linux-kernel - [PATCH 2/2] pci/p2pdma: Modify p2p_dma_distance to detect virtual P2P links

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Date: Wed, 12 Jun 2024 04:27:36 -0700
From: Shivasharan S <shivasharan.srikanteshwara@...adcom.com>
To: linux-pci@...r.kernel.org,
	bhelgaas@...gle.com
Cc: linux-kernel@...r.kernel.org,
	sumanesh.samanta@...adcom.com,
	sathya.prakash@...adcom.com,
	Shivasharan S <shivasharan.srikanteshwara@...adcom.com>
Subject: [PATCH 2/2] pci/p2pdma: Modify p2p_dma_distance to detect virtual P2P links

Update the p2p_dma_distance() to determine virtual 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/Kconfig  |  1 +
 drivers/pci/p2pdma.c | 18 +++++++++++++++++-
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/Kconfig b/drivers/pci/Kconfig
index d35001589d88..3e6226ec91fd 100644
--- a/drivers/pci/Kconfig
+++ b/drivers/pci/Kconfig
@@ -174,6 +174,7 @@ config PCI_P2PDMA
 	depends on 64BIT
 	select GENERIC_ALLOCATOR
 	select NEED_SG_DMA_FLAGS
+	select PCI_SW_DISCOVERY
 	help
 	  Enables drivers to do PCI peer-to-peer transactions to and from
 	  BARs that are exposed in other devices that are the part of
diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
index 4f47a13cb500..780e649b3a1d 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 sw_disc_check_virtual_link(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_virtual_link = NULL;
 	bool acs_redirects = false;
 	struct pci_p2pdma *p2pdma;
 	struct seq_buf acs_list;
@@ -606,6 +608,17 @@ calc_map_type_and_dist(struct pci_dev *provider, struct pci_dev *client,
 			if (a == bb)
 				goto check_b_path_acs;
 
+			// Physical Broadcom PEX switches can be provisioned into
+			// multiple virtual switches.
+			// if both upstream bridges belong to the same physical
+			// switch, and the switch supports P2P,
+			// p2p_dma_distance() should take into account of such
+			// scenarios.
+			if (sw_disc_check_virtual_link(a, bb)) {
+				b_virtual_link = bb;
+				goto check_b_path_acs;
+			}
+
 			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 (b_virtual_link && bb == b_virtual_link)
+			break;
+
 		bb = pci_upstream_bridge(bb);
 	}
 
-- 
2.43.0


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