[PATCH RFC] serial: mxs-auart: fix baud rate range

Currently mxs-auart doesn't care correctly about the baud rate divisor.
According to reference manual the baud rate divisor must be between
0x000000EC and 0x003FFFC0. So calculate the possible baud rate range
and use it for uart_get_baud_rate().

Signed-off-by: Stefan Wahren <redacted>
---
 drivers/tty/serial/mxs-auart.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

Here is a userspace application to test the new baud rate range:

https://gist.github.com/lategoodbye/f2d76134aa6c404cd92c

diff --git a/drivers/tty/serial/mxs-auart.c b/drivers/tty/serial/mxs-auart.c
index 13cf773..afe617c 100644
--- a/drivers/tty/serial/mxs-auart.c
+++ b/drivers/tty/serial/mxs-auart.c

@@ -659,7 +659,7 @@ static void mxs_auart_settermios(struct uart_port *u,
 {
 	struct mxs_auart_port *s = to_auart_port(u);
 	u32 bm, ctrl, ctrl2, div;
-	unsigned int cflag, baud;
+	unsigned int cflag, baud, baud_min, baud_max;
 
 	cflag = termios->c_cflag;
 

@@ -752,7 +752,9 @@ static void mxs_auart_settermios(struct uart_port *u,
 	}
 
 	/* set baud rate */
-	baud = uart_get_baud_rate(u, termios, old, 0, u->uartclk);
+	baud_min = u->uartclk * 32 / 0x3fffc0;
+	baud_max = u->uartclk * 32 / 0xec;
+	baud = uart_get_baud_rate(u, termios, old, baud_min, baud_max);
 	div = u->uartclk * 32 / baud;
 	ctrl |= AUART_LINECTRL_BAUD_DIVFRAC(div & 0x3F);
 	ctrl |= AUART_LINECTRL_BAUD_DIVINT(div >> 6);

-- 
1.7.9.5

On Mon, Aug 10, 2015 at 9:12 AM, Stefan Wahren [off-list ref] wrote:

        /* set baud rate */
-       baud = uart_get_baud_rate(u, termios, old, 0, u->uartclk);
+       baud_min = u->uartclk * 32 / 0x3fffc0;
+       baud_max = u->uartclk * 32 / 0xec;
+       baud = uart_get_baud_rate(u, termios, old, baud_min, baud_max);

Looks good. It would be nice to replace 0x3fffc0 and 0xec with defines though.

Regards,

Fabio Estevam

W dniu 2015-08-10 o 14:22, Fabio Estevam pisze:

On Mon, Aug 10, 2015 at 9:12 AM, Stefan Wahren [off-list ref] wrote:

quoted

         /* set baud rate */
-       baud = uart_get_baud_rate(u, termios, old, 0, u->uartclk);
+       baud_min = u->uartclk * 32 / 0x3fffc0;
+       baud_max = u->uartclk * 32 / 0xec;
+       baud = uart_get_baud_rate(u, termios, old, baud_min, baud_max);

Looks good. It would be nice to replace 0x3fffc0 and 0xec with defines though.

I agree with Fabio.

In addition let's look at the example for uartclk = 24MHz:
baud_max = 3,254,237.29 => will be rounded down to 3,254,237bauds and it 
is OK
baud_min = 183.1 => will be rounded to 183 bauds. To avoid div=0x400971 
it should be 184
so DIV_ROUND_UP() macro could be used.

best regards
Janusz

Regards,

Fabio Estevam

Hi Janusz,

Janusz Użycki [off-list ref] hat am 10. August 2015 um
19:01 geschrieben:




W dniu 2015-08-10 o 14:22, Fabio Estevam pisze:

quoted

On Mon, Aug 10, 2015 at 9:12 AM, Stefan Wahren [off-list ref]
wrote:

quoted

/* set baud rate */
- baud = uart_get_baud_rate(u, termios, old, 0, u->uartclk);
+ baud_min = u->uartclk * 32 / 0x3fffc0;
+ baud_max = u->uartclk * 32 / 0xec;
+ baud = uart_get_baud_rate(u, termios, old, baud_min, baud_max);

Looks good. It would be nice to replace 0x3fffc0 and 0xec with defines
though.

I agree with Fabio.

i will name them AUART_LINECTRL_BAUD_DIV_MIN and AUART_LINECTRL_BAUD_DIV_MAX.

In addition let's look at the example for uartclk = 24MHz:
baud_max = 3,254,237.29 => will be rounded down to 3,254,237bauds and it
is OK
baud_min = 183.1 => will be rounded to 183 bauds. To avoid div=0x400971
it should be 184
so DIV_ROUND_UP() macro could be used.

Thanks for pointing out. I will fix that.

Best regards
Stefan

best regards
Janusz

quoted

Regards,

Fabio Estevam

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