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 <bastien.curutchet@xxxxxxxxxxx> --- 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/20240404074450.42708-1-bastien.curutchet@xxxxxxxxxxx/ 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
