[alsa-devel] [PATCH] ASoC: Remove special casing for registerless widgets

Lu Guanqun guanqun.lu at intel.com
Sat Apr 2 10:22:00 CEST 2011

On Sat, Apr 02, 2011 at 04:18:02PM +0800, Mark Brown wrote:
> On Sat, Apr 02, 2011 at 04:12:44PM +0800, Lu Guanqun wrote:
> > On Sat, Apr 02, 2011 at 04:07:55PM +0800, Lu Guanqun wrote:
> > > But I still don't quite understand the write compression, it aims at
> > > reducing the number of register writes, however in
> > > dapm_seq_run_coalesced, it calls snd_soc_update_bits.
> > I mean, for write compression or not, as long as its widget register is
> > valid, it will be updated. So I don't see why write compression would
> > reduce the number...
> The idea is that since you often have all the enable bits together in a
> small set of registers if you're enabling two of the same widget type at
> once and they're both in the same register you can do it with one write.
> For example, if you're doing a stereo playback this will usually mean
> that enabling left and right DACs is one register write.  This is also
> good for pop/click performance as it ensures that both channels turn on
> simultaneously.

Thanks for the explaination. I get the idea.

> You can see this quite easily if you turn on DAPM pop debugging with a
> short delay - write to asoc/$CARD/dapm_pop_time in debugfs and start a
> playback or something and you'll see logging showing the writes being
> combined.

I'll try this and see the differences.

Thanks Mark!


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