[alsa-devel] [PATCH 7/7] ALSA: hda - Reduce verbs during generic parser initialization

[Takashi Iwai]

At Sat, 28 Feb 2015 10:51:29 +0100,
Lars-Peter Clausen wrote:
> 
> On 02/27/2015 10:28 PM, Takashi Iwai wrote:
> > For reducing the number of verbs performed during the initialization
> > and the resume of the generic parser, this patch (re-)introduces the
> > mechanism to cache everything in init and sync later.
> >
> > However, it became a bit tricky in the end: we can't use regcache's
> > cache_only flag straightforwardly here because we do want the actual
> > hardware access for reads if needed, but forbids only the writes.
> > So, instead, the regmap reg_write callback checks the own flag
> > (reusing the existing codec->cached_write) and skips the actual
> > access.  This works by assumption of regmap dumping the whole
> > registers via regcache_sync() at a later point.
> >
> > Signed-off-by: Takashi Iwai <tiwai at suse.de>
> > ---
> >   sound/pci/hda/hda_generic.c | 4 ++++
> >   sound/pci/hda/hda_regmap.c  | 6 ++++++
> >   2 files changed, 10 insertions(+)
> >
> > diff --git a/sound/pci/hda/hda_generic.c b/sound/pci/hda/hda_generic.c
> > index 33de31c83d6e..bcaed93f8795 100644
> > --- a/sound/pci/hda/hda_generic.c
> > +++ b/sound/pci/hda/hda_generic.c
> > @@ -5411,6 +5411,8 @@ int snd_hda_gen_init(struct hda_codec *codec)
> >
> >   	snd_hda_apply_verbs(codec);
> >
> > +	codec->cached_write = 1;
> > +
> 
> How about using regcache_cache_only(), this handles this internally in 
> regmap and will also make sure that the cache gets marked as dirty so that a 
> regcache_sync() will properly write out the dirty registers.

I tried this as a first option, too, but it doesn't work because we
still want reading the value from hardware if not read beforehand.
regcache_cache_only() prevents also from reading a h/w value.  It's
the point I mentioned this being tricky.


thanks,

Takashi