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

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
......@@ -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;
......
......@@ -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;
......
......@@ -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;
......
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