spi: take the SPI IO-mutex in the spi_set_cs_timing method

this patch takes the io_mutex to prevent an unprotected HW
register modification in the set_cs_timing callback.

Fixes: 4cea6b8c ("spi: add power control when set_cs_timing")
Signed-off-by: Leilk Liu <leilk.liu@mediatek.com>
Link: https://lore.kernel.org/r/20210508060214.1485-1-leilk.liu@mediatek.comSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi.c

@@ -3457,9 +3457,12 @@ int spi_set_cs_timing(struct spi_device *spi, struct spi_delay *setup,
 
 	if (spi->controller->set_cs_timing &&
 	    !(spi->cs_gpiod || gpio_is_valid(spi->cs_gpio))) {
+		mutex_lock(&spi->controller->io_mutex);
+
 		if (spi->controller->auto_runtime_pm) {
 			status = pm_runtime_get_sync(parent);
 			if (status < 0) {
+				mutex_unlock(&spi->controller->io_mutex);
 				pm_runtime_put_noidle(parent);
 				dev_err(&spi->controller->dev, "Failed to power device: %d\n",
 					status);
@@ -3470,11 +3473,13 @@ int spi_set_cs_timing(struct spi_device *spi, struct spi_delay *setup,
 								hold, inactive);
 			pm_runtime_mark_last_busy(parent);
 			pm_runtime_put_autosuspend(parent);
-			return status;
 		} else {
-			return spi->controller->set_cs_timing(spi, setup, hold,
+			status = spi->controller->set_cs_timing(spi, setup, hold,
 							      inactive);
 		}
+
+		mutex_unlock(&spi->controller->io_mutex);
+		return status;
 	}
 
 	if ((setup && setup->unit == SPI_DELAY_UNIT_SCK) ||