[PATCH v3] i2c: aspeed: Deassert reset in probe

[Joel Stanley <joel@jms.id.au>]

In order to use i2c from a cold boot, the i2c peripheral must be taken
out of reset. We request a shared reset controller each time a bus
driver is loaded, as the reset is shared between the 14 i2c buses.

On remove the reset is asserted, which only touches the hardware once
the last i2c bus is removed.

The request is optional, so if a device tree does not specify a reset
controller (or the driver is not built in), the driver continues to
probe.

Reviewed-by: Brendan Higgins <brendanhiggins@google.com>
Reviewed-by: Philipp Zabel <philipp.zabel@gmail.com>
Signed-off-by: Joel Stanley <joel@jms.id.au>
---
v3: Check for bad reset controller probe (caused by eg. bad device tree)
    and set ->rst to NULL so assert/desassert does not cause a warning to
    be printed
v2: Sort the headers
---
 drivers/i2c/busses/i2c-aspeed.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/i2c/busses/i2c-aspeed.c b/drivers/i2c/busses/i2c-aspeed.c
index 284f8670dbeb..5dec00d663eb 100644
--- a/drivers/i2c/busses/i2c-aspeed.c
+++ b/drivers/i2c/busses/i2c-aspeed.c
@@ -12,6 +12,7 @@
 
 #include <linux/clk.h>
 #include <linux/completion.h>
+#include <linux/delay.h>
 #include <linux/err.h>
 #include <linux/errno.h>
 #include <linux/i2c.h>
@@ -27,6 +28,7 @@
 #include <linux/of_irq.h>
 #include <linux/of_platform.h>
 #include <linux/platform_device.h>
+#include <linux/reset.h>
 #include <linux/slab.h>
 
 /* I2C Register */
@@ -132,6 +134,7 @@ struct aspeed_i2c_bus {
 	struct i2c_adapter		adap;
 	struct device			*dev;
 	void __iomem			*base;
+	struct reset_control		*rst;
 	/* Synchronizes I/O mem access to base. */
 	spinlock_t			lock;
 	struct completion		cmd_complete;
@@ -847,6 +850,13 @@ static int aspeed_i2c_probe_bus(struct platform_device *pdev)
 	/* We just need the clock rate, we don't actually use the clk object. */
 	devm_clk_put(&pdev->dev, parent_clk);
 
+	bus->rst = devm_reset_control_get_optional_shared(&pdev->dev, NULL);
+	if (IS_ERR(bus->rst)) {
+		dev_err(&pdev->dev, "invalid reset controller in device tree");
+		bus->rst = NULL;
+	} else
+		reset_control_deassert(bus->rst);
+
 	ret = of_property_read_u32(pdev->dev.of_node,
 				   "bus-frequency", &bus->bus_frequency);
 	if (ret < 0) {
@@ -919,6 +929,8 @@ static int aspeed_i2c_remove_bus(struct platform_device *pdev)
 
 	i2c_del_adapter(&bus->adap);
 
+	reset_control_assert(bus->rst);
+
 	return 0;
 }
 
-- 
2.14.1