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.