Re: [RFC PATCH v2 1/2] serial: imx: Introduce timeout when waiting on transmitter empty

[Esben Haabendal <esben@geanix.com>]

Marc Kleine-Budde <mkl@pengutronix.de> writes:

> On 05.04.2024 09:56:37, Esben Haabendal wrote:
>> By waiting at most 1 second for USR2_TXDC to be set, we avoid a potentital
>> deadlock.
>>
>> In case of the timeout, there is not much we can do, so we simply ignore
>> the transmitter state and optimistically try to continue.
>> 
>> Signed-off-by: Esben Haabendal <esben@geanix.com>
>
> For the next round you should consult "scripts/get_maintainer.pl
> drivers/tty/serial/imx.c" and add these people/lists on Cc.

Yes. The idea was to do the RFC here on linux-rt, with focus on the 2nd
patch in the series. When that is in good shape, I will send the first
patch separately to all the proper maintainers and lists.

>> ---
>>  drivers/tty/serial/imx.c | 7 ++++---
>>  1 file changed, 4 insertions(+), 3 deletions(-)
>> 
>> diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
>> index 54b760d845c0..f7e4f38f08f3 100644
>> --- a/drivers/tty/serial/imx.c
>> +++ b/drivers/tty/serial/imx.c
>> @@ -26,6 +26,7 @@
>>  #include <linux/slab.h>
>>  #include <linux/of.h>
>>  #include <linux/io.h>
>> +#include <linux/iopoll.h>
>>  #include <linux/dma-mapping.h>
>>  
>>  #include <asm/irq.h>
>> @@ -1995,7 +1996,7 @@ imx_uart_console_write(struct console *co, const char *s, unsigned int count)
>>  	struct imx_port *sport = imx_uart_ports[co->index];
>>  	struct imx_port_ucrs old_ucr;
>>  	unsigned long flags;
>> -	unsigned int ucr1;
>> +	unsigned int ucr1, usr2;
>>  	int locked = 1;
>>  
>>  	if (sport->port.sysrq)
>> @@ -2026,8 +2027,8 @@ imx_uart_console_write(struct console *co, const char *s, unsigned int count)
>>  	 *	Finally, wait for transmitter to become empty
>>  	 *	and restore UCR1/2/3
>>  	 */
>> -	while (!(imx_uart_readl(sport, USR2) & USR2_TXDC));
>> -
>> +	read_poll_timeout_atomic(imx_uart_readl, usr2, usr2 & USR2_TXDC,
>> +				 0, 1000000, false, sport, USR2);
>
> You can make use of USEC_PER_SEC here.
>
> After fixing this, feel free to add my:
>
> Acked-by: Marc Kleine-Budde <mkl@pengutronix.de>

Thanks.

/Esben