[alsa-devel] Problems with safe API and snd-cs46xx
sophie-alsa at theblob.org
Tue Sep 8 10:19:33 CEST 2009
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.
> 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
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?)
> > 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?
Thanks for your comments,
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