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Commit 0dca01c3 authored by David Henningsson's avatar David Henningsson Committed by Takashi Iwai
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ALSA: usb: supply channel maps even when wChannelConfig is unspecified 



If wChannelconfig is given for some formats but not others, userspace
might not be able to set the channel map.

This is RFC because I'm not sure what the best behaviour is - to guess
the channel map from the given number of channels (it's quite likely
that one channel is MONO and two channels is FL FR), or just to supply
UNKNOWN for all channels.

But the complete lack of channel map for a format leads userspace to
believe that the format is not available at all. Or am I
misunderstanding how this should be used?

Signed-off-by: default avatarDavid Henningsson <david.henningsson@canonical.com>
Signed-off-by: default avatarTakashi Iwai <tiwai@suse.de>
parent 24eff328

sound/usb/stream.c

+13 −5
Original line number Diff line number Diff line
@@ -281,8 +281,6 @@ static struct snd_pcm_chmap_elem *convert_chmap(int channels, unsigned int bits, 
	const unsigned int *maps;

	int c;



	if (!bits)

		return NULL;

	if (channels > ARRAY_SIZE(chmap->map))

		return NULL;
@@ -293,9 +291,19 @@ static struct snd_pcm_chmap_elem *convert_chmap(int channels, unsigned int bits, 
	maps = protocol == UAC_VERSION_2 ? uac2_maps : uac1_maps;

	chmap->channels = channels;

	c = 0;

	for (; bits && *maps; maps++, bits >>= 1) {



	if (bits) {

		for (; bits && *maps; maps++, bits >>= 1)

			if (bits & 1)

				chmap->map[c++] = *maps;

	} else {

		/* If we're missing wChannelConfig, then guess something

		    to make sure the channel map is not skipped entirely */

		if (channels == 1)

			chmap->map[c++] = SNDRV_CHMAP_MONO;

		else

			for (; c < channels && *maps; maps++)

				chmap->map[c++] = *maps;

	}



	for (; c < channels; c++)