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From: Bastien Curutchet <bastien.curutchet@bootlin.com>
To: bastien.curutchet@bootlin.com,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Jiri Slaby <jirislaby@kernel.org>
Cc: linux-kernel@vger.kernel.org,
	linux-serial@vger.kernel.org,
	Thomas Petazzoni <thomas.petazzoni@bootlin.com>,
	herve.codina@bootlin.com,
	christophercordahi@nanometrics.ca
Subject: [PATCH 1/1] serial: 8250_of: Add clock_notifier
Date: Thu,  4 Apr 2024 09:44:50 +0200
Message-ID: <20240404074450.42708-1-bastien.curutchet@bootlin.com>
Precedence: bulk
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit

The UART's input clock rate can change at runtime but this is not
handled by the driver.

Add a clock_notifier callback that updates the divisors when the input
clock is updated. The serial8250_update_uartclk() is used to do so.
PRE_RATE_CHANGE and ABORT_RATE_CHANGE notifications are ignored, only
the POST_RATE_CHANGE is used.

Reorder the #include to match alphabetic order.

It has been tested on a DAVINCI/OMAP-L138 processor.

Signed-off-by: Bastien Curutchet <bastien.curutchet@bootlin.com>
---
 drivers/tty/serial/8250/8250_of.c | 48 ++++++++++++++++++++++++++++---
 1 file changed, 44 insertions(+), 4 deletions(-)

diff --git a/drivers/tty/serial/8250/8250_of.c b/drivers/tty/serial/8250/8250_of.c
index 5d1dd992d8fb..6d570164d906 100644
--- a/drivers/tty/serial/8250/8250_of.c
+++ b/drivers/tty/serial/8250/8250_of.c
@@ -6,18 +6,19 @@
  */
 
 #include <linux/bits.h>
+#include <linux/clk.h>
 #include <linux/console.h>
 #include <linux/math.h>
 #include <linux/module.h>
-#include <linux/slab.h>
-#include <linux/serial_core.h>
-#include <linux/serial_reg.h>
+#include <linux/notifier.h>
 #include <linux/of_address.h>
 #include <linux/of_irq.h>
 #include <linux/of_platform.h>
 #include <linux/pm_runtime.h>
-#include <linux/clk.h>
 #include <linux/reset.h>
+#include <linux/serial_core.h>
+#include <linux/serial_reg.h>
+#include <linux/slab.h>
 
 #include "8250.h"
 
@@ -26,6 +27,7 @@ struct of_serial_info {
 	struct reset_control *rst;
 	int type;
 	int line;
+	struct notifier_block clk_notifier;
 };
 
 /* Nuvoton NPCM timeout register */
@@ -58,6 +60,29 @@ static int npcm_setup(struct uart_port *port)
 	return 0;
 }
 
+static inline struct of_serial_info *clk_nb_to_info(struct notifier_block *nb)
+{
+	return container_of(nb, struct of_serial_info, clk_notifier);
+}
+
+static int of_platform_serial_clk_notifier_cb(struct notifier_block *nb, unsigned long event,
+					      void *data)
+{
+	struct of_serial_info *info = clk_nb_to_info(nb);
+	struct uart_8250_port *port8250 = serial8250_get_port(info->line);
+	struct clk_notifier_data *ndata = data;
+
+	if (IS_ERR(info->clk))
+		return NOTIFY_DONE;
+
+	if (event == POST_RATE_CHANGE) {
+		serial8250_update_uartclk(&port8250->port, ndata->new_rate);
+		return NOTIFY_OK;
+	}
+
+	return NOTIFY_DONE;
+}
+
 /*
  * Fill a struct uart_port for a given device node
  */
@@ -218,7 +243,19 @@ static int of_platform_serial_probe(struct platform_device *ofdev)
 	info->type = port_type;
 	info->line = ret;
 	platform_set_drvdata(ofdev, info);
+
+	if (info->clk) {
+		info->clk_notifier.notifier_call = of_platform_serial_clk_notifier_cb;
+		ret = clk_notifier_register(info->clk, &info->clk_notifier);
+		if (ret) {
+			dev_err_probe(port8250.port.dev, ret, "Failed to set the clock notifier\n");
+			goto err_unregister;
+		}
+	}
+
 	return 0;
+err_unregister:
+	serial8250_unregister_port(info->line);
 err_dispose:
 	pm_runtime_put_sync(&ofdev->dev);
 	pm_runtime_disable(&ofdev->dev);
@@ -234,6 +271,9 @@ static void of_platform_serial_remove(struct platform_device *ofdev)
 {
 	struct of_serial_info *info = platform_get_drvdata(ofdev);
 
+	if (info->clk)
+		clk_notifier_unregister(info->clk, &info->clk_notifier);
+
 	serial8250_unregister_port(info->line);
 
 	reset_control_assert(info->rst);
-- 
2.44.0