i2c: tegra: Use reset_control_reset()

Use a single reset_control_reset() instead of assert/deasset couple in
order to make code cleaner a tad. Note that the reset_control_reset()
uses 1 microsecond delay instead of 2 that was used previously, but this
shouldn't matter because one microsecond is a default reset time for most
of Tegra peripherals and TRM doesn't mention anything special in regards
to I2C controller's reset propagation time.

In addition don't ignore potential error of the reset control by emitting
a noisy warning if it fails, which will indicate an existence of a severe
problem, while still allow machine to boot up.
Reviewed-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Acked-by: Thierry Reding <treding@nvidia.com>
Tested-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>

drivers/i2c/busses/i2c-tegra.c

@@ -785,9 +785,16 @@ static int tegra_i2c_init(struct tegra_i2c_dev *i2c_dev)
 	u32 tsu_thd;
 	u8 tlow, thigh;
 
-	reset_control_assert(i2c_dev->rst);
-	udelay(2);
-	reset_control_deassert(i2c_dev->rst);
+	/*
+	 * The reset shouldn't ever fail in practice. The failure will be a
+	 * sign of a severe problem that needs to be resolved. Still we don't
+	 * want to fail the initialization completely because this may break
+	 * kernel boot up since voltage regulators use I2C. Hence, we will
+	 * emit a noisy warning on error, which won't stay unnoticed and
+	 * won't hose machine entirely.
+	 */
+	err = reset_control_reset(i2c_dev->rst);
+	WARN_ON_ONCE(err);
 
 	if (i2c_dev->is_dvc)
 		tegra_dvc_init(i2c_dev);