[RFC PATCH 2/2] pcie: sideband data by dropping RID bits

[Srinath Mannam <srinath.mannam@broadcom.com>]

The MSI Device ID or Stream ID are passed as sideband
data on the SOC bus to which PCI RC is connected.

If sideband data on SOC bus is less than 16bits then
PCI RC will have to derive sideband data from RID by
dropping selected bits.

This patch implements optional DT properties to generate
smaller sideband data from RID which can be further
mapped to MSI Device ID or Stream ID.

Sideband data generation from RID is done by dropping
bits corresponding zero bits in {iommu/msi}-map-drop-mask.

Example: If drop-mask is 0xFF09 then sideband data is
8 bits bus number followed by 1 bit of device number and
1 bit function number. This means drop-mask=0xFF09 will
convert RID=0x1a10 (16bits) to sideband data 0x6a (10bits).

Signed-off-by: Anup Patel <anup.patel@broadcom.com>
Signed-off-by: Oza Pawandeep <oza.oza@broadcom.com>
Signed-off-by: Srinath Mannam <srinath.mannam@broadcom.com>
Reviewed-by: Ray Jui <ray.jui@broadcom.com>
Reviewed-by: Scott Branden <scott.branden@broadcom.com>
---
 drivers/iommu/of_iommu.c |  4 ++--
 drivers/of/irq.c         |  3 ++-
 drivers/of/of_pci.c      | 48 +++++++++++++++++++++++++++++++++++++++++++++---
 include/linux/of_pci.h   |  6 ++++--
 4 files changed, 53 insertions(+), 8 deletions(-)

diff --git a/drivers/iommu/of_iommu.c b/drivers/iommu/of_iommu.c
index 19779b8..f179724 100644
--- a/drivers/iommu/of_iommu.c
+++ b/drivers/iommu/of_iommu.c
@@ -169,8 +169,8 @@ static const struct iommu_ops
 	 */
 	iommu_spec.np = NULL;
 	err = of_pci_map_rid(bridge_np, iommu_spec.args[0], "iommu-map",
-			     "iommu-map-mask", &iommu_spec.np,
-			     iommu_spec.args);
+			     "iommu-map-mask", "iommu-map-drop-mask",
+			     &iommu_spec.np, iommu_spec.args);
 	if (err)
 		return err == -ENODEV ? NULL : ERR_PTR(err);
 
diff --git a/drivers/of/irq.c b/drivers/of/irq.c
index d11437c..454f47a 100644
--- a/drivers/of/irq.c
+++ b/drivers/of/irq.c
@@ -606,7 +606,8 @@ static u32 __of_msi_map_rid(struct device *dev, struct device_node **np,
 	 */
 	for (parent_dev = dev; parent_dev; parent_dev = parent_dev->parent)
 		if (!of_pci_map_rid(parent_dev->of_node, rid_in, "msi-map",
-				    "msi-map-mask", np, &rid_out))
+				    "msi-map-mask", "msi-map-drop-mask", np,
+				    &rid_out))
 			break;
 	return rid_out;
 }
diff --git a/drivers/of/of_pci.c b/drivers/of/of_pci.c
index c9d4d3a..a914bcf 100644
--- a/drivers/of/of_pci.c
+++ b/drivers/of/of_pci.c
@@ -285,6 +285,35 @@ int of_pci_get_host_bridge_resources(struct device_node *dev,
 EXPORT_SYMBOL_GPL(of_pci_get_host_bridge_resources);
 #endif /* CONFIG_OF_ADDRESS */
 
+static inline u32 out_masked_rid(u32 rid, u32 drop_mask)
+{
+	u32 id = 0;
+	u32 i = 0;
+
+	/* RID's BUS, DEV, FUN values not inside the mask are invalid */
+	if (rid & ~drop_mask)
+		return -EINVAL;
+
+	/*
+	 * RID value is translated to sideband data using drop_mask
+	 * by dropping bits corresponding zero bits in drop_mask.
+	 *
+	 * Example: If drop_mask is 0xFF09 then sideband data is
+	 * 8 bits bus number followed by 1 bit of device number and
+	 * 1 bit function number. This means drop_mask=0xFF09 will
+	 * convert RID=0x1a10 (16bits) to sideband data 0x6a (10bits).
+	 */
+	while (drop_mask) {
+		if (drop_mask & 0x1) {
+			id |= ((rid & 0x1) << i);
+			i++;
+		}
+		rid = rid >> 1;
+		drop_mask = drop_mask >> 1;
+	}
+
+	return id;
+}
 /**
  * of_pci_map_rid - Translate a requester ID through a downstream mapping.
  * @np: root complex device node.
@@ -304,11 +333,11 @@ EXPORT_SYMBOL_GPL(of_pci_get_host_bridge_resources);
  *
  * Return: 0 on success or a standard error code on failure.
  */
-int of_pci_map_rid(struct device_node *np, u32 rid,
-		   const char *map_name, const char *map_mask_name,
+int of_pci_map_rid(struct device_node *np, u32 rid, const char *map_name,
+		   const char *map_mask_name, const char *drop_mask_name,
 		   struct device_node **target, u32 *id_out)
 {
-	u32 map_mask, masked_rid;
+	u32 map_mask, masked_rid, drop_mask;
 	int map_len;
 	const __be32 *map = NULL;
 
@@ -340,7 +369,20 @@ int of_pci_map_rid(struct device_node *np, u32 rid,
 	if (map_mask_name)
 		of_property_read_u32(np, map_mask_name, &map_mask);
 
+	/* The default is to select all bits. */
+	drop_mask = 0xffffffff;
+
+	/*
+	 * Can be overridden by "{iommu,msi}-map-drop-mask" property.
+	 * If of_property_read_u32() fails, the default is used.
+	 */
+	if (drop_mask_name)
+		of_property_read_u32(np, drop_mask_name, &drop_mask);
+
 	masked_rid = map_mask & rid;
+
+	masked_rid = out_masked_rid(masked_rid, drop_mask);
+
 	for ( ; map_len > 0; map_len -= 4 * sizeof(*map), map += 4) {
 		struct device_node *phandle_node;
 		u32 rid_base = be32_to_cpup(map + 0);
diff --git a/include/linux/of_pci.h b/include/linux/of_pci.h
index 518c8d2..98937ec 100644
--- a/include/linux/of_pci.h
+++ b/include/linux/of_pci.h
@@ -20,7 +20,8 @@ int of_pci_get_max_link_speed(struct device_node *node);
 void of_pci_check_probe_only(void);
 int of_pci_map_rid(struct device_node *np, u32 rid,
 		   const char *map_name, const char *map_mask_name,
-		   struct device_node **target, u32 *id_out);
+		   const char *drop_mask_name, struct device_node **target,
+		   u32 *id_out);
 #else
 static inline int of_irq_parse_pci(const struct pci_dev *pdev, struct of_phandle_args *out_irq)
 {
@@ -58,7 +59,8 @@ of_get_pci_domain_nr(struct device_node *node)
 
 static inline int of_pci_map_rid(struct device_node *np, u32 rid,
 			const char *map_name, const char *map_mask_name,
-			struct device_node **target, u32 *id_out)
+			const char *drop_mask_name, struct device_node **target,
+			u32 *id_out)
 {
 	return -EINVAL;
 }
-- 
2.7.4