Re: [PATCH 1/2] ALSA: pcm: reinvent the stream synchronization ID API

[Jaroslav Kysela <perex@xxxxxxxx>]

On 07. 05. 24 5:04, Takashi Sakamoto wrote:

> > +/**
> > + * is sync id (clock id) empty?
> > + */
> > +static inline bool pcm_sync_empty(const unsigned char *sync)
> > +{
> > +	return strnlen((const char *)sync, 16) == 0;
> > +}
> > +
>
> For the sound card indexed by 0, it is problematic, since in the later
> change, the first element of array has 0.

Oops. It was a thinko. I replaced this with a full zero comparison in v3 of 
this patch.

...

> > @@ -420,7 +414,8 @@ struct snd_pcm_hw_params {
> >   	unsigned int rate_num;		/* R: rate numerator */
> >   	unsigned int rate_den;		/* R: rate denominator */
> >   	snd_pcm_uframes_t fifo_size;	/* R: chip FIFO size in frames */
> > -	unsigned char reserved[64];	/* reserved for future */
> > +	unsigned char sync[16];		/* R: synchronization ID (perfect sync - one clock source) */
> > +	unsigned char reserved[48];	/* reserved for future */
> >   };
> >   
> >   enum {
>
> As long as I checked, the above change are safe for
> backward-compatibility and compat ioctl. They keep the same size of
> structure and the same offset of member in each of i386/ILP32/LP64 data
> models,

Thank you for this verification and review.

> > +	*(__u32 *)runtime->sync = cpu_to_le32(substream->pcm->card->number);
> > +	memset(runtime->sync + 4, 0, sizeof(runtime->sync) - 4);
> > +	strncpy(runtime->sync + 4, "P16V", 4);
>    
> The serialization would not keep the same data before the change, since
> the third, fourth, and fifth elements are 0x31, 0x36, and 0x56, instead
> of 0x10, 0x56, and 0x00.

It does not matter. See the extended comment for snd_pcm_set_sync_per_card in 
v3. The ID should be used only for a comparison among PCM devices without any 
interpretation.

				Thank you,
					Jaroslav

--
Jaroslav Kysela <perex@xxxxxxxx>
Linux Sound Maintainer; ALSA Project; Red Hat, Inc.