[alsa-devel] [PATCH 1/3] ALSA: pcm: add IEC958 channel status update

[Takashi Iwai]

On Mon, 07 Dec 2015 09:46:02 +0100,
Moise Gergaud wrote:
> 
> On 12/03/2015 01:03 PM, Takashi Iwai wrote:
> > On Thu, 03 Dec 2015 12:13:04 +0100,
> > Russell King - ARM Linux wrote:
> >>
> >> On Thu, Dec 03, 2015 at 11:58:14AM +0100, Moise Gergaud wrote:
> >>> On 12/02/2015 08:00 PM, Russell King - ARM Linux wrote:
> >>>> Again, I'm not happy with this change.  The intention here is that we
> >>>> validate all arguments before we change anything.  This breaks that
> >>>> principle.
> >>>>
> >>> We propose this change for compressed mode (IEC61937/non linear PCM).
> >>> In case of compressed mode, iec958 channel status byte 0 bit1 = 1, then we
> >>> cannot use snd_pcm_create_iec958_consumer.
> >>
> >> Why can you not use snd_pcm_create_iec958_consumer() for this case?  You
> >> are allowed to modify the values you get afterwards in order to handle
> >> this case if you so wish to toggle this bit.
> >>
> >> However, if you are using data mode, you really should be using the AES
> >> bytes passed by the application through alsalib and into the kernel via
> >> the IEC958 controls.  There are three controls specified for this:
> >>
> >> SNDRV_CTL_NAME_IEC958("", PLAYBACK, CON_MASK) - the bits which can be
> >> changed for consumer mode.
> >> SNDRV_CTL_NAME_IEC958("", PLAYBACK, PRO_MASK) - the bits which can be
> >> changed for professional mode.
> >> SNDRV_CTL_NAME_IEC958("", PLAYBACK, DEFAULT) - the value of the changable
> >> bits.
> >>
> >> When using this, it is userspace's responsibility to set the sample rate
> >> appropriately for the stream.
> >>
> >> The only case to use snd_pcm_create_iec958_consumer() is to generate the
> >> status bytes for PCM audio, where the userspace API doesn't facilitiate
> >> generating and/or passing the AES status bytes.
> >
> > That's true.  OTOH, in most drivers, we try to be kind not to be too
> > strict for this requirement and adjust the status bits accordingly.
> > This comes from the lessons we learned how user-space doesn't care the
> > things.
> >
> > So, if we want to keep that good uncle attitude, this change doesn't
> > look so bad to me.
> >
> shall I deliver a new version of this patch with header correction or 
> shall I abandon this patch?

It's up to you whether you want further convincing Russell :)
I'd happily merge this once when we get his ack.


thanks,

Takashi