Re: [PATCH 1/2] ALSA: firewire-tascam: Fix infinite loop in snd_tscm_stream_get_rate()

[Takashi Sakamoto]

On May 15 2017 23:22, Geert Uytterhoeven wrote:
> > > diff --git a/sound/firewire/tascam/tascam-stream.c
> > > b/sound/firewire/tascam/tascam-stream.c
> > > index f1657a4e0621ef49..e433b92ac6904db5 100644
> > > --- a/sound/firewire/tascam/tascam-stream.c
> > > +++ b/sound/firewire/tascam/tascam-stream.c
> > > @@ -84,7 +84,7 @@ int snd_tscm_stream_get_rate(struct snd_tscm *tscm,
> > > unsigned int *rate)
> > >         unsigned int trials = 0;
> > >         int err;
> > >
> > > -       while (data == 0x0 || trials++ < 5) {
> > > +       while (data == 0x0 && trials++ < 5) {
> > >                 err = get_clock(tscm, &data);
> > >                 if (err < 0)
> > >                         return err;
> >
> > Yep. It looks a bug.
> >
> > ...However, removal of the bug causes issue that the driver fails to start a
> > pair of capture/playback PCM substream when application requests them mostly
> > the same time, like jackd process.
> >
> > I think I did apply the bug as a makeshift workaround, then forgot itself
> > when developing the driver... I'd like to have a bit time for further
> > investigation, then post my fix in this development period.
>
> Probably you need a small delay in the loop?
> Why else do you #include <linux/delay.h>? ;-)

I know PDI1394L40 (link layer) has quirks inconvenient to us. 
Furthermore, the behaviour of on-board FPGAs with unique firmwares are 
in black boxes to me.

I prefer deliberate approach for this kind of work, reverse engineering.


Regards

Takashi Sakamoto