PCI: Remove redundant PCI_VSEC_HDR and PCI_VSEC_HDR_LEN_SHIFT

Remove duplicate macro PCI_VSEC_HDR and its related macro
PCI_VSEC_HDR_LEN_SHIFT from pci_regs.h to avoid redundancy and
inconsistencies. Update VFIO PCI code to use PCI_VNDR_HEADER and
PCI_VNDR_HEADER_LEN() for consistent naming and functionality.

These changes aim to streamline header handling while minimizing impact,
given the niche usage of these macros in userspace.

Link: https://lore.kernel.org/r/20241216013536.4487-1-zhangdongdong@eswincomputing.com
Signed-off-by: Dongdong Zhang <zhangdongdong@eswincomputing.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Alex Williamson <alex.williamson@redhat.com>

Author: Dunky-Z

drivers/vfio/pci/vfio_pci_config.c

@@ -1389,11 +1389,12 @@ static int vfio_ext_cap_len(struct vfio_pci_core_device *vdev, u16 ecap, u16 epo
 
 	switch (ecap) {
 	case PCI_EXT_CAP_ID_VNDR:
-		ret = pci_read_config_dword(pdev, epos + PCI_VSEC_HDR, &dword);
+		ret = pci_read_config_dword(pdev, epos + PCI_VNDR_HEADER,
+					    &dword);
 		if (ret)
 			return pcibios_err_to_errno(ret);
 
-		return dword >> PCI_VSEC_HDR_LEN_SHIFT;
+		return PCI_VNDR_HEADER_LEN(dword);
 	case PCI_EXT_CAP_ID_VC:
 	case PCI_EXT_CAP_ID_VC9:
 	case PCI_EXT_CAP_ID_MFVC:

include/uapi/linux/pci_regs.h

@@ -1001,9 +1001,6 @@
 #define PCI_ACS_CTRL		0x06	/* ACS Control Register */
 #define PCI_ACS_EGRESS_CTL_V	0x08	/* ACS Egress Control Vector */
 
-#define PCI_VSEC_HDR		4	/* extended cap - vendor-specific */
-#define  PCI_VSEC_HDR_LEN_SHIFT	20	/* shift for length field */
-
 /* SATA capability */
 #define PCI_SATA_REGS		4	/* SATA REGs specifier */
 #define  PCI_SATA_REGS_MASK	0xF	/* location - BAR#/inline */