[PATCH V2 6/7] xen/grant-dma-ops: Retrieve the ID of backend's domain for DT devices

[Oleksandr Tyshchenko <olekstysh@gmail.com>]

From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>

Use the presence of recently introduced "xen,dev-domid" property
in the device node as a clear indicator of enabling Xen grant
mappings scheme for that device and read the ID of Xen domain where
the corresponding backend resides. The ID (domid) is used as
an argument to the Xen grant mapping APIs.

Also introduce xen_is_grant_dma_device() to check whether xen-grant
DMA ops need to be set for a passed device.

Remove the hardcoded domid 0 in xen_grant_setup_dma_ops().

Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
---
Changes RFC -> V1:
   - new patch, split required changes from commit:
    "[PATCH 4/6] virtio: Various updates to xen-virtio DMA ops layer"
   - update checks in xen_virtio_setup_dma_ops() to only support
     DT devices for now
   - remove the "virtio,mmio" check from xen_is_virtio_device()
   - remane everything according to the new naming scheme:
     s/virtio/grant_dma

Changes V1 -> V2:
   - remove dev_is_pci() check in xen_grant_setup_dma_ops()
   - remove EXPORT_SYMBOL_GPL(xen_is_grant_dma_device);
---
 drivers/xen/grant-dma-ops.c | 24 +++++++++++++++++-------
 include/xen/xen-ops.h       |  5 +++++
 2 files changed, 22 insertions(+), 7 deletions(-)

diff --git a/drivers/xen/grant-dma-ops.c b/drivers/xen/grant-dma-ops.c
index 29ad7bf..8924178 100644
--- a/drivers/xen/grant-dma-ops.c
+++ b/drivers/xen/grant-dma-ops.c
@@ -55,11 +55,6 @@ static struct xen_grant_dma_data *find_xen_grant_dma_data(struct device *dev)
  * Such a DMA address is formed by using the grant reference as a frame
  * number and setting the highest address bit (this bit is for the backend
  * to be able to distinguish it from e.g. a mmio address).
- *
- * Note that for now we hard wire dom0 to be the backend domain. In order
- * to support any domain as backend we'd need to add a way to communicate
- * the domid of this backend, e.g. via Xenstore, via the PCI-device's
- * config space or DT/ACPI.
  */
 static void *xen_grant_dma_alloc(struct device *dev, size_t size,
 				 dma_addr_t *dma_handle, gfp_t gfp,
@@ -275,6 +270,15 @@ static const struct dma_map_ops xen_grant_dma_ops = {
 	.dma_supported = xen_grant_dma_supported,
 };
 
+bool xen_is_grant_dma_device(struct device *dev)
+{
+	/* XXX Handle only DT devices for now */
+	if (!dev->of_node)
+		return false;
+
+	return of_property_read_bool(dev->of_node, "xen,dev-domid");
+}
+
 void xen_grant_setup_dma_ops(struct device *dev)
 {
 	struct xen_grant_dma_data *data;
@@ -286,8 +290,14 @@ void xen_grant_setup_dma_ops(struct device *dev)
 		return;
 	}
 
-	/* XXX The dom0 is hardcoded as the backend domain for now */
-	dev_domid = 0;
+	/* XXX ACPI device unsupported for now */
+	if (!dev->of_node)
+		goto err;
+
+	if (of_property_read_u32(dev->of_node, "xen,dev-domid", &dev_domid)) {
+		dev_err(dev, "xen,dev-domid property is not present\n");
+		goto err;
+	}
 
 	data = devm_kzalloc(dev, sizeof(*data), GFP_KERNEL);
 	if (!data)
diff --git a/include/xen/xen-ops.h b/include/xen/xen-ops.h
index 4f9fad5..62be9dc 100644
--- a/include/xen/xen-ops.h
+++ b/include/xen/xen-ops.h
@@ -223,10 +223,15 @@ static inline void xen_preemptible_hcall_end(void) { }
 
 #ifdef CONFIG_XEN_GRANT_DMA_OPS
 void xen_grant_setup_dma_ops(struct device *dev);
+bool xen_is_grant_dma_device(struct 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;
+}
 #endif /* CONFIG_XEN_GRANT_DMA_OPS */
 
 #endif /* INCLUDE_XEN_OPS_H */
-- 
2.7.4