Commit 157a57b6 authored by Daniel Mack's avatar Daniel Mack Committed by Takashi Iwai
Browse files

ALSA: usb-audio: move and add some comments 



Also add a list of open topics.

Signed-off-by: default avatarDaniel Mack <daniel@caiaq.de>
Signed-off-by: default avatarTakashi Iwai <tiwai@suse.de>
parent 21af7d8c

include/linux/usb/audio-v2.h

+15 −0
Original line number Diff line number Diff line
@@ -18,6 +18,21 @@ 
/* v1.0 and v2.0 of this standard have many things in common. For the rest

 * of the definitions, please refer to audio.h */



/*

 * bmControl field decoders

 *

 * From the USB Audio spec v2.0:

 *

 *   bmaControls() is a (ch+1)-element array of 4-byte bitmaps,

 *   each containing a set of bit pairs. If a Control is present,

 *   it must be Host readable. If a certain Control is not

 *   present then the bit pair must be set to 0b00.

 *   If a Control is present but read-only, the bit pair must be

 *   set to 0b01. If a Control is also Host programmable, the bit

 *   pair must be set to 0b11. The value 0b10 is not allowed.

 *

 */



static inline bool uac2_control_is_readable(u32 bmControls, u8 control)

{

	return (bmControls >> (control * 2)) & 0x1;

sound/usb/clock.c

+14 −2
Original line number Diff line number Diff line
@@ -120,8 +120,6 @@ static bool uac_clock_source_is_valid(struct snd_usb_audio *chip, int source_id) 
	return !!data;

}



/* Try to find the clock source ID of a given clock entity */



static int __uac_clock_find_source(struct snd_usb_audio *chip,

				   struct usb_host_interface *host_iface,

				   int entity_id, unsigned long *visited)
@@ -154,6 +152,8 @@ static int __uac_clock_find_source(struct snd_usb_audio *chip, 
		if (ret < 0)

			return ret;



		/* Selector values are one-based */



		if (ret > selector->bNrInPins || ret < 1) {

			printk(KERN_ERR

				"%s(): selector reported illegal value, id %d, ret %d\n",
@@ -176,6 +176,17 @@ static int __uac_clock_find_source(struct snd_usb_audio *chip, 
	return -EINVAL;

}



/*

 * For all kinds of sample rate settings and other device queries,

 * the clock source (end-leaf) must be used. However, clock selectors,

 * clock multipliers and sample rate converters may be specified as

 * clock source input to terminal. This functions walks the clock path

 * to its end and tries to find the source.

 *

 * The 'visited' bitfield is used internally to detect recursive loops.

 *

 * Returns the clock source UnitID (>=0) on success, or an error.

 */

int snd_usb_clock_find_source(struct snd_usb_audio *chip,

			      struct usb_host_interface *host_iface,

			      int entity_id)
@@ -246,6 +257,7 @@ static int set_sample_rate_v2(struct snd_usb_audio *chip, int iface, 
		return clock;



	if (!uac_clock_source_is_valid(chip, clock)) {

		/* TODO: should we try to find valid clock setups by ourself? */

		snd_printk(KERN_ERR "%d:%d:%d: clock source %d is not valid, cannot use\n",

			   dev->devnum, iface, fmt->altsetting, clock);

		return -ENXIO;

sound/usb/mixer.c

+16 −8
Original line number Diff line number Diff line
@@ -26,6 +26,22 @@ 
 *

 */



/*

 * TODOs, for both the mixer and the streaming interfaces:

 *

 *  - support for UAC2 effect units

 *  - support for graphical equalizers

 *  - RANGE and MEM set commands (UAC2)

 *  - RANGE and MEM interrupt dispatchers (UAC2)

 *  - audio channel clustering (UAC2)

 *  - audio sample rate converter units (UAC2)

 *  - proper handling of clock multipliers (UAC2)

 *  - dispatch clock change notifications (UAC2)

 *  	- stop PCM streams which use a clock that became invalid

 *  	- stop PCM streams which use a clock selector that has changed

 *  	- parse available sample rates again when clock sources changed

 */



#include <linux/bitops.h>

#include <linux/init.h>

#include <linux/list.h>
@@ -1199,14 +1215,6 @@ static int parse_audio_feature_unit(struct mixer_build *state, int unitid, void 
		}

	} else { /* UAC_VERSION_2 */

		for (i = 0; i < 30/2; i++) {

			/* From the USB Audio spec v2.0:

			   bmaControls() is a (ch+1)-element array of 4-byte bitmaps,

			   each containing a set of bit pairs. If a Control is present,

			   it must be Host readable. If a certain Control is not

			   present then the bit pair must be set to 0b00.

			   If a Control is present but read-only, the bit pair must be

			   set to 0b01. If a Control is also Host programmable, the bit

			   pair must be set to 0b11. The value 0b10 is not allowed. */

			unsigned int ch_bits = 0;

			unsigned int ch_read_only = 0;