serial: 8250_bcm2835aux: Fix clock imbalance in PM resume

During review Ulf Hansson discovered a clock imbalance in the recently
introduced PM resume code. The driver should enable the clock only in
case it has been disabled in suspend before. In order to make the
conditions easier to read, refactor this into a separate function.
Reported-by: Ulf Hansson <ulf.hansson@linaro.org>
Closes: https://lore.kernel.org/linux-arm-kernel/CAPDyKFoJh3j8xSeXZ9o031YZLTCDYVA+dgvURuwozjDpU_aauA@mail.gmail.com/
Fixes: 0e1d8780 ("serial: 8250_bcm2835aux: add PM suspend/resume support")
Signed-off-by: Stefan Wahren <wahrenst@gmx.net>
Link: https://lore.kernel.org/r/20240818174936.88372-1-wahrenst@gmx.netSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/8250/8250_bcm2835aux.c

@@ -214,17 +214,27 @@ static const struct acpi_device_id bcm2835aux_serial_acpi_match[] = {
 };
 MODULE_DEVICE_TABLE(acpi, bcm2835aux_serial_acpi_match);
 
-static int bcm2835aux_suspend(struct device *dev)
+static bool bcm2835aux_can_disable_clock(struct device *dev)
 {
 	struct bcm2835aux_data *data = dev_get_drvdata(dev);
 	struct uart_8250_port *up = serial8250_get_port(data->line);
 
-	serial8250_suspend_port(data->line);
-
 	if (device_may_wakeup(dev))
-		return 0;
+		return false;
 
 	if (uart_console(&up->port) && !console_suspend_enabled)
+		return false;
+
+	return true;
+}
+
+static int bcm2835aux_suspend(struct device *dev)
+{
+	struct bcm2835aux_data *data = dev_get_drvdata(dev);
+
+	serial8250_suspend_port(data->line);
+
+	if (!bcm2835aux_can_disable_clock(dev))
 		return 0;
 
 	clk_disable_unprepare(data->clk);
@@ -236,9 +246,11 @@ static int bcm2835aux_resume(struct device *dev)
 	struct bcm2835aux_data *data = dev_get_drvdata(dev);
 	int ret;
 
-	ret = clk_prepare_enable(data->clk);
-	if (ret)
-		return ret;
+	if (bcm2835aux_can_disable_clock(dev)) {
+		ret = clk_prepare_enable(data->clk);
+		if (ret)
+			return ret;
+	}
 
 	serial8250_resume_port(data->line);