i2c: rk3x: Restore clock settings at resume time

Depending on a number of factors including:
- Which exact Rockchip SoC we're working with
- How deep we suspend
- Which i2c port we're on

We might lose the state of the i2c registers at suspend time.
Specifically we've found that on rk3399 the i2c ports that are not in
the PMU power domain lose their state with the current suspend depth
configured by ARM Tursted Firmware.

Note that there are very few actual i2c registers that aren't configured
per transfer anyway so all we actually need to re-configure are the
clock config registers.  We'll just add a call to rk3x_i2c_adapt_div()
at resume time and be done with it.

NOTE: On rk3399 on ports whose power was lost, I put printouts in at
resume time.  I saw things like:
  before: con=0x00010300, div=0x00060006
  after:  con=0x00010200, div=0x00180025
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: David Wu <david.wu@rock-chips.com>
Tested-by: David Wu <david.wu@rock-chips.com>
[wsa: removed duplicate const]
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

drivers/i2c/busses/i2c-rk3x.c

@@ -1111,6 +1111,15 @@ static int rk3x_i2c_xfer(struct i2c_adapter *adap,
 	return ret < 0 ? ret : num;
 }
 
+static __maybe_unused int rk3x_i2c_resume(struct device *dev)
+{
+	struct rk3x_i2c *i2c = dev_get_drvdata(dev);
+
+	rk3x_i2c_adapt_div(i2c, clk_get_rate(i2c->clk));
+
+	return 0;
+}
+
 static u32 rk3x_i2c_func(struct i2c_adapter *adap)
 {
 	return I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL | I2C_FUNC_PROTOCOL_MANGLING;
@@ -1334,12 +1343,15 @@ static int rk3x_i2c_remove(struct platform_device *pdev)
 	return 0;
 }
 
+static SIMPLE_DEV_PM_OPS(rk3x_i2c_pm_ops, NULL, rk3x_i2c_resume);
+
 static struct platform_driver rk3x_i2c_driver = {
 	.probe   = rk3x_i2c_probe,
 	.remove  = rk3x_i2c_remove,
 	.driver  = {
 		.name  = "rk3x-i2c",
 		.of_match_table = rk3x_i2c_match,
+		.pm = &rk3x_i2c_pm_ops,
 	},
 };