PCI: dwc: Implement capability search using PCI core APIs

The PCI core now provides generic PCI_FIND_NEXT_CAP() and
PCI_FIND_NEXT_EXT_CAP() macros to search for PCI capabilities, using
config accessors we supply.

Use them in the DWC driver to implement dw_pcie_find_capability() and
dw_pcie_find_ext_capability() instead of duplicating the algorithm.

Signed-off-by: Hans Zhang <18255117159@163.com>
[bhelgaas: commit log]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Link: https://patch.msgid.link/20250813144529.303548-5-18255117159@163.com

Author: Hans Zhang

drivers/pci/controller/dwc/pcie-designware.c

@@ -213,83 +213,16 @@ void dw_pcie_version_detect(struct dw_pcie *pci)
 		pci->type = ver;
 }
 
-/*
- * These interfaces resemble the pci_find_*capability() interfaces, but these
- * are for configuring host controllers, which are bridges *to* PCI devices but
- * are not PCI devices themselves.
- */
-static u8 __dw_pcie_find_next_cap(struct dw_pcie *pci, u8 cap_ptr,
-				  u8 cap)
-{
-	u8 cap_id, next_cap_ptr;
-	u16 reg;
-
-	if (!cap_ptr)
-		return 0;
-
-	reg = dw_pcie_readw_dbi(pci, cap_ptr);
-	cap_id = (reg & 0x00ff);
-
-	if (cap_id > PCI_CAP_ID_MAX)
-		return 0;
-
-	if (cap_id == cap)
-		return cap_ptr;
-
-	next_cap_ptr = (reg & 0xff00) >> 8;
-	return __dw_pcie_find_next_cap(pci, next_cap_ptr, cap);
-}
-
 u8 dw_pcie_find_capability(struct dw_pcie *pci, u8 cap)
 {
-	u8 next_cap_ptr;
-	u16 reg;
-
-	reg = dw_pcie_readw_dbi(pci, PCI_CAPABILITY_LIST);
-	next_cap_ptr = (reg & 0x00ff);
-
-	return __dw_pcie_find_next_cap(pci, next_cap_ptr, cap);
+	return PCI_FIND_NEXT_CAP(dw_pcie_read_cfg, PCI_CAPABILITY_LIST, cap,
+				 pci);
 }
 EXPORT_SYMBOL_GPL(dw_pcie_find_capability);
 
-static u16 dw_pcie_find_next_ext_capability(struct dw_pcie *pci, u16 start,
-					    u8 cap)
-{
-	u32 header;
-	int ttl;
-	int pos = PCI_CFG_SPACE_SIZE;
-
-	/* minimum 8 bytes per capability */
-	ttl = (PCI_CFG_SPACE_EXP_SIZE - PCI_CFG_SPACE_SIZE) / 8;
-
-	if (start)
-		pos = start;
-
-	header = dw_pcie_readl_dbi(pci, pos);
-	/*
-	 * If we have no capabilities, this is indicated by cap ID,
-	 * cap version and next pointer all being 0.
-	 */
-	if (header == 0)
-		return 0;
-
-	while (ttl-- > 0) {
-		if (PCI_EXT_CAP_ID(header) == cap && pos != start)
-			return pos;
-
-		pos = PCI_EXT_CAP_NEXT(header);
-		if (pos < PCI_CFG_SPACE_SIZE)
-			break;
-
-		header = dw_pcie_readl_dbi(pci, pos);
-	}
-
-	return 0;
-}
-
 u16 dw_pcie_find_ext_capability(struct dw_pcie *pci, u8 cap)
 {
-	return dw_pcie_find_next_ext_capability(pci, 0, cap);
+	return PCI_FIND_NEXT_EXT_CAP(dw_pcie_read_cfg, 0, cap, pci);
 }
 EXPORT_SYMBOL_GPL(dw_pcie_find_ext_capability);
 
@@ -302,8 +235,8 @@ static u16 __dw_pcie_find_vsec_capability(struct dw_pcie *pci, u16 vendor_id,
 	if (vendor_id != dw_pcie_readw_dbi(pci, PCI_VENDOR_ID))
 		return 0;
 
-	while ((vsec = dw_pcie_find_next_ext_capability(pci, vsec,
-						       PCI_EXT_CAP_ID_VNDR))) {
+	while ((vsec = PCI_FIND_NEXT_EXT_CAP(dw_pcie_read_cfg, vsec,
+					     PCI_EXT_CAP_ID_VNDR, pci))) {
 		header = dw_pcie_readl_dbi(pci, vsec + PCI_VNDR_HEADER);
 		if (PCI_VNDR_HEADER_ID(header) == vsec_id)
 			return vsec;

drivers/pci/controller/dwc/pcie-designware.h

@@ -609,6 +609,27 @@ static inline void dw_pcie_writel_dbi2(struct dw_pcie *pci, u32 reg, u32 val)
 	dw_pcie_write_dbi2(pci, reg, 0x4, val);
 }
 
+static inline int dw_pcie_read_cfg_byte(struct dw_pcie *pci, int where,
+					u8 *val)
+{
+	*val = dw_pcie_readb_dbi(pci, where);
+	return PCIBIOS_SUCCESSFUL;
+}
+
+static inline int dw_pcie_read_cfg_word(struct dw_pcie *pci, int where,
+					u16 *val)
+{
+	*val = dw_pcie_readw_dbi(pci, where);
+	return PCIBIOS_SUCCESSFUL;
+}
+
+static inline int dw_pcie_read_cfg_dword(struct dw_pcie *pci, int where,
+					 u32 *val)
+{
+	*val = dw_pcie_readl_dbi(pci, where);
+	return PCIBIOS_SUCCESSFUL;
+}
+
 static inline unsigned int dw_pcie_ep_get_dbi_offset(struct dw_pcie_ep *ep,
 						     u8 func_no)
 {