ALSA: usb-audio: Expose sample resolution through proc interface

At least some USB devices use (MSB-aligned) audio format larger
than the actual resolution of the device. In order to expose the
actual device resolution (bBitResolution), add extra field to the
procfs stream info interface.
Signed-off-by: Jussi Laako <jussi@sonarnerd.net>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/usb/card.h

@@ -14,6 +14,7 @@ struct audioformat {
 	u64 formats;			/* ALSA format bits */
 	unsigned int channels;		/* # channels */
 	unsigned int fmt_type;		/* USB audio format type (1-3) */
+	unsigned int fmt_bits;		/* number of significant bits */
 	unsigned int frame_size;	/* samples per frame for non-audio */
 	int iface;			/* interface number */
 	unsigned char altsetting;	/* corresponding alternate setting */

sound/usb/format.c

@@ -87,6 +87,8 @@ static u64 parse_audio_format_i_type(struct snd_usb_audio *chip,
 	}
 	}
 
+	fp->fmt_bits = sample_width;
+
 	if ((pcm_formats == 0) &&
 	    (format == 0 || format == (1 << UAC_FORMAT_TYPE_I_UNDEFINED))) {
 		/* some devices don't define this correctly... */

sound/usb/proc.c

@@ -109,6 +109,7 @@ static void proc_dump_substream_formats(struct snd_usb_substream *subs, struct s
 		if (subs->speed != USB_SPEED_FULL)
 			snd_iprintf(buffer, "    Data packet interval: %d us\n",
 				    125 * (1 << fp->datainterval));
+		snd_iprintf(buffer, "    Bits: %d\n", fp->fmt_bits);
 		// snd_iprintf(buffer, "    Max Packet Size = %d\n", fp->maxpacksize);
 		// snd_iprintf(buffer, "    EP Attribute = %#x\n", fp->attributes);
 	}