Re: [PATCH] pl011: assert RTS signal in case the receiver uses flow control

[Andre Przywara <andre.przywara@linaro.org>]

On 09/02/2013 05:53 PM, Julien Grall wrote:
> On 09/02/2013 03:51 PM, Andre Przywara wrote:
>> Although we do not support hardware flow control in the Xen driver
>> for the PL011 UART, the other end may be configured to use it.
>> In this case it waits in vain for the RTS signal to be asserted by
>> the host and will never transmit any characters.
>> This fixes the UART input on Calxeda Midway, which uses hardware
>> flow control for the serial-over-LAN functionality.
>>
>> Signed-off-by: Andre Przywara <andre.przywara@linaro.org>
>> ---
>>   xen/drivers/char/pl011.c         | 4 ++--
>>   xen/include/asm-arm/pl011-uart.h | 4 ++++
>>   2 files changed, 6 insertions(+), 2 deletions(-)
>>
>> diff --git a/xen/drivers/char/pl011.c b/xen/drivers/char/pl011.c
>> index 3ec6e10..e340961 100644
>> --- a/xen/drivers/char/pl011.c
>> +++ b/xen/drivers/char/pl011.c
>> @@ -120,8 +120,8 @@ static void __init pl011_init_preirq(struct serial_port *port)
>>       pl011_write(uart, IMSC, 0);
>>       pl011_write(uart, ICR, ALLI);
>>
>> -    /* Enable the UART for RX and TX; no flow ctrl */
>> -    pl011_write(uart, CR, RXE | TXE | UARTEN);
>> +    /* Enable the UART for RX and TX; assert RTS in case the other end cares */
>> +    pl011_write(uart, CR, RTS | RXE | TXE | UARTEN);
>>   }
>
> Instead of overriding CR can we read CR and enable the necessary bit?
> It seems that Linux doesn't set RTS but keep the level from the previous
> register value.

Right, that is the way to do it. In fact u-boot already cares about 
this: 
http://git.denx.de/?p=u-boot.git;a=commit;h=10501df05e2d2eef501c92483c134d5f7c9da150

Will send a new version.

> BTW, this patch works on the versatile express :).

Nice, thanks for testing.

Andre.