Re: [Qemu-devel] [PATCH 2/6] serial: reinstate watch after migration

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Paolo Bonzini (pbonzini@redhat.com) wrote:
> Otherwise, a serial port can get stuck if it is migrated while flow control
> is in effect.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  hw/char/serial.c         | 16 ++++++++++++++--
>  include/hw/char/serial.h |  1 +
>  2 files changed, 15 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/char/serial.c b/hw/char/serial.c
> index e65e9e0..6f0a49e 100644
> --- a/hw/char/serial.c
> +++ b/hw/char/serial.c
> @@ -639,8 +639,20 @@ static int serial_post_load(void *opaque, int version_id)
>      if (s->thr_ipending == -1) {
>          s->thr_ipending = ((s->iir & UART_IIR_ID) == UART_IIR_THRI);
>      }
> -    if (s->tsr_retry > MAX_XMIT_RETRY) {
> -        s->tsr_retry = MAX_XMIT_RETRY;

Why remove the check you just added?

> +
> +    if (s->tsr_retry > 0) {
> +        /* tsr_retry > 0 implies LSR.TEMT = 0 (transmitter not empty).  */
> +        if (s->lsr & UART_LSR_TEMT) {
> +            return -1;
> +        }
> +
> +        assert(s->watch_tag == 0);
> +        s->watch_tag = qemu_chr_fe_add_watch(s->chr, G_IO_OUT|G_IO_HUP, serial_xmit, s);
> +    } else {
> +        /* tsr_retry == 0 implies LSR.TEMT = 1 (transmitter empty).  */
> +        if (!(s->lsr & UART_LSR_TEMT)) {
> +            return -1;

If you're failing migration (-1) then please error_report to say why
so when someone hits it I can immediately see why.

Dave

> +        }
>      }
>  
>      s->last_break_enable = (s->lcr >> 6) & 1;
> diff --git a/include/hw/char/serial.h b/include/hw/char/serial.h
> index ef90615..2ab835c 100644
> --- a/include/hw/char/serial.h
> +++ b/include/hw/char/serial.h
> @@ -56,6 +56,7 @@ struct SerialState {
>      int it_shift;
>      int baudbase;
>      unsigned tsr_retry;
> +    unsigned watch_tag;
>      uint32_t wakeup;
>  
>      /* Time when the last byte was successfully sent out of the tsr */
> -- 
> 2.5.5
> 
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK