i2c: stm32f7: Do not prepare/unprepare clock during runtime suspend/resume

In case there is any sort of clock controller attached to this I2C bus
controller, for example Versaclock or even an AIC32x4 I2C codec, then
an I2C transfer triggered from the clock controller clk_ops .prepare
callback may trigger a deadlock on drivers/clk/clk.c prepare_lock mutex.

This is because the clock controller first grabs the prepare_lock mutex
and then performs the prepare operation, including its I2C access. The
I2C access resumes this I2C bus controller via .runtime_resume callback,
which calls clk_prepare_enable(), which attempts to grab the prepare_lock
mutex again and deadlocks.

Since the clock are already prepared since probe() and unprepared in
remove(), use simple clk_enable()/clk_disable() calls to enable and
disable the clock on runtime suspend and resume, to avoid hitting the
prepare_lock mutex.
Acked-by: Alain Volmat <alain.volmat@foss.st.com>
Signed-off-by: Marek Vasut <marex@denx.de>
Fixes: 4e7bca6f ("i2c: i2c-stm32f7: add PM Runtime support")
Cc: <stable@vger.kernel.org> # v5.0+
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>

drivers/i2c/busses/i2c-stm32f7.c

@@ -2395,7 +2395,7 @@ static int __maybe_unused stm32f7_i2c_runtime_suspend(struct device *dev)
 	struct stm32f7_i2c_dev *i2c_dev = dev_get_drvdata(dev);
 
 	if (!stm32f7_i2c_is_slave_registered(i2c_dev))
-		clk_disable_unprepare(i2c_dev->clk);
+		clk_disable(i2c_dev->clk);
 
 	return 0;
 }
@@ -2406,9 +2406,9 @@ static int __maybe_unused stm32f7_i2c_runtime_resume(struct device *dev)
 	int ret;
 
 	if (!stm32f7_i2c_is_slave_registered(i2c_dev)) {
-		ret = clk_prepare_enable(i2c_dev->clk);
+		ret = clk_enable(i2c_dev->clk);
 		if (ret) {
-			dev_err(dev, "failed to prepare_enable clock\n");
+			dev_err(dev, "failed to enable clock\n");
 			return ret;
 		}
 	}