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

[Takashi Iwai]

At Sat, 28 Feb 2015 11:27:42 +0100,
Lars-Peter Clausen wrote:
> 
> On 02/28/2015 11:01 AM, Takashi Iwai wrote:
> > 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.
> 
> Hm, right, I skipped right past that. But I think it will still be better to 
> implement this write-only caching in the regmap layer.

Yeah, that would make sense, I'm not against it :)


Takashi