Re: [PATCH] serial: Two branches the same in timbuart_set_mctrl()

Re: [PATCH] serial: Two branches the same in timbuart_set_mctrl()

[Richard Röjfors]

Hi Roel,

On 01/17/2010 08:02 PM, Roel Kluin wrote:
> Dear Richard Röjfors,
>
> It is possible that I found a bug in the Timberdale UART driver that was added
> to the linux kernel. The patch below tries to fix this, note the RTS to CTS
> change, could you confirm whether the patch below changes your driver
> correctly?

Thanks for finding this, I have a comment on the patch below.

>
> Thank you,
>
> Roel Kluin
> ----------------->8----------------------------8<-------------------------------
> Regardless of whether the TIOCM_RTS bit was set in mctrl, the same write
> occurred.
>
> Signed-off-by: Roel Kluin<roel.kluin@gmail.com>
> ---
>   drivers/serial/timbuart.c |    2 +-
>   1 files changed, 1 insertions(+), 1 deletions(-)
>
> diff --git a/drivers/serial/timbuart.c b/drivers/serial/timbuart.c
> index 34b31da..c433d40 100644
> --- a/drivers/serial/timbuart.c
> +++ b/drivers/serial/timbuart.c
> @@ -219,7 +219,7 @@ static void timbuart_set_mctrl(struct uart_port *port, unsigned int mctrl)
>   	if (mctrl&  TIOCM_RTS)
>   		iowrite8(TIMBUART_CTRL_RTS, port->membase + TIMBUART_CTRL);
>   	else
> -		iowrite8(TIMBUART_CTRL_RTS, port->membase + TIMBUART_CTRL);
> +		iowrite8(TIMBUART_CTRL_CTS, port->membase + TIMBUART_CTRL);

This is not completely correct. CTS is a read only bit and we are to stop signal RTS.
So the line should look like:
iowrite8(0, port->membase + TIMBUART_CTRL);


>   }
>
>   static void timbuart_mctrl_check(struct uart_port *port, u32 isr, u32 *ier)

--Richard
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Re: [PATCH] serial: Two branches the same in timbuart_set_mctrl()

[Roel Kluin]

Hi Richard, 

>>       if (mctrl&  TIOCM_RTS)
>>           iowrite8(TIMBUART_CTRL_RTS, port->membase + TIMBUART_CTRL);
>>       else
>> -        iowrite8(TIMBUART_CTRL_RTS, port->membase + TIMBUART_CTRL);
>> +        iowrite8(TIMBUART_CTRL_CTS, port->membase + TIMBUART_CTRL);
> 
> This is not completely correct. CTS is a read only bit and we are to
> stop signal RTS. So the line should look like:
> iowrite8(0, port->membase + TIMBUART_CTRL);

It appears as if this will also unset TIMBUART_CTRL_CTS (which is
probably ok since it's read-only) but TIMBUART_CTRL_FLSHTX and
TIMBUART_CTRL_FLSHRX as well. If undesired we need something like this:

iowrite8(ioread8(port->membase + TIMBUART_CTRL) & ~TIMBUART_CTRL_RTS,
	port->membase + TIMBUART_CTRL);

If not required I'll send the patch as you suggested.

Regards, Roel

Re: [PATCH] serial: Two branches the same in timbuart_set_mctrl()

[Richard Röjfors]

On 03/15/2010 02:33 PM, Roel Kluin wrote:
> Hi Richard,
>
>>>        if (mctrl&   TIOCM_RTS)
>>>            iowrite8(TIMBUART_CTRL_RTS, port->membase + TIMBUART_CTRL);
>>>        else
>>> -        iowrite8(TIMBUART_CTRL_RTS, port->membase + TIMBUART_CTRL);
>>> +        iowrite8(TIMBUART_CTRL_CTS, port->membase + TIMBUART_CTRL);
>>
>> This is not completely correct. CTS is a read only bit and we are to
>> stop signal RTS. So the line should look like:
>> iowrite8(0, port->membase + TIMBUART_CTRL);
>
> It appears as if this will also unset TIMBUART_CTRL_CTS (which is
> probably ok since it's read-only) but TIMBUART_CTRL_FLSHTX and
> TIMBUART_CTRL_FLSHRX as well.

TIMBUART_CTRL_FLSH(RX/TX) are write only bits, writing a 1 to these will
flush the corresponding FIFO. In this case we should not flush the FIFO:s,
so writing 0 as I suggested is correct.

>
> If not required I'll send the patch as you suggested.

Great! Thanks!

--Richard

Re: [PATCH] serial: Two branches the same in timbuart_set_mctrl()

[Roel Kluin]

CTS is a read only bit and we are to stop signal RTS if modem line
TIOCM_RTS is not set.

Thanks for suggestions by Richard Röjfors.

Acked-by: Richard Röjfors <richard.rojfors@pelagicore.com>
Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
---
diff --git a/drivers/serial/timbuart.c b/drivers/serial/timbuart.c
index 7bf1026..823b9c5 100644
--- a/drivers/serial/timbuart.c
+++ b/drivers/serial/timbuart.c
@@ -219,7 +219,7 @@ static void timbuart_set_mctrl(struct uart_port *port, unsigned int mctrl)
 	if (mctrl & TIOCM_RTS)
 		iowrite8(TIMBUART_CTRL_RTS, port->membase + TIMBUART_CTRL);
 	else
-		iowrite8(TIMBUART_CTRL_RTS, port->membase + TIMBUART_CTRL);
+		iowrite8(0, port->membase + TIMBUART_CTRL);
 }
 
 static void timbuart_mctrl_check(struct uart_port *port, u32 isr, u32 *ier)
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