At Wed, 21 Nov 2007 16:17:41 +0100, Clemens Ladisch wrote: > > Takashi Iwai wrote: > > Yes, querying channel mapping is another missing piece with popular > > demand. > > > > The implementation would be easy, I guess. But we have to define the > > way to inform this from kernel to user space: whether create a new > > ioctl or extend the existing ones (if possible)... > > It's just metadata that describes a PCM device, so I think we should use > TLV for this. Yes, TLV came to my mind, too. First I thought it might be possible to extend channel_info, but it's apparently not. So, an ioctl would be the only way. > The existing struct snd_ctl_tlv uses a single integer to identify > control elements. We could restrict control numid's to 31 bits and > use the upper bit to signal that this value includes device type and > device number in the lower bits, if we want to reuse the same TLV > ioctls. IMO, adding a new ioctl to PCM is better than reusing ctl TLV. The channel mapping is variable and depends on the hw_params currently set. So, it cannot be returned properly until a PCM is opened. Impelenting it in ctl ioctl implies rather a global information. Takashi _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
