gpio: ixp4xx: Handle clock output on pin 14 and 15

This makes it possible to provide basic clock output on pins
14 and 15. The clocks are typically used by random electronics,
not modeled in the device tree, so they just need to be provided
on request.

In order to not disturb old systems that require that the
hardware defaults are kept in the clock setting bits, we only
manipulate these if either device tree property is present.
Once we know a device needs one of the clocks we can set it
in the device tree.

Reviewed-by: Andy Shevchenko <[e-mail]>
Signed-off-by: Linus Walleij <[e-mail]>
Signed-off-by: Bartosz Golaszewski <[e-mail]>

drivers/gpio/gpio-ixp4xx.c

···
 #define IXP4XX_GPIO_STYLE_MASK		GENMASK(2, 0)
 #define IXP4XX_GPIO_STYLE_SIZE		3
 
+/*
+ * Clock output control register defines.
+ */
+#define IXP4XX_GPCLK_CLK0DC_SHIFT	0
+#define IXP4XX_GPCLK_CLK0TC_SHIFT	4
+#define IXP4XX_GPCLK_CLK0_MASK		GENMASK(7, 0)
+#define IXP4XX_GPCLK_MUX14		BIT(8)
+#define IXP4XX_GPCLK_CLK1DC_SHIFT	16
+#define IXP4XX_GPCLK_CLK1TC_SHIFT	20
+#define IXP4XX_GPCLK_CLK1_MASK		GENMASK(23, 16)
+#define IXP4XX_GPCLK_MUX15		BIT(24)
+
 /**
  * struct ixp4xx_gpio - IXP4 GPIO state container
  * @dev: containing device for this instance
···
 	struct ixp4xx_gpio *g;
 	struct gpio_irq_chip *girq;
 	struct device_node *irq_parent;
+	bool clk_14, clk_15;
+	u32 val;
 	int ret;
 
 	g = devm_kzalloc(dev, sizeof(*g), GFP_KERNEL);
···
 	g->fwnode = of_node_to_fwnode(np);
 
 	/*
+	 * If either clock output is enabled explicitly in the device tree
+	 * we take full control of the clock by masking off all bits for
+	 * the clock control and selectively enabling them. Otherwise
+	 * we leave the hardware default settings.
+	 *
+	 * Enable clock outputs with default timings of requested clock.
+	 * If you need control over TC and DC, add these to the device
+	 * tree bindings and use them here.
+	 */
+	clk_14 = of_property_read_bool(np, "intel,ixp4xx-gpio14-clkout");
+	clk_15 = of_property_read_bool(np, "intel,ixp4xx-gpio15-clkout");
+
+	/*
 	 * Make sure GPIO 14 and 15 are NOT used as clocks but GPIO on
 	 * specific machines.
 	 */
 	if (of_machine_is_compatible("dlink,dsm-g600-a") ||
 	    of_machine_is_compatible("iom,nas-100d"))
-		__raw_writel(0x0, g->base + IXP4XX_REG_GPCLK);
+		val = 0;
+	else {
+		val = __raw_readl(g->base + IXP4XX_REG_GPCLK);
+
+		if (clk_14 || clk_15) {
+			val &= ~(IXP4XX_GPCLK_MUX14 | IXP4XX_GPCLK_MUX15);
+			val &= ~IXP4XX_GPCLK_CLK0_MASK;
+			val &= ~IXP4XX_GPCLK_CLK1_MASK;
+			if (clk_14) {
+				/* IXP4XX_GPCLK_CLK0DC implicit low */
+				val |= (1 << IXP4XX_GPCLK_CLK0TC_SHIFT);
+				val |= IXP4XX_GPCLK_MUX14;
+			}
+
+			if (clk_15) {
+				/* IXP4XX_GPCLK_CLK1DC implicit low */
+				val |= (1 << IXP4XX_GPCLK_CLK1TC_SHIFT);
+				val |= IXP4XX_GPCLK_MUX15;
+			}
+		}
+	}
+
+	__raw_writel(val, g->base + IXP4XX_REG_GPCLK);
 
 	/*
 	 * This is a very special big-endian ARM issue: when the IXP4xx is