PCI: dwc: Add extended configuration space capability search API

Add extended configuration space capability search API using struct
dw_pcie* pointer.
Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Acked-by: Gustavo Pimentel <gustavo.pimentel@synopsys.com>
Acked-by: Thierry Reding <treding@nvidia.com>

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

@@ -53,6 +53,47 @@ u8 dw_pcie_find_capability(struct dw_pcie *pci, u8 cap)
 }
 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);
+}
+EXPORT_SYMBOL_GPL(dw_pcie_find_ext_capability);
+
 int dw_pcie_read(void __iomem *addr, int size, u32 *val)
 {
 	if (!IS_ALIGNED((uintptr_t)addr, size)) {

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

@@ -252,6 +252,7 @@ struct dw_pcie {
 		container_of((endpoint), struct dw_pcie, ep)
 
 u8 dw_pcie_find_capability(struct dw_pcie *pci, u8 cap);
+u16 dw_pcie_find_ext_capability(struct dw_pcie *pci, u8 cap);
 
 int dw_pcie_read(void __iomem *addr, int size, u32 *val);
 int dw_pcie_write(void __iomem *addr, int size, u32 val);