ARM: 8906/1: drivers/amba: add reset control to amba bus probe

The primecell controller on some SoCs, i.e. SoCFPGA, is held in reset
by default. Until recently, the DMA controller was brought out of reset by the bootloader(i.e. U-Boot). But a recent change in U-Boot, the peripherals that are not used are held in reset and are left to Linux to bring them out of reset.

Add a mechanism for getting the reset property and de-assert the primecell module from reset if found. This is a not a hard fail if the reset property is not present in the device tree node, so the driver will continue to probe.

Because there are different variants of the controller that may have
multiple reset signals, the code will find all reset(s) specified and
de-assert them.

Signed-off-by: Dinh Nguyen <dinguyen@kernel.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Philipp Zabel <p.zabel@pengutronix.de>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>

drivers/amba/bus.c

@@ -18,6 +18,7 @@
 #include <linux/limits.h>
 #include <linux/clk/clk-conf.h>
 #include <linux/platform_device.h>
+#include <linux/reset.h>
 
 #include <asm/irq.h>
 
@@ -401,6 +402,19 @@ static int amba_device_try_add(struct amba_device *dev, struct resource *parent)
 	ret = amba_get_enable_pclk(dev);
 	if (ret == 0) {
 		u32 pid, cid;
+		struct reset_control *rstc;
+
+		/*
+		 * Find reset control(s) of the amba bus and de-assert them.
+		 */
+		rstc = of_reset_control_array_get_optional_shared(dev->dev.of_node);
+		if (IS_ERR(rstc)) {
+			if (PTR_ERR(rstc) != -EPROBE_DEFER)
+				dev_err(&dev->dev, "Can't get amba reset!\n");
+			return PTR_ERR(rstc);
+		}
+		reset_control_deassert(rstc);
+		reset_control_put(rstc);
 
 		/*
 		 * Read pid and cid based on size of resource