On 10/12/2014 17:34, Paolo Bonzini wrote: > This is responsible for failure of migration from 2.2 to 2.1, because > thr_ipending is always one in practice. Calling serial_update_irq is > the right thing to do indeed, because writing to IER could cause an > interrupt to appear. However, there is no reason to set thr_ipending > again. > > This was already reported in 2010. See this quote from > https://lists.gnu.org/archive/html/qemu-devel/2010-03/msg01914.html: > >> The commit in r1049 (serial interrupt fix (Hampa Hug)) prevents >> booting Digital Research DOSPlus. Following patch partially reverts >> that commit and makes DOSPlus booting in QEMU again. > > Bochs does not check LSR_THRE in IER, and the log message in r1049 doesn't > explain why the change was made in the first place. > > This does not change the migration format, so 2.2.0 -> 2.1 will remain > broken but we can fix 2.2.1 -> 2.1 without breaking 2.2.1 <-> 2.2.0. > > Signed-off-by: Paolo Bonzini <pbonz...@redhat.com> > --- > hw/char/serial.c | 5 +---- > 1 file changed, 1 insertion(+), 4 deletions(-) > > diff --git a/hw/char/serial.c b/hw/char/serial.c > index ebcacdc..cf8e4e3 100644 > --- a/hw/char/serial.c > +++ b/hw/char/serial.c > @@ -350,10 +350,7 @@ static void serial_ioport_write(void *opaque, hwaddr > addr, uint64_t val, > s->poll_msl = 0; > } > } > - if (s->lsr & UART_LSR_THRE) { > - s->thr_ipending = 1; > - serial_update_irq(s); > - } > + serial_update_irq(s); > } > break; > case 2: >
Nope, this breaks the Windows UART driver. Paolo
