[PATCH v2 3/8] iommu/arm: Introduce iommu_add_dt_pci_device API

[Stewart Hildebrand <stewart.hildebrand@xxxxxxx>]

From: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>

The main purpose of this patch is to add a way to register PCI device
(which is behind the IOMMU) using the generic PCI-IOMMU DT bindings [1]
before assigning that device to a domain.

This behaves in almost the same way as existing iommu_add_dt_device API,
the difference is in devices to handle and DT bindings to use.

The function of_map_id to translate an ID through a downstream mapping
(which is also suitable for mapping Requester ID) was borrowed from Linux
(v5.10-rc6) and updated according to the Xen code base.

XXX: I don't port pci_for_each_dma_alias from Linux which is a part
of PCI-IOMMU bindings infrastucture as I don't have a good understanding
for how it is expected to work in Xen environment.
Also it is not completely clear whether we need to distinguish between
different PCI types here (DEV_TYPE_PCI, DEV_TYPE_PCI_HOST_BRIDGE, etc).
For example, how we should behave here if the host bridge doesn't have
a stream ID (so not described in iommu-map property) just simple
fail or bypasses translation?

[1] 
https://www.kernel.org/doc/Documentation/devicetree/bindings/pci/pci-iommu.txt

Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
Signed-off-by: Stewart Hildebrand <stewart.hildebrand@xxxxxxx>
---
v1->v2:
* remove extra devfn parameter since pdev fully describes the device
* remove ops->add_device() call from iommu_add_dt_pci_device(). Instead, rely on
  the existing iommu call in iommu_add_device().
* move the ops->add_device and ops->dt_xlate checks earlier

downstream->v1:
* rebase
* add const qualifier to struct dt_device_node *np arg in dt_map_id()
* add const qualifier to struct dt_device_node *np declaration in 
iommu_add_pci_device()
* use stdint.h types instead of u8/u32/etc...
* rename functions:
  s/dt_iommu_xlate/iommu_dt_xlate/
  s/dt_map_id/iommu_dt_pci_map_id/
  s/iommu_add_pci_device/iommu_add_dt_pci_device/
* add device_is_protected check in iommu_add_dt_pci_device
* wrap prototypes in CONFIG_HAS_PCI

(cherry picked from commit 734e3bf6ee77e7947667ab8fa96c25b349c2e1da from
 the downstream branch poc/pci-passthrough from
 https://gitlab.com/xen-project/people/bmarquis/xen-arm-poc.git)
---
 xen/drivers/passthrough/device_tree.c | 140 ++++++++++++++++++++++++++
 xen/include/xen/device_tree.h         |  25 +++++
 xen/include/xen/iommu.h               |   6 +-
 3 files changed, 170 insertions(+), 1 deletion(-)

diff --git a/xen/drivers/passthrough/device_tree.c 
b/xen/drivers/passthrough/device_tree.c
index 1b50f4670944..5e462e5c2ca8 100644
--- a/xen/drivers/passthrough/device_tree.c
+++ b/xen/drivers/passthrough/device_tree.c
@@ -151,6 +151,146 @@ static int iommu_dt_xlate(struct device *dev,
     return ops->dt_xlate(dev, iommu_spec);
 }
 
