linux-kernel - [PATCH v10 02/17] PCI/CXL: Add pcie_is

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Message-ID: <20250626224252.1415009-3-terry.bowman@amd.com>
Date: Thu, 26 Jun 2025 17:42:37 -0500
From: Terry Bowman <terry.bowman@....com>
To: <dave@...olabs.net>, <jonathan.cameron@...wei.com>,
	<dave.jiang@...el.com>, <alison.schofield@...el.com>,
	<dan.j.williams@...el.com>, <bhelgaas@...gle.com>, <shiju.jose@...wei.com>,
	<ming.li@...omail.com>, <Smita.KoralahalliChannabasappa@....com>,
	<rrichter@....com>, <dan.carpenter@...aro.org>,
	<PradeepVineshReddy.Kodamati@....com>, <lukas@...ner.de>,
	<Benjamin.Cheatham@....com>, <sathyanarayanan.kuppuswamy@...ux.intel.com>,
	<terry.bowman@....com>, <linux-cxl@...r.kernel.org>
CC: <linux-kernel@...r.kernel.org>, <linux-pci@...r.kernel.org>
Subject: [PATCH v10 02/17] PCI/CXL: Add pcie_is_cxl()

CXL and AER drivers need the ability to identify CXL devices.

Add set_pcie_cxl() with logic checking for CXL Flexbus DVSEC presence. The
CXL Flexbus DVSEC presence is used because it is required for all the CXL
PCIe devices.[1]

Add boolean 'struct pci_dev::is_cxl' with the purpose to cache the CXL
Flexbus presence.

Add function pcie_is_cxl() to return 'struct pci_dev::is_cxl'.

[1] CXL 3.1 Spec, 8.1.1 PCIe Designated Vendor-Specific Extended
    Capability (DVSEC) ID Assignment, Table 8-2

Signed-off-by: Terry Bowman <terry.bowman@....com>
Reviewed-by: Ira Weiny <ira.weiny@...el.com>
Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
Reviewed-by: Dave Jiang <dave.jiang@...el.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
---
 drivers/pci/probe.c           | 10 ++++++++++
 include/linux/pci.h           |  6 ++++++
 include/uapi/linux/pci_regs.h |  8 +++++++-
 3 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 4b8693ec9e4c..5d3548648d5c 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -1691,6 +1691,14 @@ static void set_pcie_thunderbolt(struct pci_dev *dev)
 		dev->is_thunderbolt = 1;
 }
 
+static void set_pcie_cxl(struct pci_dev *dev)
+{
+	u16 dvsec = pci_find_dvsec_capability(dev, PCI_VENDOR_ID_CXL,
+					      PCI_DVSEC_CXL_FLEXBUS);
+	if (dvsec)
+		dev->is_cxl = 1;
+}
+
 static void set_pcie_untrusted(struct pci_dev *dev)
 {
 	struct pci_dev *parent = pci_upstream_bridge(dev);
@@ -2021,6 +2029,8 @@ int pci_setup_device(struct pci_dev *dev)
 	/* Need to have dev->cfg_size ready */
 	set_pcie_thunderbolt(dev);
 
+	set_pcie_cxl(dev);
+
 	set_pcie_untrusted(dev);
 
 	if (pci_is_pcie(dev))
diff --git a/include/linux/pci.h b/include/linux/pci.h
index 05e68f35f392..79878243b681 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -453,6 +453,7 @@ struct pci_dev {
 	unsigned int	is_hotplug_bridge:1;
 	unsigned int	shpc_managed:1;		/* SHPC owned by shpchp */
 	unsigned int	is_thunderbolt:1;	/* Thunderbolt controller */
+	unsigned int	is_cxl:1;               /* Compute Express Link (CXL) */
 	/*
 	 * Devices marked being untrusted are the ones that can potentially
 	 * execute DMA attacks and similar. They are typically connected
@@ -744,6 +745,11 @@ static inline bool pci_is_vga(struct pci_dev *pdev)
 	return false;
 }
 
+static inline bool pcie_is_cxl(struct pci_dev *pci_dev)
+{
+	return pci_dev->is_cxl;
+}
+
 #define for_each_pci_bridge(dev, bus)				\
 	list_for_each_entry(dev, &bus->devices, bus_list)	\
 		if (!pci_is_bridge(dev)) {} else
diff --git a/include/uapi/linux/pci_regs.h b/include/uapi/linux/pci_regs.h
index a3a3e942dedf..fb9d77c69d5f 100644
--- a/include/uapi/linux/pci_regs.h
+++ b/include/uapi/linux/pci_regs.h
@@ -1225,9 +1225,15 @@
 /* Deprecated old name, replaced with PCI_DOE_DATA_OBJECT_DISC_RSP_3_TYPE */
 #define PCI_DOE_DATA_OBJECT_DISC_RSP_3_PROTOCOL		PCI_DOE_DATA_OBJECT_DISC_RSP_3_TYPE
 
-/* Compute Express Link (CXL r3.1, sec 8.1.5) */
+/* Compute Express Link (CXL r3.2, sec 8.1)
+ *
+ * Note that CXL DVSEC id 3 and 7 to be ignored when the CXL link state
+ * is "disconnected" (CXL r3.2, sec 9.12.3). Re-enumerate these
+ * registers on downstream link-up events.
+ */
 #define PCI_DVSEC_CXL_PORT				3
 #define PCI_DVSEC_CXL_PORT_CTL				0x0c
 #define PCI_DVSEC_CXL_PORT_CTL_UNMASK_SBR		0x00000001
+#define PCI_DVSEC_CXL_FLEXBUS				7
 
 #endif /* LINUX_PCI_REGS_H */
-- 
2.34.1