ALSA: USB-audio: Adjust max packet size calculation for tx_length_quirk (759c90fe) · Commits · 戴 / test

For the Zoom R16/24 (tx_length_quirk set), when calculating the maximum sample frequency, consideration must be made for the fact that four bytes of the packet contain a length descriptor and consequently must not be counted as part of the audio data. This is corroborated by the wMaxPacketSize for this device, which is 108 bytes according for the USB playback endpoint descriptor. The frame size is 8 bytes (2 channels of 4 bytes each), and the 108 bytes thus work out as 13 * 8 + 4, i.e. corresponding to 13 frames plus the additional 4 byte length descriptor. Signed-off-by:

Ricard Wanderlof <ricardw@axis.com> Signed-off-by:

Takashi Iwai <tiwai@suse.de>

sound/usb/endpoint.c

+10 −2

Original line number	Diff line number	Diff line
		@@ -617,6 +617,8 @@ static int data_ep_set_params(struct snd_usb_endpoint *ep,
		unsigned int max_packs_per_period, urbs_per_period, urb_packs;
		unsigned int max_urbs, i;
		int frame_bits = snd_pcm_format_physical_width(pcm_format) * channels;
		int tx_length_quirk = (ep->chip->tx_length_quirk &&
		usb_pipeout(ep->pipe));

		if (pcm_format == SNDRV_PCM_FORMAT_DSD_U16_LE && fmt->dsd_dop) {
		/*
		@@ -650,11 +652,17 @@ static int data_ep_set_params(struct snd_usb_endpoint *ep,
		*/
		maxsize = (((ep->freqmax << ep->datainterval) + 0xffff) >> 16) *
		(frame_bits >> 3);
		if (tx_length_quirk)
		maxsize += sizeof(__le32); /* Space for length descriptor */
		/* but wMaxPacketSize might reduce this */
		if (ep->maxpacksize && ep->maxpacksize < maxsize) {
		/* whatever fits into a max. size packet */
		maxsize = ep->maxpacksize;
		ep->freqmax = (maxsize / (frame_bits >> 3))
		unsigned int data_maxsize = maxsize = ep->maxpacksize;

		if (tx_length_quirk)
		/* Need to remove the length descriptor to calc freq */
		data_maxsize -= sizeof(__le32);
		ep->freqmax = (data_maxsize / (frame_bits >> 3))
		<< (16 - ep->datainterval);
		}

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