[2/6] serial: reinstate watch after migration

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(-)

* 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

On 22/06/2016 17:05, Dr. David Alan Gilbert wrote:
> * 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?

Because I'm dumb. :)

>> +
>> +    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.

Ok, something like

    error_report("inconsistent state in serial device");

?

Paolo

* Paolo Bonzini (pbonzini@redhat.com) wrote:
> 
> 
> On 22/06/2016 17:05, Dr. David Alan Gilbert wrote:
> > * 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?
> 
> Because I'm dumb. :)
> 
> >> +
> >> +    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.
> 
> Ok, something like
> 
>     error_report("inconsistent state in serial device");
> 
> ?

Yeh, feel free to add tsr_retry and lsr to the message as well so that if you're
looking at it you can figure out what happened.

Dave

> 
> Paolo
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK