i2c: cadence: Add reset controller support

The Cadence I2C controller has an external reset signal that needs to be
de-asserted before the I2C controller can be used.

Add support to the driver to be able to take the peripheral out of reset
using the reset controller API. The reset is optional in the driver for
compatibility to systems where the reset managed by the bootloader.
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Acked-by: Michal Simek <michal.simek@amd.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>

drivers/i2c/busses/i2c-cadence.c

@@ -16,6 +16,7 @@
 #include <linux/of.h>
 #include <linux/pm_runtime.h>
 #include <linux/pinctrl/consumer.h>
+#include <linux/reset.h>
 
 /* Register offsets for the I2C device. */
 #define CDNS_I2C_CR_OFFSET		0x00 /* Control Register, RW */
@@ -178,6 +179,7 @@ enum cdns_i2c_slave_state {
  * @bus_hold_flag:	Flag used in repeated start for clearing HOLD bit
  * @clk:		Pointer to struct clk
  * @clk_rate_change_nb:	Notifier block for clock rate changes
+ * @reset:		Reset control for the device
  * @quirks:		flag for broken hold bit usage in r1p10
  * @ctrl_reg:		Cached value of the control register.
  * @ctrl_reg_diva_divb: value of fields DIV_A and DIV_B from CR register
@@ -204,6 +206,7 @@ struct cdns_i2c {
 	unsigned int bus_hold_flag;
 	struct clk *clk;
 	struct notifier_block clk_rate_change_nb;
+	struct reset_control *reset;
 	u32 quirks;
 	u32 ctrl_reg;
 	struct i2c_bus_recovery_info rinfo;
@@ -1325,10 +1328,22 @@ static int cdns_i2c_probe(struct platform_device *pdev)
 		return dev_err_probe(&pdev->dev, PTR_ERR(id->clk),
 				     "input clock not found.\n");
 
+	id->reset = devm_reset_control_get_optional_shared(&pdev->dev, NULL);
+	if (IS_ERR(id->reset))
+		return dev_err_probe(&pdev->dev, PTR_ERR(id->reset),
+				     "Failed to request reset.\n");
+
 	ret = clk_prepare_enable(id->clk);
 	if (ret)
 		dev_err(&pdev->dev, "Unable to enable clock.\n");
 
+	ret = reset_control_deassert(id->reset);
+	if (ret) {
+		dev_err_probe(&pdev->dev, ret,
+			      "Failed to de-assert reset.\n");
+		goto err_clk_dis;
+	}
+
 	pm_runtime_set_autosuspend_delay(id->dev, CNDS_I2C_PM_TIMEOUT);
 	pm_runtime_use_autosuspend(id->dev);
 	pm_runtime_set_active(id->dev);
@@ -1360,28 +1375,30 @@ static int cdns_i2c_probe(struct platform_device *pdev)
 	if (ret) {
 		dev_err(&pdev->dev, "invalid SCL clock: %u Hz\n", id->i2c_clk);
 		ret = -EINVAL;
-		goto err_clk_dis;
+		goto err_clk_notifier_unregister;
 	}
 
 	ret = devm_request_irq(&pdev->dev, irq, cdns_i2c_isr, 0,
 				 DRIVER_NAME, id);
 	if (ret) {
 		dev_err(&pdev->dev, "cannot get irq %d\n", irq);
-		goto err_clk_dis;
+		goto err_clk_notifier_unregister;
 	}
 	cdns_i2c_init(id);
 
 	ret = i2c_add_adapter(&id->adap);
 	if (ret < 0)
-		goto err_clk_dis;
+		goto err_clk_notifier_unregister;
 
 	dev_info(&pdev->dev, "%u kHz mmio %08lx irq %d\n",
 		 id->i2c_clk / 1000, (unsigned long)r_mem->start, irq);
 
 	return 0;
 
-err_clk_dis:
+err_clk_notifier_unregister:
 	clk_notifier_unregister(id->clk, &id->clk_rate_change_nb);
+	reset_control_assert(id->reset);
+err_clk_dis:
 	clk_disable_unprepare(id->clk);
 	pm_runtime_disable(&pdev->dev);
 	pm_runtime_set_suspended(&pdev->dev);
@@ -1406,6 +1423,7 @@ static int cdns_i2c_remove(struct platform_device *pdev)
 
 	i2c_del_adapter(&id->adap);
 	clk_notifier_unregister(id->clk, &id->clk_rate_change_nb);
+	reset_control_assert(id->reset);
 	clk_disable_unprepare(id->clk);
 
 	return 0;