[PATCH v3 01/16] PCI: dwc: Add pcie_cap field and helper in designware header

[Hans Zhang <18255117159@163.com>]

Add a pcie_cap field to struct dw_pcie to store the offset of the
PCI Express Capability structure. Provide a helper dw_pcie_get_pcie_cap()
which performs the capability search on first call and caches the result.

This is a preparatory step for replacing repetitive capability searches
in both core and platform drivers.

Signed-off-by: Hans Zhang <18255117159@163.com>
---
 drivers/pci/controller/dwc/pcie-designware.h | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/drivers/pci/controller/dwc/pcie-designware.h b/drivers/pci/controller/dwc/pcie-designware.h
index de4b245b1758..8113efd33a24 100644
--- a/drivers/pci/controller/dwc/pcie-designware.h
+++ b/drivers/pci/controller/dwc/pcie-designware.h
@@ -591,6 +591,8 @@ struct dw_pcie {
 	 * use_parent_dt_ranges to true to avoid this warning.
 	 */
 	bool			use_parent_dt_ranges;
+
+	u8			pcie_cap;	/* PCIe capability offset */
 };
 
 #define to_dw_pcie_from_pp(port) container_of((port), struct dw_pcie, pp)
@@ -829,6 +831,21 @@ static inline void dw_pcie_dbi_ro_wr_dis(struct dw_pcie *pci)
 	dw_pcie_writel_dbi(pci, reg, val);
 }
 
+/**
+ * dw_pcie_get_pcie_cap() - Return cached PCIe Capability offset
+ * @pci: DWC instance
+ *
+ * Finds and caches the offset of PCI_CAP_ID_EXP on first call.
+ * Returns 0 if the capability is not present.
+ */
+static inline u8 dw_pcie_get_pcie_cap(struct dw_pcie *pci)
+{
+	if (!pci->pcie_cap)
+		pci->pcie_cap = dw_pcie_find_capability(pci, PCI_CAP_ID_EXP);
+
+	return pci->pcie_cap;
+}
+
 static inline int dw_pcie_start_link(struct dw_pcie *pci)
 {
 	if (pci->ops && pci->ops->start_link)
-- 
2.34.1