PCI: armada8k: Fix clock resource by adding a register clock

On Armada 7K/8K we need to explicitly enable the register clock. This
clock is optional because not all the SoCs using this IP need it but at
least for Armada 7K/8K it is actually mandatory.

The binding documentation is updated accordingly.

Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>

Documentation/devicetree/bindings/pci/pci-armada8k.txt

@@ -12,7 +12,10 @@ Required properties:
    - "ctrl" for the control register region
    - "config" for the config space region
 - interrupts: Interrupt specifier for the PCIe controler
-- clocks: reference to the PCIe controller clock
+- clocks: reference to the PCIe controller clocks
+- clock-names: mandatory if there is a second clock, in this case the
+   name must be "core" for the first clock and "reg" for the second
+   one
 
 Example:
 

drivers/pci/dwc/pcie-armada8k.c

@@ -28,6 +28,7 @@
 struct armada8k_pcie {
 	struct dw_pcie *pci;
 	struct clk *clk;
+	struct clk *clk_reg;
 };
 
 #define PCIE_VENDOR_REGS_OFFSET		0x8000
@@ -229,23 +230,36 @@ static int armada8k_pcie_probe(struct platform_device *pdev)
 	if (ret)
 		return ret;
 
+	pcie->clk_reg = devm_clk_get(dev, "reg");
+	if (pcie->clk_reg == ERR_PTR(-EPROBE_DEFER)) {
+		ret = -EPROBE_DEFER;
+		goto fail;
+	}
+	if (!IS_ERR(pcie->clk_reg)) {
+		ret = clk_prepare_enable(pcie->clk_reg);
+		if (ret)
+			goto fail_clkreg;
+	}
+
 	/* Get the dw-pcie unit configuration/control registers base. */
 	base = platform_get_resource_byname(pdev, IORESOURCE_MEM, "ctrl");
 	pci->dbi_base = devm_pci_remap_cfg_resource(dev, base);
 	if (IS_ERR(pci->dbi_base)) {
 		dev_err(dev, "couldn't remap regs base %p\n", base);
 		ret = PTR_ERR(pci->dbi_base);
-		goto fail;
+		goto fail_clkreg;
 	}
 
 	platform_set_drvdata(pdev, pcie);
 
 	ret = armada8k_add_pcie_port(pcie, pdev);
 	if (ret)
-		goto fail;
+		goto fail_clkreg;
 
 	return 0;
 
+fail_clkreg:
+	clk_disable_unprepare(pcie->clk_reg);
 fail:
 	clk_disable_unprepare(pcie->clk);