PCI: designware-ep: Read-only registers need DBI_RO_WR_EN to be writable

Certain registers that pcie-designware-ep tries to write to are read-only
registers. However, these registers can become read/write if we first
enable the DBI_RO_WR_EN bit. Set/unset the DBI_RO_WR_EN bit before/after
writing these registers.
Tested-by: Gustavo Pimentel <gustavo.pimentel@synopsys.com>
Signed-off-by: Niklas Cassel <niklas.cassel@axis.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Acked-by: Joao Pinto <jpinto@synopsys.com>

drivers/pci/dwc/pcie-designware-ep.c

@@ -35,8 +35,10 @@ static void dw_pcie_ep_reset_bar(struct dw_pcie *pci, enum pci_barno bar)
 	u32 reg;
 
 	reg = PCI_BASE_ADDRESS_0 + (4 * bar);
+	dw_pcie_dbi_ro_wr_en(pci);
 	dw_pcie_writel_dbi2(pci, reg, 0x0);
 	dw_pcie_writel_dbi(pci, reg, 0x0);
+	dw_pcie_dbi_ro_wr_dis(pci);
 }
 
 static int dw_pcie_ep_write_header(struct pci_epc *epc,
@@ -45,6 +47,7 @@ static int dw_pcie_ep_write_header(struct pci_epc *epc,
 	struct dw_pcie_ep *ep = epc_get_drvdata(epc);
 	struct dw_pcie *pci = to_dw_pcie_from_ep(ep);
 
+	dw_pcie_dbi_ro_wr_en(pci);
 	dw_pcie_writew_dbi(pci, PCI_VENDOR_ID, hdr->vendorid);
 	dw_pcie_writew_dbi(pci, PCI_DEVICE_ID, hdr->deviceid);
 	dw_pcie_writeb_dbi(pci, PCI_REVISION_ID, hdr->revid);
@@ -58,6 +61,7 @@ static int dw_pcie_ep_write_header(struct pci_epc *epc,
 	dw_pcie_writew_dbi(pci, PCI_SUBSYSTEM_ID, hdr->subsys_id);
 	dw_pcie_writeb_dbi(pci, PCI_INTERRUPT_PIN,
 			   hdr->interrupt_pin);
+	dw_pcie_dbi_ro_wr_dis(pci);
 
 	return 0;
 }
@@ -142,8 +146,10 @@ static int dw_pcie_ep_set_bar(struct pci_epc *epc, enum pci_barno bar,
 	if (ret)
 		return ret;
 
+	dw_pcie_dbi_ro_wr_en(pci);
 	dw_pcie_writel_dbi2(pci, reg, size - 1);
 	dw_pcie_writel_dbi(pci, reg, flags);
+	dw_pcie_dbi_ro_wr_dis(pci);
 
 	return 0;
 }
@@ -223,7 +229,9 @@ static int dw_pcie_ep_set_msi(struct pci_epc *epc, u8 encode_int)
 	val = dw_pcie_readw_dbi(pci, MSI_MESSAGE_CONTROL);
 	val &= ~MSI_CAP_MMC_MASK;
 	val |= (encode_int << MSI_CAP_MMC_SHIFT) & MSI_CAP_MMC_MASK;
+	dw_pcie_dbi_ro_wr_en(pci);
 	dw_pcie_writew_dbi(pci, MSI_MESSAGE_CONTROL, val);
+	dw_pcie_dbi_ro_wr_dis(pci);
 
 	return 0;
 }