[PATCH v4 04/15] PCI: Add pci_find_vsec_capability() to find a specific VSEC

[Gustavo Pimentel]

Add pci_find_vsec_capability() that crawls through the device config
space searching in all Vendor-Specific Extended Capabilities for a
particular capability ID.

Vendor-Specific Extended Capability (VSEC) is a PCIe capability (acts
like a wrapper) specified by PCI-SIG that allows the vendor to create
their own and specific capability in the device config space.

Signed-off-by: Gustavo Pimentel <gustavo.pimentel@xxxxxxxxxxxx>
---
 drivers/pci/pci.c             | 34 ++++++++++++++++++++++++++++++++++
 include/linux/pci.h           |  2 ++
 include/uapi/linux/pci_regs.h |  6 ++++++
 3 files changed, 42 insertions(+)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index b9fecc2..1307af6 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -693,6 +693,40 @@ u8 pci_find_ht_capability(struct pci_dev *dev, int ht_cap)
 EXPORT_SYMBOL_GPL(pci_find_ht_capability);
 
 /**
+ * pci_find_vsec_capability - Find a vendor-specific extended capability
+ * @dev: PCI device to query
+ * @cap: vendor-specific capability ID code
+ *
+ * Typically this function will be called by the pci driver, which passes
+ * through argument the 'struct pci_dev *' already pointing for the device
+ * config space that is associated with the vendor and device ID which will
+ * know which ID to search and what to do with it, however, it might be
+ * cases that this function could be called outside of this scope and
+ * therefore is the caller responsibility to check the vendor and/or
+ * device ID first.
+ *
+ * Returns the address of the vendor-specific structure that matches the
+ * requested capability ID code within the device's PCI configuration space
+ * or 0 if it does not find a match.
+ */
+u16 pci_find_vsec_capability(struct pci_dev *dev, int vsec_cap_id)
+{
+	u16 vsec = 0;
+	u32 header;
+
+	while ((vsec = pci_find_next_ext_capability(dev, vsec,
+						     PCI_EXT_CAP_ID_VNDR))) {
+		if (pci_read_config_dword(dev, vsec + PCI_VSEC_HDR,
+					  &header) == PCIBIOS_SUCCESSFUL &&
+		    PCI_VSEC_CAP_ID(header) == vsec_cap_id)
+			return vsec;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(pci_find_vsec_capability);
+
+/**
  * pci_find_parent_resource - return resource region of parent bus of given
  *			      region
  * @dev: PCI device structure contains resources to be searched
diff --git a/include/linux/pci.h b/include/linux/pci.h
index b32126d..da6ab6a 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -1080,6 +1080,8 @@ struct pci_bus *pci_find_next_bus(const struct pci_bus *from);
 
 u64 pci_get_dsn(struct pci_dev *dev);
 
+u16 pci_find_vsec_capability(struct pci_dev *dev, int vsec_cap_id);
+
 struct pci_dev *pci_get_device(unsigned int vendor, unsigned int device,
 			       struct pci_dev *from);
 struct pci_dev *pci_get_subsys(unsigned int vendor, unsigned int device,
diff --git a/include/uapi/linux/pci_regs.h b/include/uapi/linux/pci_regs.h
index e709ae8..deae275 100644
--- a/include/uapi/linux/pci_regs.h
+++ b/include/uapi/linux/pci_regs.h
@@ -983,6 +983,12 @@
 #define PCI_VSEC_HDR		4	/* extended cap - vendor-specific */
 #define  PCI_VSEC_HDR_LEN_SHIFT	20	/* shift for length field */
 
+/* Vendor-Specific Extended Capabilities */
+#define PCI_VSEC_HEADER		4	/* Vendor-Specific Header */
+#define  PCI_VSEC_CAP_ID(x)	((x) & 0xffff)
+#define  PCI_VSEC_CAP_REV(x)	(((x) >> 16) & 0xf)
+#define  PCI_VSEC_CAP_LEN(x)	(((x) >> 20) & 0xfff)
+
 /* SATA capability */
 #define PCI_SATA_REGS		4	/* SATA REGs specifier */
 #define  PCI_SATA_REGS_MASK	0xF	/* location - BAR#/inline */
-- 
2.7.4