(dev, "Incompatible IOMMU node\n");
+		dev_dbg(dev, "Incompatible IOMMU node\n");
 		of_node_put(iommu_spec.np);
 		return -ESRCH;
 	}
···
 	 * The endpoint ID here means the ID of the domain where the
 	 * corresponding backend is running
 	 */
-	data->backend_domid = iommu_spec.args[0];
+	*backend_domid = iommu_spec.args[0];
 
 	return 0;
 }
 
-void xen_grant_setup_dma_ops(struct device *dev)
+static int xen_grant_init_backend_domid(struct device *dev,
+					domid_t *backend_domid)
+{
+	int ret = -ENODEV;
+
+	if (dev->of_node) {
+		ret = xen_dt_grant_init_backend_domid(dev, backend_domid);
+	} else if (IS_ENABLED(CONFIG_XEN_VIRTIO_FORCE_GRANT) || xen_pv_domain()) {
+		dev_info(dev, "Using dom0 as backend\n");
+		*backend_domid = 0;
+		ret = 0;
+	}
+
+	return ret;
+}
+
+static void xen_grant_setup_dma_ops(struct device *dev, domid_t backend_domid)
 {
 	struct xen_grant_dma_data *data;
 
···
 	if (!data)
 		goto err;
 
-	if (dev->of_node) {
-		if (xen_dt_grant_init_backend_domid(dev, data))
-			goto err;
-	} else if (IS_ENABLED(CONFIG_XEN_VIRTIO_FORCE_GRANT)) {
-		dev_info(dev, "Using dom0 as backend\n");
-		data->backend_domid = 0;
-	} else {
-		/* XXX ACPI device unsupported for now */
-		goto err;
-	}
+	data->backend_domid = backend_domid;
 
 	if (store_xen_grant_dma_data(dev, data)) {
 		dev_err(dev, "Cannot store Xen grant DMA data\n");
···
 
 bool xen_virtio_restricted_mem_acc(struct virtio_device *dev)
 {
-	bool ret = xen_virtio_mem_acc(dev);
+	domid_t backend_domid;
 
-	if (ret)
-		xen_grant_setup_dma_ops(dev->dev.parent);
+	if (!xen_grant_init_backend_domid(dev->dev.parent, &backend_domid)) {
+		xen_grant_setup_dma_ops(dev->dev.parent, backend_domid);
+		return true;
+	}
 
-	return ret;
+	return false;
 }
 
 MODULE_DESCRIPTION("Xen grant DMA-mapping layer");

include/xen/arm/xen-ops.h

···
 static inline void xen_setup_dma_ops(struct device *dev)
 {
 #ifdef CONFIG_XEN
-	if (xen_is_grant_dma_device(dev))
-		xen_grant_setup_dma_ops(dev);
-	else if (xen_swiotlb_detect())
+	if (xen_swiotlb_detect())
 		dev->dma_ops = &xen_swiotlb_dma_ops;
 #endif
 }

include/xen/xen-ops.h

···
 #endif /* CONFIG_XEN_PV && !CONFIG_PREEMPTION */
 
 #ifdef CONFIG_XEN_GRANT_DMA_OPS
-void xen_grant_setup_dma_ops(struct device *dev);
-bool xen_is_grant_dma_device(struct device *dev);
-bool xen_virtio_mem_acc(struct virtio_device *dev);
 bool xen_virtio_restricted_mem_acc(struct virtio_device *dev);
 #else
-static inline void xen_grant_setup_dma_ops(struct device *dev)
-{
-}
-static inline bool xen_is_grant_dma_device(struct device *dev)
-{
-	return false;
-}
-
 struct virtio_device;
-
-static inline bool xen_virtio_mem_acc(struct virtio_device *dev)
-{
-	return false;
-}
 
 static inline bool xen_virtio_restricted_mem_acc(struct virtio_device *dev)
 {