serial: msm: Use OPP table for DVFS support

Parse the OPP table from the device tree and use dev_pm_opp_set_rate()
instead of clk_set_rate() to allow making performance state votes
specified in the OPP table (e.g. for power domains and interconnects).

Without an OPP table in the device tree this will behave just as before
this patch.
Signed-off-by: Stephan Gerhold <stephan.gerhold@kernkonzept.com>
Link: https://lore.kernel.org/r/20231128-serial-msm-dvfs-v1-2-4f290d20a4be@kernkonzept.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/msm_serial.c

@@ -24,6 +24,7 @@
 #include <linux/slab.h>
 #include <linux/clk.h>
 #include <linux/platform_device.h>
+#include <linux/pm_opp.h>
 #include <linux/delay.h>
 #include <linux/of.h>
 #include <linux/of_device.h>
@@ -1131,7 +1132,7 @@ static int msm_set_baud_rate(struct uart_port *port, unsigned int baud,
 	uart_port_unlock_irqrestore(port, flags);
 
 	entry = msm_find_best_baud(port, baud, &rate);
-	clk_set_rate(msm_port->clk, rate);
+	dev_pm_opp_set_rate(port->dev, rate);
 	baud = rate / 16 / entry->divisor;
 
 	uart_port_lock_irqsave(port, &flags);
@@ -1186,6 +1187,7 @@ static void msm_init_clock(struct uart_port *port)
 {
 	struct msm_port *msm_port = to_msm_port(port);
 
+	dev_pm_opp_set_rate(port->dev, port->uartclk);
 	clk_prepare_enable(msm_port->clk);
 	clk_prepare_enable(msm_port->pclk);
 	msm_serial_set_mnd_regs(port);
@@ -1239,6 +1241,7 @@ static int msm_startup(struct uart_port *port)
 
 	clk_disable_unprepare(msm_port->pclk);
 	clk_disable_unprepare(msm_port->clk);
+	dev_pm_opp_set_rate(port->dev, 0);
 
 	return ret;
 }
@@ -1254,6 +1257,7 @@ static void msm_shutdown(struct uart_port *port)
 		msm_release_dma(msm_port);
 
 	clk_disable_unprepare(msm_port->clk);
+	dev_pm_opp_set_rate(port->dev, 0);
 
 	free_irq(port->irq, port);
 }
@@ -1419,11 +1423,13 @@ static void msm_power(struct uart_port *port, unsigned int state,
 
 	switch (state) {
 	case 0:
+		dev_pm_opp_set_rate(port->dev, port->uartclk);
 		clk_prepare_enable(msm_port->clk);
 		clk_prepare_enable(msm_port->pclk);
 		break;
 	case 3:
 		clk_disable_unprepare(msm_port->clk);
+		dev_pm_opp_set_rate(port->dev, 0);
 		clk_disable_unprepare(msm_port->pclk);
 		break;
 	default:
@@ -1789,7 +1795,7 @@ static int msm_serial_probe(struct platform_device *pdev)
 	struct resource *resource;
 	struct uart_port *port;
 	const struct of_device_id *id;
-	int irq, line;
+	int irq, line, ret;
 
 	if (pdev->dev.of_node)
 		line = of_alias_get_id(pdev->dev.of_node, "serial");
@@ -1824,6 +1830,15 @@ static int msm_serial_probe(struct platform_device *pdev)
 			return PTR_ERR(msm_port->pclk);
 	}
 
+	ret = devm_pm_opp_set_clkname(&pdev->dev, "core");
+	if (ret)
+		return ret;
+
+	/* OPP table is optional */
+	ret = devm_pm_opp_of_add_table(&pdev->dev);
+	if (ret && ret != -ENODEV)
+		return dev_err_probe(&pdev->dev, ret, "invalid OPP table\n");
+
 	port->uartclk = clk_get_rate(msm_port->clk);
 	dev_info(&pdev->dev, "uartclk = %d\n", port->uartclk);