2024-04-05 12:06:13

by Bastien Curutchet

Subject: [PATCH v2 1/1] serial: 8250_of: Add clock_notifier

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. Not using PRE_RATE_CHANGE notification can
result in a few corrupted bytes during frequency transitions but, IMHO,
it can be acceptable in many use cases.

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

Signed-off-by: Bastien Curutchet <[email protected]>
---
Change log v1 -> v2:
* Add details in commit log
* Drop alphabetic order in #include
* Drop a useless check in notifier callback

v1 : https://lore.kernel.org/all/[email protected]/
drivers/tty/serial/8250/8250_of.c | 37 +++++++++++++++++++++++++++++++
1 file changed, 37 insertions(+)

diff --git a/drivers/tty/serial/8250/8250_of.c b/drivers/tty/serial/8250/8250_of.c
index 5d1dd992d8fb..e14f47ef1172 100644
--- a/drivers/tty/serial/8250/8250_of.c
+++ b/drivers/tty/serial/8250/8250_of.c
@@ -18,6 +18,7 @@
#include <linux/pm_runtime.h>
#include <linux/clk.h>
#include <linux/reset.h>
+#include <linux/notifier.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 +60,26 @@ 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 (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 +240,19 @@ 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 +268,9 @@ 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

2024-04-05 12:48:25

by Herve Codina

Subject: Re: [PATCH v2 1/1] serial: 8250_of: Add clock_notifier

Hi Bastien,

On Fri, 5 Apr 2024 14:05:52 +0200
Bastien Curutchet <[email protected]> wrote:

> 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. Not using PRE_RATE_CHANGE notification can
> result in a few corrupted bytes during frequency transitions but, IMHO,
> it can be acceptable in many use cases.
>
> It has been tested on a DAVINCI/OMAP-L138 processor.
>
> Signed-off-by: Bastien Curutchet <[email protected]>

Reviewed-by: Herve Codina <[email protected]>

Best regards,
Hervé