[PATCH v4] serial: 8250-mtk: modify mtk uart power and clock management

[Changqi Hu <changqi.hu@xxxxxxxxxxxx>]

MTK uart design no need to control uart clock,
so we just control bus clock in runtime function.
Add uart clock used count to avoid repeatedly switching the clock.

Signed-off-by: Changqi Hu <changqi.hu@xxxxxxxxxxxx>
---

Changes in v4:
 Modify commit-message

Changes in v3:
 Merge patch v1 and v2 together.
 
Changes in v2:
 Enable uart bus clock when probe and resume base on v1 patch,
 but miss v1 patch itself.

 drivers/tty/serial/8250/8250_mtk.c | 50 ++++++++++++++++++++++++--------------
 1 file changed, 32 insertions(+), 18 deletions(-)

diff --git a/drivers/tty/serial/8250/8250_mtk.c b/drivers/tty/serial/8250/8250_mtk.c
index 4d067f5..f839380 100644
--- a/drivers/tty/serial/8250/8250_mtk.c
+++ b/drivers/tty/serial/8250/8250_mtk.c
@@ -32,6 +32,7 @@
 #define MTK_UART_RXTRI_AD	0x14	/* RX Trigger address */
 #define MTK_UART_FRACDIV_L	0x15	/* Fractional divider LSB address */
 #define MTK_UART_FRACDIV_M	0x16	/* Fractional divider MSB address */
+#define MTK_UART_DEBUG0	0x18
 #define MTK_UART_IER_XOFFI	0x20	/* Enable XOFF character interrupt */
 #define MTK_UART_IER_RTSI	0x40	/* Enable RTS Modem status interrupt */
 #define MTK_UART_IER_CTSI	0x80	/* Enable CTS Modem status interrupt */
@@ -388,9 +389,18 @@ mtk8250_set_termios(struct uart_port *port, struct ktermios *termios,
 static int __maybe_unused mtk8250_runtime_suspend(struct device *dev)
 {
 	struct mtk8250_data *data = dev_get_drvdata(dev);
+	struct uart_8250_port *up = serial8250_get_port(data->line);
 
-	clk_disable_unprepare(data->uart_clk);
-	clk_disable_unprepare(data->bus_clk);
+	/* wait until UART in idle status */
+	while
+		(serial_in(up, MTK_UART_DEBUG0));
+
+	if (data->clk_count == 0U) {
+		dev_dbg(dev, "%s clock count is 0\n", __func__);
+	} else {
+		clk_disable_unprepare(data->bus_clk);
+		data->clk_count--;
+	}
 
 	return 0;
 }
@@ -400,16 +410,16 @@ static int __maybe_unused mtk8250_runtime_resume(struct device *dev)
 	struct mtk8250_data *data = dev_get_drvdata(dev);
 	int err;
 
-	err = clk_prepare_enable(data->uart_clk);
-	if (err) {
-		dev_warn(dev, "Can't enable clock\n");
-		return err;
-	}
-
-	err = clk_prepare_enable(data->bus_clk);
-	if (err) {
-		dev_warn(dev, "Can't enable bus clock\n");
-		return err;
+	if (data->clk_count > 0U) {
+		dev_dbg(dev, "%s clock count is %d\n", __func__,
+			data->clk_count);
+	} else {
+		err = clk_prepare_enable(data->bus_clk);
+		if (err) {
+			dev_warn(dev, "Can't enable bus clock\n");
+			return err;
+		}
+		data->clk_count++;
 	}
 
 	return 0;
@@ -419,12 +429,14 @@ static void
 mtk8250_do_pm(struct uart_port *port, unsigned int state, unsigned int old)
 {
 	if (!state)
-		pm_runtime_get_sync(port->dev);
+		if (!mtk8250_runtime_resume(port->dev))
+			pm_runtime_get_sync(port->dev);
 
 	serial8250_do_pm(port, state, old);
 
 	if (state)
-		pm_runtime_put_sync_suspend(port->dev);
+		if (!pm_runtime_put_sync_suspend(port->dev))
+			mtk8250_runtime_suspend(port->dev);
 }
 
 #ifdef CONFIG_SERIAL_8250_DMA
@@ -501,6 +513,8 @@ static int mtk8250_probe(struct platform_device *pdev)
 	if (!data)
 		return -ENOMEM;
 
+	data->clk_count = 0;
+
 	if (pdev->dev.of_node) {
 		err = mtk8250_probe_of(pdev, &uart.port, data);
 		if (err)
@@ -533,6 +547,7 @@ static int mtk8250_probe(struct platform_device *pdev)
 
 	platform_set_drvdata(pdev, data);
 
+	pm_runtime_enable(&pdev->dev);
 	err = mtk8250_runtime_resume(&pdev->dev);
 	if (err)
 		return err;
@@ -541,9 +556,6 @@ static int mtk8250_probe(struct platform_device *pdev)
 	if (data->line < 0)
 		return data->line;
 
-	pm_runtime_set_active(&pdev->dev);
-	pm_runtime_enable(&pdev->dev);
-
 	data->rx_wakeup_irq = platform_get_irq_optional(pdev, 1);
 
 	return 0;
@@ -556,11 +568,13 @@ static int mtk8250_remove(struct platform_device *pdev)
 	pm_runtime_get_sync(&pdev->dev);
 
 	serial8250_unregister_port(data->line);
-	mtk8250_runtime_suspend(&pdev->dev);
 
 	pm_runtime_disable(&pdev->dev);
 	pm_runtime_put_noidle(&pdev->dev);
 
+	if (!pm_runtime_status_suspended(&pdev->dev))
+		mtk8250_runtime_suspend(&pdev->dev);
+
 	return 0;
 }
 
-- 
2.6.4