[alsa-devel] [PATCH v2 0/5] topology: Enhance support for private data

[Lin, Mengdong]

> -----Original Message-----
> From: alsa-devel-bounces at alsa-project.org
> [mailto:alsa-devel-bounces at alsa-project.org] On Behalf Of Vinod Koul
> Sent: Tuesday, July 19, 2016 12:00 PM
> To: Lin, Mengdong
> Cc: alsa-devel at alsa-project.org; Mengdong Lin; tiwai at suse.de; Takashi
> Sakamoto; broonie at kernel.org; Girdwood, Liam R; Nc, Shreyas
> Subject: Re: [alsa-devel] [PATCH v2 0/5] topology: Enhance support for
> private data
> 
> On Mon, Jul 18, 2016 at 03:06:24PM +0000, Lin, Mengdong wrote:
> >
> > > -----Original Message-----
> > > From: Takashi Sakamoto [mailto:o-takashi at sakamocchi.jp]
> > > Sent: Monday, July 18, 2016 11:43 AM
> >
> > > I know all of what you explained. Therefore, You misunderstand about
> > > my suggestion.
> > >
> > > What I suggested is to drop a support of
> SNDRV_CTL_ELEM_ACCESS_USER
> > > flag from current topology implementation in userspace library,
> > > because current implementation of ALSA SoC part doesn't support it.
> > >
> > > In ALSA SoC part, snd_ctl_new1() is called to add a control element
> > > set as a result of parsing binary blob generated by topology
> implementation.
> > >
> > > In snd_ctl_new1(), SNDRV_CTL_ELEM_ACCESS_USER flag is dropped, in
> > > these
> > > lines:
> > > http://git.kernel.org/cgit/linux/kernel/git/tiwai/sound.git/tree/sou
> > > nd/core/c
> > > ontrol.c#n263
> > >
> > > Totally, the flag cannot be supported by current implementation of
> > > topology in kernel. Thus, in userspace, we should drop this line to
> > > prevent users from
> > > confusions:
> > > http://git.alsa-project.org/?p=alsa-lib.git;a=blob;f=src/topology/ct
> > > l.c;h=b94
> > > 8ac021ceecc116bc1087075743243e4b14055;hb=HEAD#l44
> > >
> > > That's all what I mentioned. If something unclear, please tell it to me.
> >
> > Yes, you're right. snd_ctl_new1() dropped
> SNDRV_CTL_ELEM_ACCESS_USER flag.
> > I'll remove this from the topology user space tool to avoid confusion.
> 
> Oh no, that won't be a good idea.

Hi Vinod,

I think topology will drop support for only one flag "SNDRV_CTL_ELEM_ACCESS_USER". All other access flags are still supported.

Thanks
Mengdong

> 
> We would like to specify the access for controls from topology. Some controls
> can be read only and some write only :)
> 
> For example, any VU-meter controls should be read-only. Similarly if we have
> some user data being sent to some modules which can do do all fancy audio
> detection then these controls should be write-only.
> 
> Yes it seems to be broken by this, but we should fix it rather than remove.
> 
> --
> ~Vinod
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