[alsa-devel] Problems with safe API and snd-cs46xx

[Takashi Iwai]

At Tue, 8 Sep 2009 09:19:33 +0100,
Sophie Hamilton wrote:
> 
> On 9/8/09, Takashi Iwai <tiwai at suse.de> wrote:
> > At Mon, 7 Sep 2009 20:06:37 +0100,
> >
> > Sophie Hamilton wrote:
> >  >
> >  > On 9/7/09, Takashi Iwai <tiwai at suse.de> wrote:
> >  > > At Mon, 7 Sep 2009 18:04:12 +0100,
> >  > > Sophie Hamilton wrote:
> >  > >  > Turns out that a value of 64 is the optimum value.
> >  > >
> >  > > How did you determine it ? :)
> >  >
> >  > Well, I have the actual hardware - at least, one of the chips it
> >  > supports - which is how I got involved in this bug in the first place.
> >  > (The Turtle Beach Santa Cruz uses a CS4630.) A value of 32 didn't work
> >  > when the default period side from ALSA is used; the next highest power
> >  > of two, 64, does.  As all the values I've seen in the kernel for the
> >  > minimum period size are powers of two, I'm assuming that this is the
> >  > lowest it can be. (I don't know much about ALSA, bear in mind; this is
> >  > my first venture into ALSA programming *and* kernel patches.)
> >
> > I asked it just because your description alone wasn't convincing
> >  enough.  That is, "it just works good for me" is no good explanation.
> >  The test was done on a single machine with a single application.
> >  It's possible that it would work on a monster 8GHz machine with
> >  another soundcard with a cs46xx chip with another application.
> 
> I take your point. However, if this was changed to 32, you'd
> presumably also need to change the default period/buffer size used by
> ALSA, as otherwise it would seem to be too low; my system doesn't like
> it. I'd suggest defaulting to 64, and then if any program has a
> specific latency need, they can test for underruns with different
> period sizes and find the best one.

Yeah, I know.  I raised it just as a hypothetical issue.  As I already
wrote, I'd take your fix as is.  A missing thing was a proper
explanation to convince others ;)

> >  However, as already mentioned, I find changing the value to 64 is
> >  somehow rational.  But, it's still a question whether this is the only
> >  fix...
> 
> Sadly, I don't know the answer to this one. But if there's anything I
> can do to help, let me know.
> 
> >  > >  > This should be the final patch. How should I go about submitting this?
> >  > >
> >  > > Please give a proper patch summary, too.
> >  > >  Also, it'd be more helpful if you give an example what actually
> >  > >  your patch fixes (e.g. audacious, etc).
> >  >
> >  > I'm not sure what you mean by a "proper patch summary". Is there
> >  > anywhere I should read that specifies the format of a proper patch
> >  > summary?
> >
> > A patch should have a single line summary to describe what it does.
> >  Take a look at $LINUX/Documentation/SubmittingPatches for details.
> 
> Okay. What I might do, given the instructions in the file, is send
> another email that conforms to all of the things in that file -
> subject line, CCs, etc. (for example, it says I should have CCed my
> patch to linux-kernel at vger.kernel.org too, and Linus ; obviously
> that'd have been a bad idea with the way my email was formatted now,
> but would it be a good idea to do those things now?)

Not necessary to send to LKML and Linus in this case.  It's a case
that can be solved solely in the subsystem tree, so it's enough to
send to the alsa-devel ML (and add me to Cc preferably).

> >  > As for what it fixes, it fixes a problem in the case where neither a
> >  > period size nor a buffer size is passed to ALSA, instead using the
> >  > defaults provided.
> [snipped long explanation]
> >  >
> >  > Does this help?
> >
> > Yes, but a bit more concisely if possible, please.
> >  The text will be recorded as a GIT changelog forever.  This is the
> >  best place where people see to track down the changes over tree.
> 
> Gotcha. How about:
> 
> "Fix minimum period size for cs46xx cards. This fixes a problem in the
> case where neither a period size nor a buffer size is passed to ALSA;
> this is the case in Audacious, OpenAL, and others."
> 
> Or is that *too* concise?

That's good enough.

I applied your patch now to sound git tree, so no need to resend.
It'll be included in the stable kernel tree later, too, once after
it's merged into Linus tree; this might be postponed until 2.6.32
merge window, though.


Thanks,

Takashi