+#ifdef CONFIG_HAS_PCI
+int iommu_dt_pci_map_id(const struct dt_device_node *np, uint32_t id,
+                        const char *map_name, const char *map_mask_name,
+                        struct dt_device_node **target, uint32_t *id_out)
+{
+    uint32_t map_mask, masked_id, map_len;
+    const __be32 *map = NULL;
+
+    if ( !np || !map_name || (!target && !id_out) )
+        return -EINVAL;
+
+    map = dt_get_property(np, map_name, &map_len);
+    if ( !map )
+    {
+        if ( target )
+            return -ENODEV;
+        /* Otherwise, no map implies no translation */
+        *id_out = id;
+        return 0;
+    }
+
+    if ( !map_len || map_len % (4 * sizeof(*map)) )
+    {
+        printk(XENLOG_ERR "%pOF: Error: Bad %s length: %d\n", np,
+            map_name, map_len);
+        return -EINVAL;
+    }
+
+    /* The default is to select all bits. */
+    map_mask = 0xffffffff;
+
+    /*
+     * Can be overridden by "{iommu,msi}-map-mask" property.
+     * If of_property_read_u32() fails, the default is used.
+     */
+    if ( map_mask_name )
+        dt_property_read_u32(np, map_mask_name, &map_mask);
+
+    masked_id = map_mask & id;
+    for ( ; (int)map_len > 0; map_len -= 4 * sizeof(*map), map += 4 )
+    {
+        struct dt_device_node *phandle_node;
+        uint32_t id_base = be32_to_cpup(map + 0);
+        uint32_t phandle = be32_to_cpup(map + 1);
+        uint32_t out_base = be32_to_cpup(map + 2);
+        uint32_t id_len = be32_to_cpup(map + 3);
+
+        if ( id_base & ~map_mask )
+        {
+            printk(XENLOG_ERR "%pOF: Invalid %s translation - %s-mask (0x%x) 
ignores id-base (0x%x)\n",
+                   np, map_name, map_name, map_mask, id_base);
+            return -EFAULT;
+        }
+
+        if ( masked_id < id_base || masked_id >= id_base + id_len )
+            continue;
+
+        phandle_node = dt_find_node_by_phandle(phandle);
+        if ( !phandle_node )
+            return -ENODEV;
+
+        if ( target )
+        {
+            if ( !*target )
+                *target = phandle_node;
+
+            if ( *target != phandle_node )
+                continue;
+        }
+
+        if ( id_out )
+            *id_out = masked_id - id_base + out_base;
+
+        printk(XENLOG_DEBUG "%pOF: %s, using mask %08x, id-base: %08x, 
out-base: %08x, length: %08x, id: %08x -> %08x\n",
+               np, map_name, map_mask, id_base, out_base, id_len, id,
+               masked_id - id_base + out_base);
+        return 0;
+    }
+
+    printk(XENLOG_ERR "%pOF: no %s translation for id 0x%x on %pOF\n",
+           np, map_name, id, target && *target ? *target : NULL);
+
+    /*
+     * NOTE: Linux bypasses translation without returning an error here,
+     * but should we behave in the same way on Xen? Restrict for now.
+     */
+    return -EFAULT;
+}
+
+int iommu_add_dt_pci_device(struct pci_dev *pdev)
+{
+    const struct iommu_ops *ops = iommu_get_ops();
+    struct dt_phandle_args iommu_spec = { .args_count = 1 };
+    struct device *dev = pci_to_dev(pdev);
+    const struct dt_device_node *np;
+    int rc = NO_IOMMU;
+
+    if ( !iommu_enabled )
+        return NO_IOMMU;
+
+    if ( !ops )
+        return -EINVAL;
+
+    if ( device_is_protected(dev) )
+        return 0;
+
+    if ( dev_iommu_fwspec_get(dev) )
+        return -EEXIST;
+
+    np = pci_find_host_bridge_node(pdev);
+    if ( !np )
+        return -ENODEV;
+
+    /*
+     * The driver which supports generic PCI-IOMMU DT bindings must have
+     * these callback implemented.
+     */
+    if ( !ops->add_device || !ops->dt_xlate )
+        return -EINVAL;
+
+    /*
+     * According to the Documentation/devicetree/bindings/pci/pci-iommu.txt
+     * from Linux.
+     */
+    rc = iommu_dt_pci_map_id(np, PCI_BDF(pdev->bus, pdev->devfn), "iommu-map",
+                             "iommu-map-mask", &iommu_spec.np, 
iommu_spec.args);
+    if ( rc )
+        return rc == -ENODEV ? NO_IOMMU : rc;
+
+    rc = iommu_dt_xlate(dev, &iommu_spec);
+    if ( rc < 0 )
+    {
+        iommu_fwspec_free(pci_to_dev(pdev));
+        return -EINVAL;
+    }
+
+    return rc;
+}
+#endif /* CONFIG_HAS_PCI */
+
 int iommu_add_dt_device(struct dt_device_node *np)
 {
     const struct iommu_ops *ops = iommu_get_ops();
diff --git a/xen/include/xen/device_tree.h b/xen/include/xen/device_tree.h
index c1e4751a581f..dc40fdfb9231 100644
--- a/xen/include/xen/device_tree.h
+++ b/xen/include/xen/device_tree.h
@@ -852,6 +852,31 @@ int dt_count_phandle_with_args(const struct dt_device_node 
*np,
  */
 int dt_get_pci_domain_nr(struct dt_device_node *node);
 
+#ifdef CONFIG_HAS_PCI
+/**
+ * iommu_dt_pci_map_id - Translate an ID through a downstream mapping.
+ * @np: root complex device node.
+ * @id: device ID to map.
+ * @map_name: property name of the map to use.
+ * @map_mask_name: optional property name of the mask to use.
+ * @target: optional pointer to a target device node.
+ * @id_out: optional pointer to receive the translated ID.
+ *
+ * Given a device ID, look up the appropriate implementation-defined
+ * platform ID and/or the target device which receives transactions on that
+ * ID, as per the "iommu-map" and "msi-map" bindings. Either of @target or
+ * @id_out may be NULL if only the other is required. If @target points to
+ * a non-NULL device node pointer, only entries targeting that node will be
+ * matched; if it points to a NULL value, it will receive the device node of
+ * the first matching target phandle, with a reference held.
+ *
+ * Return: 0 on success or a standard error code on failure.
+ */
+int iommu_dt_pci_map_id(const struct dt_device_node *np, uint32_t id,
+                        const char *map_name, const char *map_mask_name,
+                        struct dt_device_node **target, uint32_t *id_out);
+#endif /* CONFIG_HAS_PCI */
+
 struct dt_device_node *dt_find_node_by_phandle(dt_phandle handle);
 
 #ifdef CONFIG_DEVICE_TREE_DEBUG
diff --git a/xen/include/xen/iommu.h b/xen/include/xen/iommu.h
index 405db59971c5..7cb4d2aa5511 100644
--- a/xen/include/xen/iommu.h
+++ b/xen/include/xen/iommu.h
@@ -219,7 +219,8 @@ int iommu_dt_domain_init(struct domain *d);
 int iommu_release_dt_devices(struct domain *d);
 
 /*
- * Helper to add master device to the IOMMU using generic IOMMU DT bindings.
+ * Helpers to add master device to the IOMMU using generic (PCI-)IOMMU
+ * DT bindings.
  *
  * Return values:
  *  0 : device is protected by an IOMMU
@@ -228,6 +229,9 @@ int iommu_release_dt_devices(struct domain *d);
  *      (IOMMU is not enabled/present or device is not connected to it).
  */
 int iommu_add_dt_device(struct dt_device_node *np);
+#ifdef CONFIG_HAS_PCI
+int iommu_add_dt_pci_device(struct pci_dev *pdev);
+#endif
 
 int iommu_do_dt_domctl(struct xen_domctl *, struct domain *,
                        XEN_GUEST_HANDLE_PARAM(xen_domctl_t));
-- 
2.40.1