[PATCH v3 2/2] PCI/P2PDMA: Modify p2p_dma_distance to detect P2P links

[Shivasharan S <shivasharan.srikanteshwara@xxxxxxxxxxxx>]

Update the p2p_dma_distance() to determine inter-switch P2P links existing
between two switches and use this to calculate the DMA distance between
two devices. This requires enabling the PCIE_P2P_LINK config option in
the kernel.

Signed-off-by: Shivasharan S <shivasharan.srikanteshwara@xxxxxxxxxxxx>
---
Changes in v3:
Fixed review comments from Jonathan

 drivers/pci/p2pdma.c        | 18 +++++++++++++++++-
 drivers/pci/pcie/p2p_link.c | 18 ++++++++++++++++++
 drivers/pci/pcie/p2p_link.h |  5 +++++
 3 files changed, 40 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
index 7abd4f546d3c..9482bf0b1a02 100644
--- a/drivers/pci/p2pdma.c
+++ b/drivers/pci/p2pdma.c
@@ -20,6 +20,7 @@
 #include <linux/random.h>
 #include <linux/seq_buf.h>
 #include <linux/xarray.h>
+#include "pcie/p2p_link.h"
 
 struct pci_p2pdma {
 	struct gen_pool *pool;
@@ -576,7 +577,7 @@ calc_map_type_and_dist(struct pci_dev *provider, struct pci_dev *client,
 		int *dist, bool verbose)
 {
 	enum pci_p2pdma_map_type map_type = PCI_P2PDMA_MAP_THRU_HOST_BRIDGE;
-	struct pci_dev *a = provider, *b = client, *bb;
+	struct pci_dev *a = provider, *b = client, *bb, *b_p2p_link = NULL;
 	bool acs_redirects = false;
 	struct pci_p2pdma *p2pdma;
 	struct seq_buf acs_list;
@@ -606,6 +607,18 @@ calc_map_type_and_dist(struct pci_dev *provider, struct pci_dev *client,
 			if (a == bb)
 				goto check_b_path_acs;
 
+#ifdef CONFIG_PCIE_P2P_LINK
+			/*
+			 * If both upstream bridges have Inter switch P2P link
+			 * available, P2P DMA distance can account for optimized
+			 * path.
+			 */
+			if (pcie_port_is_p2p_link_available(a, bb)) {
+				b_p2p_link = bb;
+				goto check_b_path_acs;
+			}
+#endif
+
 			bb = pci_upstream_bridge(bb);
 			dist_b++;
 		}
@@ -629,6 +642,9 @@ calc_map_type_and_dist(struct pci_dev *provider, struct pci_dev *client,
 			acs_cnt++;
 		}
 
+		if (bb == b_p2p_link)
+			break;
+
 		bb = pci_upstream_bridge(bb);
 	}
 
diff --git a/drivers/pci/pcie/p2p_link.c b/drivers/pci/pcie/p2p_link.c
index dec5c4cbcf13..87651dfa1981 100644
--- a/drivers/pci/pcie/p2p_link.c
+++ b/drivers/pci/pcie/p2p_link.c
@@ -141,3 +141,21 @@ void p2p_link_sysfs_update_group(struct pci_dev *pdev)
 
 	sysfs_update_group(&pdev->dev.kobj, &pcie_port_p2p_link_attr_group);
 }
+
+/*
+ * pcie_port_is_p2p_link_available: Determine if a P2P link is available
+ * between the two upstream bridges. The serial number of the two devices
+ * will be compared and if they are same then it is considered that the P2P
+ * link is available.
+ *
+ * Return value: true if inter switch P2P is available, return false otherwise.
+ */
+bool pcie_port_is_p2p_link_available(struct pci_dev *a, struct pci_dev *b)
+{
+	if (!pcie_port_is_p2p_supported(a) || !pcie_port_is_p2p_supported(b))
+		return false;
+
+	/* the above check validates DSN is valid for both devices */
+	return pci_get_dsn(a) == pci_get_dsn(b);
+}
+EXPORT_SYMBOL_GPL(pcie_port_is_p2p_link_available);
diff --git a/drivers/pci/pcie/p2p_link.h b/drivers/pci/pcie/p2p_link.h
index 6c4f57841c79..6677ed66f397 100644
--- a/drivers/pci/pcie/p2p_link.h
+++ b/drivers/pci/pcie/p2p_link.h
@@ -21,7 +21,12 @@
 #ifdef CONFIG_PCIE_P2P_LINK
 void p2p_link_sysfs_update_group(struct pci_dev *pdev);
 
+bool pcie_port_is_p2p_link_available(struct pci_dev *a, struct pci_dev *b);
 #else
 static inline void p2p_link_sysfs_update_group(struct pci_dev *pdev) { }
+static inline bool pcie_port_is_p2p_link_available(struct pci_dev *a, struct pci_dev *b)
+{
+	return false;
+}
 #endif
 #endif /* _P2P_LINK_H_ */
-- 
2.43.0