[PATCH v3 15/16] PCI: dwc: tegra194: Use cached PCIe capability offset

[Hans Zhang <18255117159@163.com>]

In host mode: tegra_pcie_dw_host_init() runs inside .start_link, which is
called after dw_pcie_host_init() has cached the offset. However, the
driver's own initialization already enables hardware, so calling
dw_pcie_get_pcie_cap() is safe and will return the cached value.

In endpoint mode: pex_ep_event_pex_rst_deassert() runs after hardware is
enabled (PERST# deassert). Because the core no longer caches automatically,
we call dw_pcie_get_pcie_cap() here to cache the offset for subsequent
accesses. The helper performs the DBI read only when hardware is ready.

Thus, the private pcie_cap_base is always valid and can still be used for
register accesses.

Signed-off-by: Hans Zhang <18255117159@163.com>
---
In pcie-tegra194, dw_pcie_find_capability() appears in:

  static const struct dw_pcie_ops tegra_dw_pcie_ops = {
    .start_link = tegra_pcie_dw_start_link,
  };
  tegra_pcie_dw_start_link()
    -> tegra_pcie_dw_host_init()
      -> dw_pcie_find_capability()

  tegra_pcie_dw_probe()
    case DW_PCIE_EP_TYPE:
      tegra_pcie_config_ep()
        -> pex_ep_event_pex_rst_deassert()
	  -> dw_pcie_find_capability()
---
 drivers/pci/controller/dwc/pcie-tegra194.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/drivers/pci/controller/dwc/pcie-tegra194.c b/drivers/pci/controller/dwc/pcie-tegra194.c
index 795cef5a915d..bf482bc66a92 100644
--- a/drivers/pci/controller/dwc/pcie-tegra194.c
+++ b/drivers/pci/controller/dwc/pcie-tegra194.c
@@ -905,8 +905,7 @@ static int tegra_pcie_dw_host_init(struct dw_pcie_rp *pp)
 	pp->bridge->ops = &tegra_pci_ops;
 
 	if (!pcie->pcie_cap_base)
-		pcie->pcie_cap_base = dw_pcie_find_capability(&pcie->pci,
-							      PCI_CAP_ID_EXP);
+		pcie->pcie_cap_base = dw_pcie_get_pcie_cap(pci);
 
 	val = dw_pcie_readl_dbi(pci, PCI_IO_BASE);
 	val &= ~(IO_BASE_IO_DECODE | IO_BASE_IO_DECODE_BIT8);
@@ -1889,8 +1888,7 @@ static void pex_ep_event_pex_rst_deassert(struct tegra_pcie_dw *pcie)
 		dw_pcie_writel_dbi(pci, GEN3_RELATED_OFF, val);
 	}
 
-	pcie->pcie_cap_base = dw_pcie_find_capability(&pcie->pci,
-						      PCI_CAP_ID_EXP);
+	pcie->pcie_cap_base = dw_pcie_get_pcie_cap(pci);
 
 	/* Clear Slot Clock Configuration bit if SRNS configuration */
 	if (pcie->enable_srns) {
-- 
2.34.1