PCI: rcar-gen4: Add R-Car Gen4 PCIe controller support for host mode

Add R-Car Gen4 PCIe controller support for host mode.

This controller is based on Synopsys DesignWare PCIe. However, this
particular controller has a number of vendor-specific registers, and as
such, requires initialization code like mode setting and retraining and
so on.

Link: https://lore.kernel.org/linux-pci/20231018085631.1121289-13-yoshihiro.shimoda.uh@renesas.com
Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Reviewed-by: Serge Semin <fancer.lancer@gmail.com>

Author: shimoday

drivers/pci/controller/dwc/Kconfig

@@ -286,6 +286,20 @@ config PCIE_QCOM_EP
 	  to work in endpoint mode. The PCIe controller uses the DesignWare core
 	  plus Qualcomm-specific hardware wrappers.
 
+config PCIE_RCAR_GEN4
+	tristate
+
+config PCIE_RCAR_GEN4_HOST
+	tristate "Renesas R-Car Gen4 PCIe controller (host mode)"
+	depends on ARCH_RENESAS || COMPILE_TEST
+	depends on PCI_MSI
+	select PCIE_DW_HOST
+	select PCIE_RCAR_GEN4
+	help
+	  Say Y here if you want PCIe controller (host mode) on R-Car Gen4 SoCs.
+	  To compile this driver as a module, choose M here: the module will be
+	  called pcie-rcar-gen4.ko. This uses the DesignWare core.
+
 config PCIE_ROCKCHIP_DW_HOST
 	bool "Rockchip DesignWare PCIe controller"
 	select PCIE_DW

drivers/pci/controller/dwc/Makefile

@@ -26,6 +26,7 @@ obj-$(CONFIG_PCIE_TEGRA194) += pcie-tegra194.o
 obj-$(CONFIG_PCIE_UNIPHIER) += pcie-uniphier.o
 obj-$(CONFIG_PCIE_UNIPHIER_EP) += pcie-uniphier-ep.o
 obj-$(CONFIG_PCIE_VISCONTI_HOST) += pcie-visconti.o
+obj-$(CONFIG_PCIE_RCAR_GEN4) += pcie-rcar-gen4.o
 
 # The following drivers are for devices that use the generic ACPI
 # pci_root.c driver but don't support standard ECAM config access.