[PATCH V4 1/2] xen/virtio: Optimize the setup of "xen-grant-dma" devices

[Oleksandr Tyshchenko <olekstysh@xxxxxxxxx>]

From: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>

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 <oleksandr_tyshchenko@xxxxxxxx>
---
New patch
---
 arch/arm/xen/enlighten.c    |  2 +-
 drivers/xen/grant-dma-ops.c | 77 ++++++++++++++-----------------------
 include/xen/arm/xen-ops.h   |  4 +-
 include/xen/xen-ops.h       | 16 --------
 4 files changed, 30 insertions(+), 69 deletions(-)

diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
index 93c8ccbf2982..7d59765aef22 100644
--- a/arch/arm/xen/enlighten.c
+++ b/arch/arm/xen/enlighten.c
@@ -445,7 +445,7 @@ static int __init xen_guest_init(void)
                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();
diff --git a/drivers/xen/grant-dma-ops.c b/drivers/xen/grant-dma-ops.c
index daa525df7bdc..1e797a043980 100644
--- a/drivers/xen/grant-dma-ops.c
+++ b/drivers/xen/grant-dma-ops.c
@@ -292,50 +292,20 @@ static const struct dma_map_ops xen_grant_dma_ops = {
        .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;
        }
@@ -346,12 +316,28 @@ static int xen_dt_grant_init_backend_domid(struct device 
*dev,
         * 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;
 
@@ -365,16 +351,7 @@ void xen_grant_setup_dma_ops(struct device *dev)
        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");
@@ -392,12 +369,14 @@ void xen_grant_setup_dma_ops(struct device *dev)
 
 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");
diff --git a/include/xen/arm/xen-ops.h b/include/xen/arm/xen-ops.h
index b0766a660338..70073f5a2b54 100644
--- a/include/xen/arm/xen-ops.h
+++ b/include/xen/arm/xen-ops.h
@@ -8,9 +8,7 @@
 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
 }
diff --git a/include/xen/xen-ops.h b/include/xen/xen-ops.h
index a34f4271a2e9..47f11bec5e90 100644
--- a/include/xen/xen-ops.h
+++ b/include/xen/xen-ops.h
@@ -216,26 +216,10 @@ static inline void xen_preemptible_hcall_end(void) { }
 #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)
 {
        return false;
-- 
2.25.1