PCI: cadence: Clear FLR in device capabilities register

Clear FLR (Function Level Reset) from device capabilities
registers for all physical functions.

During FLR, the Margining Lane Status and Margining Lane Control
registers should not be reset, as per PCIe specification.
However, the controller incorrectly resets these registers upon FLR.
This causes PCISIG compliance FLR test to fail. Hence preventing
all functions from advertising FLR support if flag quirk_disable_flr
is set.

Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Parshuram Thombare <[e-mail]>
Signed-off-by: Lorenzo Pieralisi <[e-mail]>

drivers/pci/controller/cadence/pci-j721e.c

···
 	enum j721e_pcie_mode	mode;
 	unsigned int		quirk_retrain_flag:1;
 	unsigned int		quirk_detect_quiet_flag:1;
+	unsigned int		quirk_disable_flr:1;
 	u32			linkdown_irq_regfield;
 	unsigned int		byte_access_allowed:1;
 };
···
 static const struct j721e_pcie_data j7200_pcie_ep_data = {
 	.mode = PCI_MODE_EP,
 	.quirk_detect_quiet_flag = true,
+	.quirk_disable_flr = true,
 };
 
 static const struct j721e_pcie_data am64_pcie_rc_data = {
···
 			return -ENOMEM;
 
 		ep->quirk_detect_quiet_flag = data->quirk_detect_quiet_flag;
+		ep->quirk_disable_flr = data->quirk_disable_flr;
 
 		cdns_pcie = &ep->pcie;
 		cdns_pcie->dev = dev;

drivers/pci/controller/cadence/pcie-cadence-ep.c

···
 	struct cdns_pcie_ep *ep = epc_get_drvdata(epc);
 	struct cdns_pcie *pcie = &ep->pcie;
 	struct device *dev = pcie->dev;
-	int ret;
+	int max_epfs = sizeof(epc->function_num_map) * 8;
+	int ret, value, epf;
 
 	/*
 	 * BIT(0) is hardwired to 1, hence function 0 is always enabled
 	 * and can't be disabled anyway.
 	 */
 	cdns_pcie_writel(pcie, CDNS_PCIE_LM_EP_FUNC_CFG, epc->function_num_map);
+
+	if (ep->quirk_disable_flr) {
+		for (epf = 0; epf < max_epfs; epf++) {
+			if (!(epc->function_num_map & BIT(epf)))
+				continue;
+
+			value = cdns_pcie_ep_fn_readl(pcie, epf,
+					CDNS_PCIE_EP_FUNC_DEV_CAP_OFFSET +
+					PCI_EXP_DEVCAP);
+			value &= ~PCI_EXP_DEVCAP_FLR;
+			cdns_pcie_ep_fn_writel(pcie, epf,
+					CDNS_PCIE_EP_FUNC_DEV_CAP_OFFSET +
+					PCI_EXP_DEVCAP, value);
+		}
+	}
 
 	ret = cdns_pcie_start_link(pcie);
 	if (ret) {

drivers/pci/controller/cadence/pcie-cadence.h

···
 
 #define CDNS_PCIE_EP_FUNC_MSI_CAP_OFFSET	0x90
 #define CDNS_PCIE_EP_FUNC_MSIX_CAP_OFFSET	0xb0
+#define CDNS_PCIE_EP_FUNC_DEV_CAP_OFFSET	0xc0
 #define CDNS_PCIE_EP_FUNC_SRIOV_CAP_OFFSET	0x200
 
 /*
···
  *        minimize time between read and write
  * @epf: Structure to hold info about endpoint function
  * @quirk_detect_quiet_flag: LTSSM Detect Quiet min delay set as quirk
+ * @quirk_disable_flr: Disable FLR (Function Level Reset) quirk flag
  */
 struct cdns_pcie_ep {
 	struct cdns_pcie	pcie;
···
 	spinlock_t		lock;
 	struct cdns_pcie_epf	*epf;
 	unsigned int		quirk_detect_quiet_flag:1;
+	unsigned int		quirk_disable_flr:1;
 };