On Fri, Jul 26, 2013 at 12:05:33AM +0100, Russell King - ARM Linux wrote: > On Thu, Jul 25, 2013 at 08:19:05PM +0100, Mark Brown wrote: > > On Thu, Jul 25, 2013 at 11:14:59AM +0200, Jean-Francois Moine wrote:
> > > + if (np) {
> > > + priv->burst = 128; /* might be 32 or 128 */
> > > + } else if (data) {
> > When you posted this before I queried how and why the value might vary -
> > I see the code is the same and I don't recall a reply.
> This is the DMA burst size, and can be either 32 or 128 bytes according
> to the docs. Everyone seems to pass this as 128 bytes in their platform
> data to date, which I guess is why its ended up being hard coded as 128.
OK.
> However, whether it needs to be configurable or not is debatable - obviously
> the hardware allows it, but that doesn't mean it has to be exposed. If
> ALSA has some kind of way of specifying a "low latency" mode where 128
> byte vs 32 byte fetches would make a significant difference, then it may
> be something to look at.
This sort of configuration would normally be keyed off the period size
and so vary at runtime depending on what the application does when it
opens a stream. Sounds like something someone can worry about if they
have the requirement.
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