Re: [PATCH] tty/serial: atmel: fix out of range clock divider handling

[David Engraf]

Hi,

On 13.12.19 at 10:57, Richard Genoud wrote:
> Hi,
>
> Le 11/12/2019 Ã 17:29, David Engraf a ÃcritÂ:
> > Use MCK_DIV8 when the clock divider is > 65535. Unfortunately the mode
> > register was already written thus the clock selection is ignored.
> >
> > Fix by writing the mode register after calculating the baudrate.
> >
> > Signed-off-by: David Engraf <david.engraf@xxxxxxxxx>
>
> It seems that this bug was introduced by:
> commit 5bf5635ac170 ("tty/serial: atmel: add fractional baud rate support")
>
> Could you add the "Fixes:" header ?

Sure.

> Ludovic, could you check if this was your intent at the time ?
>
> > ---
> >   drivers/tty/serial/atmel_serial.c | 6 +++---
> >   1 file changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/tty/serial/atmel_serial.c b/drivers/tty/serial/atmel_serial.c
> > index a8dc8af83f39..9983e2fabbac 100644
> > --- a/drivers/tty/serial/atmel_serial.c
> > +++ b/drivers/tty/serial/atmel_serial.c
> > @@ -2270,9 +2270,6 @@ static void atmel_set_termios(struct uart_port *port, struct ktermios *termios,
> >   		mode |= ATMEL_US_USMODE_NORMAL;
> >   	}
> >   
> I think it's better to mo move the "Set baud rate" block here (cf bellow)
>
> > -	/* set the mode, clock divisor, parity, stop bits and data size */
> > -	atmel_uart_writel(port, ATMEL_US_MR, mode);
> > -
> >   	/*
> >   	 * when switching the mode, set the RTS line state according to the
> >   	 * new mode, otherwise keep the former state
> > @@ -2315,6 +2312,9 @@ static void atmel_set_termios(struct uart_port *port, struct ktermios *termios,
> >   	}
> >   	quot = cd | fp << ATMEL_US_FP_OFFSET;
> >   
> > +	/* set the mode, clock divisor, parity, stop bits and data size */
> > +	atmel_uart_writel(port, ATMEL_US_MR, mode);
> > +
> I think your patch is good, but I'll be happier if instead of moving
> those 2 lines here, the whole "Set the baud rate" block was moved before
> "atmel_uart_writel(port, ATMEL_US_MR, mode);"
>
> That's because at line 2291 the ATMEL_US_CR register is set with
> ATMEL_US_RTSDIS or ATMEL_US_RTSEN.
> And those 2 values have a different effect depending on US_MR.USART_MODE
>
> Quoting from the relase manual:
> RTSEN:
> 1: Drives RTS pin to 1 if US_MR.USART_MODE field = 2, else drives RTS
> pin to 0 if US_MR.USART_MODE field = 0.
>
> RTSDIS:
> 1: Drives RTS pin to 0 if US_MR.USART_MODE field = 2, else drives RTS
> pin to 1 if US_MR.USART_MODE field = 0.
>
> So, I think it's better to set the mode register before setting the
> control register.

I fully agree, the RTS pin configuration depends on USART_MODE. I will 
make a new version of the patch.

Thanks
- David


> >   	if (!(port->iso7816.flags & SER_ISO7816_ENABLED))
> >   		atmel_uart_writel(port, ATMEL_US_BRGR, quot);
> >   	atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_RSTSTA | ATMEL_US_RSTRX);
>
> Thanks !