linux-kernel - [PATCH 2/2 v2] PCI/P2PDMA: Modify p2p_dma

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Message-Id: <1726733624-2142-3-git-send-email-shivasharan.srikanteshwara@broadcom.com>
Date: Thu, 19 Sep 2024 01:13:44 -0700
From: Shivasharan S <shivasharan.srikanteshwara@...adcom.com>
To: linux-pci@...r.kernel.org,
	bhelgaas@...gle.com,
	manivannan.sadhasivam@...aro.org,
	logang@...tatee.com
Cc: linux-kernel@...r.kernel.org,
	sumanesh.samanta@...adcom.com,
	sathya.prakash@...adcom.com,
	sjeaugey@...dia.com,
	Shivasharan S <shivasharan.srikanteshwara@...adcom.com>
Subject: [PATCH 2/2 v2] PCI/P2PDMA: Modify p2p_dma_distance to detect P2P links

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.

Signed-off-by: Shivasharan S <shivasharan.srikanteshwara@...adcom.com>
---
 drivers/pci/p2pdma.c       | 17 ++++++++++++++++-
 drivers/pci/pcie/portdrv.c | 34 ++++++++++++++++++++++++++++++++++
 drivers/pci/pcie/portdrv.h |  2 ++
 3 files changed, 52 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
index 4f47a13cb500..eed3b69e7293 100644
--- a/drivers/pci/p2pdma.c
+++ b/drivers/pci/p2pdma.c
@@ -21,6 +21,8 @@
 #include <linux/seq_buf.h>
 #include <linux/xarray.h>
 
+extern bool pcie_port_is_p2p_link_available(struct pci_dev *a, struct pci_dev *b);
+
 struct pci_p2pdma {
 	struct gen_pool *pool;
 	bool p2pmem_published;
@@ -576,7 +578,7 @@ 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 +608,16 @@ calc_map_type_and_dist(struct pci_dev *provider, struct pci_dev *client,
 			if (a == bb)
 				goto check_b_path_acs;
 
+			/*
+			 * 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;
+			}
+
 			bb = pci_upstream_bridge(bb);
 			dist_b++;
 		}
@@ -629,6 +641,9 @@ 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/portdrv.c b/drivers/pci/pcie/portdrv.c
index c940b4b242fd..2fe1598fc684 100644
--- a/drivers/pci/pcie/portdrv.c
+++ b/drivers/pci/pcie/portdrv.c
@@ -104,6 +104,40 @@ static bool pcie_port_is_p2p_supported(struct pci_dev *dev)
 	return false;
 }
 
+/**
+ * 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)
+{
+	u64 dsn_a, dsn_b;
+
+	/*
+	 * Check if the devices support Inter switch P2P.
+	 */
+	if (!pcie_port_is_p2p_supported(a) ||
+	    !pcie_port_is_p2p_supported(b))
+		return false;
+
+	dsn_a = pci_get_dsn(a);
+	if (!dsn_a)
+		return false;
+
+	dsn_b = pci_get_dsn(b);
+	if (!dsn_b)
+		return false;
+
+	if (dsn_a == dsn_b)
+		return true;
+
+	return false;
+}
+EXPORT_SYMBOL_GPL(pcie_port_is_p2p_link_available);
+
 /*
  * Traverse list of all PCI bridges and find devices that support Inter switch P2P
  * and have the same serial number to create report the BDF over sysfs.
diff --git a/drivers/pci/pcie/portdrv.h b/drivers/pci/pcie/portdrv.h
index 1be06cb45665..b341aad6eb49 100644
--- a/drivers/pci/pcie/portdrv.h
+++ b/drivers/pci/pcie/portdrv.h
@@ -130,5 +130,7 @@ static inline bool pcie_pme_no_msi(void) { return false; }
 static inline void pcie_pme_interrupt_enable(struct pci_dev *dev, bool en) {}
 #endif /* !CONFIG_PCIE_PME */
 
+bool pcie_port_is_p2p_link_available(struct pci_dev *a, struct pci_dev *b);
+
 struct device *pcie_port_find_device(struct pci_dev *dev, u32 service);
 #endif /* _PORTDRV_H_ */
-- 
2.43.0