[alsa-devel] Driver code with mpc5200 pointer problem.

[Takashi Iwai]

At Tue, 28 Apr 2009 14:02:01 +0200,
I wrote:
> 
> At Tue, 28 Apr 2009 13:30:09 +0200 (CEST),
> Jaroslav Kysela wrote:
> > 
> > On Tue, 28 Apr 2009, Takashi Iwai wrote:
> > 
> > > At Tue, 28 Apr 2009 12:15:25 +0200 (CEST),
> > > Jaroslav Kysela wrote:
> > >>
> > >> On Tue, 28 Apr 2009, Takashi Iwai wrote:
> > >>
> > >>> Well, I think it'd be better, at this moment for 2.6.30, to allow
> > >>> problematic drivers to skip the jiffies check.  Adding the fundamental
> > >>> change at this late stage is bad, especially if the change wasn't
> > >>> tested much by many others and has an influence on user-side API.
> > >>>
> > >>> So, as I proposed, we can simply add the pcm info check, and add
> > >>> BATCH flag to needed drivers.  Of course, it still requires some
> > >>> more testing, but basically it'll take back to the old behavior and
> > >>> should be safer.
> > >>>
> > >>> Meanwhile, applying the delay account patch now for 2.6.31 should be
> > >>> good (ealier is better).  It doesn't conflict with the info flag
> > >>> check, so we can work parallel.
> > >>
> > >> Could we just add the runtime->delay variable without touching other code
> > >> (pcm status), to correct the jiffies based check now?
> > >
> > > That's possible, of course.
> > >
> > >> It seems like a good
> > >> step forward to me and the lowlevel drivers will be more prepared for next
> > >> PCM midlevel code changes.
> > >
> > > Well, but I guess providing the proper FIFO size isn't trivial to each
> > > driver.  There are many devices, as Mark suggested, which may be
> > > broken right now, and we can't determine all h/w specs and test them.
> > >
> > > OTOH, adding INFO_BATCH is fairly easy, because it can be found from
> > > the pointer callback implementation of each driver.  On these devices,
> > > the jiffies check doesn't help much anyway because it cannot update
> > > the hwptr any other than the period size.  So, skipping jiffies check
> > > is logically correct as a regression fix.
> > 
> > I don't see much difference between adding INFO_BATCH and adding 
> > runtime->delay = (runtime->period_size)-1 to avoid jiffies check for one 
> > period to these drivers (with some notice to author of the driver to 
> > correct this value).
> 
> INFO_BATCH is the correct flag for such drivers.  They should have the
> flag, independent from the fix.

So fixed now on sound git tree.  The drivers that can't report precise
position have now INFO_BATCH flag.

The workaround for jiffies check isn't applied yet.  Just this flags,
so far.


Takashi