PCI: faraday: Add clock handling

Add some optional clock handling to the Faraday FTPCI100.  We just get and
prepare+enable the clocks right now, if they exist.  We can add more
elaborate clock handling later.
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
[bhelgaas: folded in "Make clocks compulsory" fix from
http://lkml.kernel.org/r/20170621085730.28804-1-linus.walleij@linaro.org
Also folded in the clock max/cur speed fixes from
http://lkml.kernel.org/r/20170621162651.25315-1-linus.walleij@linaro.org]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

drivers/pci/host/pci-ftpci100.c

@@ -25,6 +25,7 @@
 #include <linux/irqchip/chained_irq.h>
 #include <linux/bitops.h>
 #include <linux/irq.h>
+#include <linux/clk.h>
 
 /*
  * Special configuration registers directly in the first few words
@@ -37,6 +38,7 @@
 #define PCI_CONFIG	0x28 /* PCI configuration command register */
 #define PCI_DATA	0x2C
 
+#define FARADAY_PCI_STATUS_CMD		0x04 /* Status and command */
 #define FARADAY_PCI_PMC			0x40 /* Power management control */
 #define FARADAY_PCI_PMCSR		0x44 /* Power management status */
 #define FARADAY_PCI_CTRL1		0x48 /* Control register 1 */
@@ -45,6 +47,8 @@
 #define FARADAY_PCI_MEM2_BASE_SIZE	0x54 /* Memory base and size #2 */
 #define FARADAY_PCI_MEM3_BASE_SIZE	0x58 /* Memory base and size #3 */
 
+#define PCI_STATUS_66MHZ_CAPABLE	BIT(21)
+
 /* Bits 31..28 gives INTD..INTA status */
 #define PCI_CTRL2_INTSTS_SHIFT		28
 #define PCI_CTRL2_INTMASK_CMDERR	BIT(27)
@@ -117,6 +121,7 @@ struct faraday_pci {
 	void __iomem *base;
 	struct irq_domain *irqdomain;
 	struct pci_bus *bus;
+	struct clk *bus_clk;
 };
 
 static int faraday_res_to_memcfg(resource_size_t mem_base,
@@ -444,6 +449,9 @@ static int faraday_pci_probe(struct platform_device *pdev)
 	struct resource *mem;
 	struct resource *io;
 	struct pci_host_bridge *host;
+	struct clk *clk;
+	unsigned char max_bus_speed = PCI_SPEED_33MHz;
+	unsigned char cur_bus_speed = PCI_SPEED_33MHz;
 	int ret;
 	u32 val;
 	LIST_HEAD(res);
@@ -462,6 +470,24 @@ static int faraday_pci_probe(struct platform_device *pdev)
 	host->sysdata = p;
 	p->dev = dev;
 
+	/* Retrieve and enable optional clocks */
+	clk = devm_clk_get(dev, "PCLK");
+	if (IS_ERR(clk))
+		return PTR_ERR(clk);
+	ret = clk_prepare_enable(clk);
+	if (ret) {
+		dev_err(dev, "could not prepare PCLK\n");
+		return ret;
+	}
+	p->bus_clk = devm_clk_get(dev, "PCICLK");
+	if (IS_ERR(p->bus_clk))
+		return PTR_ERR(clk);
+	ret = clk_prepare_enable(p->bus_clk);
+	if (ret) {
+		dev_err(dev, "could not prepare PCICLK\n");
+		return ret;
+	}
+
 	regs = platform_get_resource(pdev, IORESOURCE_MEM, 0);
 	p->base = devm_ioremap_resource(dev, regs);
 	if (IS_ERR(p->base))
@@ -524,6 +550,34 @@ static int faraday_pci_probe(struct platform_device *pdev)
 		}
 	}
 
+	/* Check bus clock if we can gear up to 66 MHz */
+	if (!IS_ERR(p->bus_clk)) {
+		unsigned long rate;
+		u32 val;
+
+		faraday_raw_pci_read_config(p, 0, 0,
+					    FARADAY_PCI_STATUS_CMD, 4, &val);
+		rate = clk_get_rate(p->bus_clk);
+
+		if ((rate == 33000000) && (val & PCI_STATUS_66MHZ_CAPABLE)) {
+			dev_info(dev, "33MHz bus is 66MHz capable\n");
+			max_bus_speed = PCI_SPEED_66MHz;
+			ret = clk_set_rate(p->bus_clk, 66000000);
+			if (ret)
+				dev_err(dev, "failed to set bus clock\n");
+		} else {
+			dev_info(dev, "33MHz only bus\n");
+			max_bus_speed = PCI_SPEED_33MHz;
+		}
+
+		/* Bumping the clock may fail so read back the rate */
+		rate = clk_get_rate(p->bus_clk);
+		if (rate == 33000000)
+			cur_bus_speed = PCI_SPEED_33MHz;
+		if (rate == 66000000)
+			cur_bus_speed = PCI_SPEED_66MHz;
+	}
+
 	ret = faraday_pci_parse_map_dma_ranges(p, dev->of_node);
 	if (ret)
 		return ret;
@@ -535,6 +589,8 @@ static int faraday_pci_probe(struct platform_device *pdev)
 		return ret;
 	}
 	p->bus = host->bus;
+	p->bus->max_bus_speed = max_bus_speed;
+	p->bus->cur_bus_speed = cur_bus_speed;
 
 	pci_bus_assign_resources(p->bus);
 	pci_bus_add_devices(p->bus);