PCI: xilinx-nwl: Enable coherent PCIe DMA traffic using CCI

Add support for routing PCIe DMA traffic coherently when
Cache Coherent Interconnect (CCI) is enabled in the system.
The "dma-coherent" property is used to determine if CCI is enabled
or not.
Refer to https://developer.arm.com/documentation/ddi0470/k/preface
for the CCI specification.

Link: https://lore.kernel.org/r/20210222084732.21521-1-bharat.kumar.gogada@xilinx.com
Signed-off-by: Bharat Kumar Gogada <bharat.kumar.gogada@xilinx.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>

drivers/pci/controller/pcie-xilinx-nwl.c

@@ -26,6 +26,7 @@
 
 /* Bridge core config registers */
 #define BRCFG_PCIE_RX0			0x00000000
+#define BRCFG_PCIE_RX1			0x00000004
 #define BRCFG_INTERRUPT			0x00000010
 #define BRCFG_PCIE_RX_MSG_FILTER	0x00000020
 
@@ -128,6 +129,7 @@
 #define NWL_ECAM_VALUE_DEFAULT		12
 
 #define CFG_DMA_REG_BAR			GENMASK(2, 0)
+#define CFG_PCIE_CACHE			GENMASK(7, 0)
 
 #define INT_PCI_MSI_NR			(2 * 32)
 
@@ -675,6 +677,11 @@ static int nwl_pcie_bridge_init(struct nwl_pcie *pcie)
 	nwl_bridge_writel(pcie, CFG_ENABLE_MSG_FILTER_MASK,
 			  BRCFG_PCIE_RX_MSG_FILTER);
 
+	/* This routes the PCIe DMA traffic to go through CCI path */
+	if (of_dma_is_coherent(dev->of_node))
+		nwl_bridge_writel(pcie, nwl_bridge_readl(pcie, BRCFG_PCIE_RX1) |
+				  CFG_PCIE_CACHE, BRCFG_PCIE_RX1);
+
 	err = nwl_wait_for_link(pcie);
 	if (err)
 		return err;