i2c: lpi2c: Avoid calling clk_get_rate during transfer

Instead of repeatedly calling clk_get_rate for each transfer, lock
the clock rate and cache the value.
A deadlock has been observed while adding tlv320aic32x4 audio codec to
the system. When this clock provider adds its clock, the clk mutex is
locked already, it needs to access i2c, which in return needs the mutex
for clk_get_rate as well.
Signed-off-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Reviewed-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Reviewed-by: Andi Shyti <andi.shyti@kernel.org>
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>

drivers/i2c/busses/i2c-imx-lpi2c.c

@@ -99,6 +99,7 @@ struct lpi2c_imx_struct {
 	__u8			*rx_buf;
 	__u8			*tx_buf;
 	struct completion	complete;
+	unsigned long		rate_per;
 	unsigned int		msglen;
 	unsigned int		delivered;
 	unsigned int		block_data;
@@ -212,9 +213,7 @@ static int lpi2c_imx_config(struct lpi2c_imx_struct *lpi2c_imx)
 
 	lpi2c_imx_set_mode(lpi2c_imx);
 
-	clk_rate = clk_get_rate(lpi2c_imx->clks[0].clk);
-	if (!clk_rate)
-		return -EINVAL;
+	clk_rate = lpi2c_imx->rate_per;
 
 	if (lpi2c_imx->mode == HS || lpi2c_imx->mode == ULTRA_FAST)
 		filt = 0;
@@ -611,6 +610,20 @@ static int lpi2c_imx_probe(struct platform_device *pdev)
 	if (ret)
 		return ret;
 
+	/*
+	 * Lock the parent clock rate to avoid getting parent clock upon
+	 * each transfer
+	 */
+	ret = devm_clk_rate_exclusive_get(&pdev->dev, lpi2c_imx->clks[0].clk);
+	if (ret)
+		return dev_err_probe(&pdev->dev, ret,
+				     "can't lock I2C peripheral clock rate\n");
+
+	lpi2c_imx->rate_per = clk_get_rate(lpi2c_imx->clks[0].clk);
+	if (!lpi2c_imx->rate_per)
+		return dev_err_probe(&pdev->dev, -EINVAL,
+				     "can't get I2C peripheral clock rate\n");
+
 	pm_runtime_set_autosuspend_delay(&pdev->dev, I2C_PM_TIMEOUT);
 	pm_runtime_use_autosuspend(&pdev->dev);
 	pm_runtime_get_noresume(&pdev->dev);