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

[Tim Deegan <tim@xxxxxxx>]

At 16:51 +0200 on 02 Sep (1378140705), 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@xxxxxxxxxx>
> ---
>  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);
>  }
>  
>  static void __init pl011_init_postirq(struct serial_port *port)
> diff --git a/xen/include/asm-arm/pl011-uart.h 
> b/xen/include/asm-arm/pl011-uart.h
> index 3332c51..123f477 100644
> --- a/xen/include/asm-arm/pl011-uart.h
> +++ b/xen/include/asm-arm/pl011-uart.h
> @@ -38,6 +38,10 @@
>  #define DMACR  (0x48)
>  
>  /* CR bits */
> +#define CTSEN  (1<<15) /* automatic CTS hardware flow control */
> +#define RTSEN  (1<<14) /* automatic RTS hardware flow control */

Would this bit not be better than blindly setting RTS?

Tim.

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