netdev - [RFC 1/2] Set steering-tag directly for PCIe P2P memory access

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Message-ID: <20251113213712.776234-2-zhipingz@meta.com>
Date: Thu, 13 Nov 2025 13:37:11 -0800
From: Zhiping Zhang <zhipingz@...a.com>
To: Jason Gunthorpe <jgg@...pe.ca>, Leon Romanovsky <leon@...nel.org>,
        Bjorn
 Helgaas <bhelgaas@...gle.com>, <linux-rdma@...r.kernel.org>,
        <linux-pci@...r.kernel.org>, <netdev@...r.kernel.org>,
        Keith Busch
	<kbusch@...nel.org>, Yochai Cohen <yochai@...dia.com>,
        Yishai Hadas
	<yishaih@...dia.com>
CC: Zhiping Zhang <zhipingz@...a.com>
Subject: [RFC 1/2] Set steering-tag directly for PCIe P2P memory access

PCIe: Add a memory type for P2P memory access

The current tph memory type definition applies for CPU use cases. For device
memory accessed in the peer-to-peer (P2P) manner, we need another memory
type.

Signed-off-by: Zhiping Zhang <zhipingz@...a.com>
---
 drivers/pci/tph.c       | 4 ++++
 include/linux/pci-tph.h | 4 +++-
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/tph.c b/drivers/pci/tph.c
index cc64f93709a4..d983c9778c72 100644
--- a/drivers/pci/tph.c
+++ b/drivers/pci/tph.c
@@ -67,6 +67,8 @@ static u16 tph_extract_tag(enum tph_mem_type mem_type, u8 req_type,
 			if (info->pm_st_valid)
 				return info->pm_st;
 			break;
+		default:
+			return 0;
 		}
 		break;
 	case PCI_TPH_REQ_EXT_TPH: /* 16-bit tag */
@@ -79,6 +81,8 @@ static u16 tph_extract_tag(enum tph_mem_type mem_type, u8 req_type,
 			if (info->pm_xst_valid)
 				return info->pm_xst;
 			break;
+		default:
+			return 0;
 		}
 		break;
 	default:
diff --git a/include/linux/pci-tph.h b/include/linux/pci-tph.h
index 9e4e331b1603..b989302b6755 100644
--- a/include/linux/pci-tph.h
+++ b/include/linux/pci-tph.h
@@ -14,10 +14,12 @@
  * depending on the memory type: Volatile Memory or Persistent Memory. When a
  * caller query about a target's Steering Tag, it must provide the target's
  * tph_mem_type. ECN link: https://members.pcisig.com/wg/PCI-SIG/document/15470.
+ * Add a new tph type for PCI peer-to-peer access use case.
  */
 enum tph_mem_type {
 	TPH_MEM_TYPE_VM,	/* volatile memory */
-	TPH_MEM_TYPE_PM		/* persistent memory */
+	TPH_MEM_TYPE_PM,	/* persistent memory */
+	TPH_MEM_TYPE_P2P	/* peer-to-peer accessable memory */
 };
 
 #ifdef CONFIG_PCIE_TPH
-- 
2.47.3