Commit 24d2d3c5 authored by Geoffrey D. Bennett's avatar Geoffrey D. Bennett Committed by Takashi Iwai
Browse files

ALSA: usb-audio: Improve Focusrite sample rate filtering 



Replace the bLength == 10 max_rate check in
focusrite_valid_sample_rate() with filtering that also examines the
bmControls VAL_ALT_SETTINGS bit.

When VAL_ALT_SETTINGS is readable, the device uses strict
per-altsetting rate filtering (only the highest rate pair for that
altsetting is valid). When it is not readable, all rates up to
max_rate are valid.

For devices without the bLength == 10 Format Type descriptor extension
but with VAL_ALT_SETTINGS readable and multiple altsettings (only seen
in Scarlett 18i8 3rd Gen playback), fall back to the Focusrite
convention: alt 1 = 48kHz, alt 2 = 96kHz, alt 3 = 192kHz.

This produces correct rate tables for all tested Focusrite devices
(all Scarlett 2nd, 3rd, and 4th Gen, Clarett+, and Vocaster) using
only USB descriptors, allowing QUIRK_FLAG_VALIDATE_RATES to be removed
for Focusrite in the next commit.

Signed-off-by: default avatarGeoffrey D. Bennett <g@b4.vu>
Signed-off-by: default avatarTakashi Iwai <tiwai@suse.de>
Link: https://patch.msgid.link/7e18c1f393a6ecb6fc75dd867a2c4dbe135e3e22.1771594828.git.g@b4.vu
parent 9fb16a5c

sound/usb/format.c

+65 −5
Original line number Diff line number Diff line
@@ -305,17 +305,48 @@ static bool s1810c_valid_sample_rate(struct audioformat *fp, 
}



/*

 * Many Focusrite devices supports a limited set of sampling rates per

 * altsetting. Maximum rate is exposed in the last 4 bytes of Format Type

 * descriptor which has a non-standard bLength = 10.

 * Focusrite devices use rate pairs: 44100/48000, 88200/96000, and

 * 176400/192000. Return true if rate is in the pair for max_rate.

 */

static bool focusrite_rate_pair(unsigned int rate,

				unsigned int max_rate)

{

	switch (max_rate) {

	case 48000:  return rate == 44100 || rate == 48000;

	case 96000:  return rate == 88200 || rate == 96000;

	case 192000: return rate == 176400 || rate == 192000;

	default:     return true;

	}

}



/*

 * Focusrite devices report all supported rates in a single clock

 * source but only a subset is valid per altsetting.

 *

 * Detection uses two descriptor features:

 *

 * 1. Format Type descriptor bLength == 10: non-standard extension

 *    with max sample rate in bytes 6..9.

 *

 * 2. bmControls VAL_ALT_SETTINGS readable bit: when set, the device

 *    only supports the highest rate pair for that altsetting, and when

 *    clear, all rates up to max_rate are valid.

 *

 * For devices without the bLength == 10 extension but with

 * VAL_ALT_SETTINGS readable and multiple altsettings (only seen in

 * Scarlett 18i8 3rd Gen playback), fall back to the Focusrite

 * convention: alt 1 = 48kHz, alt 2 = 96kHz, alt 3 = 192kHz.

 */

static bool focusrite_valid_sample_rate(struct snd_usb_audio *chip,

					struct audioformat *fp,

					unsigned int rate)

{

	struct usb_interface *iface;

	struct usb_host_interface *alts;

	struct uac2_as_header_descriptor *as;

	unsigned char *fmt;

	unsigned int max_rate;

	bool val_alt;



	alts = snd_usb_get_host_interface(chip, fp->iface, fp->altsetting);

	if (!alts)
@@ -326,9 +357,21 @@ static bool focusrite_valid_sample_rate(struct snd_usb_audio *chip, 
	if (!fmt)

		return true;



	as = snd_usb_find_csint_desc(alts->extra, alts->extralen,

				     NULL, UAC_AS_GENERAL);

	if (!as)

		return true;



	val_alt = uac_v2v3_control_is_readable(as->bmControls,

					       UAC2_AS_VAL_ALT_SETTINGS);



	if (fmt[0] == 10) { /* bLength */

		max_rate = combine_quad(&fmt[6]);



		if (val_alt)

			return focusrite_rate_pair(rate, max_rate);



		/* No val_alt: rates fall through from higher */

		switch (max_rate) {

		case 192000:

			if (rate == 176400 || rate == 192000)
@@ -344,12 +387,29 @@ static bool focusrite_valid_sample_rate(struct snd_usb_audio *chip, 
			usb_audio_info(chip,

				"%u:%d : unexpected max rate: %u\n",

				fp->iface, fp->altsetting, max_rate);



			return true;

		}

	}



	if (!val_alt)

		return true;



	/* Multi-altsetting device with val_alt but no max_rate

	 * in the format descriptor. Use Focusrite convention:

	 * alt 1 = 48kHz, alt 2 = 96kHz, alt 3 = 192kHz.

	 */

	iface = usb_ifnum_to_if(chip->dev, fp->iface);

	if (!iface || iface->num_altsetting <= 2)

		return true;



	switch (fp->altsetting) {

	case 1:		max_rate = 48000; break;

	case 2:		max_rate = 96000; break;

	case 3:		max_rate = 192000; break;

	default:	return true;

	}



	return focusrite_rate_pair(rate, max_rate);

}



/*