Re: [Qemu-devel] [PATCH v3 for-2.11 3/3] tpm_tis: Return 0 for every register in case of failure mode

[Stefan Berger]

On 11/14/2017 06:47 PM, Marc-André Lureau wrote:
> Hi
>
> On Tue, Nov 14, 2017 at 10:52 PM, Stefan Berger
> <address@hidden> wrote:
> > Rather than returning ~0, return 0 for every register in case of
> > failure mode. The '0' is better to indicate that there's no device
> > there.
> For most registers, 0 makes more sense. However, I wonder if we
> shouldn't just fail to start qemu in this case...
>
> Not convincing me this is 2.11 material either. Does this fix a specific bug?

Yes, SeaBIOS detects the ~0 when it probes and thinks there's a device 
there. It then hangs trying to set flags and read registers to be able 
to use the device.

   Stefan

> > Signed-off-by: Stefan Berger <address@hidden>
> > ---
> >   hw/tpm/tpm_tis.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/hw/tpm/tpm_tis.c b/hw/tpm/tpm_tis.c
> > index fec2fc6..42d647d 100644
> > --- a/hw/tpm/tpm_tis.c
> > +++ b/hw/tpm/tpm_tis.c
> > @@ -545,7 +545,7 @@ static uint64_t tpm_tis_mmio_read(void *opaque, hwaddr addr,
> >       uint8_t v;
> >
> >       if (tpm_backend_had_startup_error(s->be_driver)) {
> > -        return val;
> > +        return 0;
> >       }
> >
> >       switch (offset) {
> > --
> > 2.5.5