ALSA: usb-audio - Cache mixer values

Cache mixer values in usb-audio driver to reduce too excessive
accesses to the hardware.
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/usb/usbmixer.c

@@ -110,6 +110,8 @@ struct mixer_build {
 	const struct usbmix_selector_map *selector_map;
 };
 
+#define MAX_CHANNELS	10	/* max logical channels */
+
 struct usb_mixer_elem_info {
 	struct usb_mixer_interface *mixer;
 	struct usb_mixer_elem_info *next_id_elem; /* list of controls with same id */
@@ -120,6 +122,8 @@ struct usb_mixer_elem_info {
 	int channels;
 	int val_type;
 	int min, max, res;
+	int cached;
+	int cache_val[MAX_CHANNELS];
 	u8 initialized;
 };
 
@@ -181,8 +185,6 @@ enum {
 	USB_PROC_DCR_RELEASE = 6,
 };
 
-#define MAX_CHANNELS	10	/* max logical channels */
-
 
 /*
  * manual mapping of mixer names
@@ -376,11 +378,35 @@ static int get_cur_ctl_value(struct usb_mixer_elem_info *cval, int validx, int *
 }
 
 /* channel = 0: master, 1 = first channel */
-static inline int get_cur_mix_value(struct usb_mixer_elem_info *cval, int channel, int *value)
+static inline int get_cur_mix_raw(struct usb_mixer_elem_info *cval,
+				  int channel, int *value)
 {
 	return get_ctl_value(cval, GET_CUR, (cval->control << 8) | channel, value);
 }
 
+static int get_cur_mix_value(struct usb_mixer_elem_info *cval,
+			     int channel, int index, int *value)
+{
+	int err;
+
+	if (cval->cached & (1 << channel)) {
+		*value = cval->cache_val[index];
+		return 0;
+	}
+	err = get_cur_mix_raw(cval, channel, value);
+	if (err < 0) {
+		if (!cval->mixer->ignore_ctl_error)
+			snd_printd(KERN_ERR "cannot get current value for "
+				   "control %d ch %d: err = %d\n",
+				   cval->control, channel, err);
+		return err;
+	}
+	cval->cached |= 1 << channel;
+	cval->cache_val[index] = *value;
+	return 0;
+}
+
+
 /*
  * set a mixer value
  */
@@ -412,9 +438,17 @@ static int set_cur_ctl_value(struct usb_mixer_elem_info *cval, int validx, int v
 	return set_ctl_value(cval, SET_CUR, validx, value);
 }
 
-static inline int set_cur_mix_value(struct usb_mixer_elem_info *cval, int channel, int value)
+static int set_cur_mix_value(struct usb_mixer_elem_info *cval, int channel,
+			     int index, int value)
 {
-	return set_ctl_value(cval, SET_CUR, (cval->control << 8) | channel, value);
+	int err;
+	err = set_ctl_value(cval, SET_CUR, (cval->control << 8) | channel,
+			    value);
+	if (err < 0)
+		return err;
+	cval->cached |= 1 << channel;
+	cval->cache_val[index] = value;
+	return 0;
 }
 
 /*
@@ -718,7 +752,7 @@ static int get_min_max(struct usb_mixer_elem_info *cval, int default_min)
 		if (cval->min + cval->res < cval->max) {
 			int last_valid_res = cval->res;
 			int saved, test, check;
-			get_cur_mix_value(cval, minchn, &saved);
+			get_cur_mix_raw(cval, minchn, &saved);
 			for (;;) {
 				test = saved;
 				if (test < cval->max)
@@ -726,8 +760,8 @@ static int get_min_max(struct usb_mixer_elem_info *cval, int default_min)
 				else
 					test -= cval->res;
 				if (test < cval->min || test > cval->max ||
-				    set_cur_mix_value(cval, minchn, test) ||
-				    get_cur_mix_value(cval, minchn, &check)) {
+				    set_cur_mix_value(cval, minchn, 0, test) ||
+				    get_cur_mix_raw(cval, minchn, &check)) {
 					cval->res = last_valid_res;
 					break;
 				}
@@ -735,7 +769,7 @@ static int get_min_max(struct usb_mixer_elem_info *cval, int default_min)
 					break;
 				cval->res *= 2;
 			}
-			set_cur_mix_value(cval, minchn, saved);
+			set_cur_mix_value(cval, minchn, 0, saved);
 		}
 
 		cval->initialized = 1;
@@ -775,35 +809,25 @@ static int mixer_ctl_feature_get(struct snd_kcontrol *kcontrol, struct snd_ctl_e
 	struct usb_mixer_elem_info *cval = kcontrol->private_data;
 	int c, cnt, val, err;
 
+	ucontrol->value.integer.value[0] = cval->min;
 	if (cval->cmask) {
 		cnt = 0;
 		for (c = 0; c < MAX_CHANNELS; c++) {
-			if (cval->cmask & (1 << c)) {
-				err = get_cur_mix_value(cval, c + 1, &val);
-				if (err < 0) {
-					if (cval->mixer->ignore_ctl_error) {
-						ucontrol->value.integer.value[0] = cval->min;
-						return 0;
-					}
-					snd_printd(KERN_ERR "cannot get current value for control %d ch %d: err = %d\n", cval->control, c + 1, err);
-					return err;
-				}
+			if (!(cval->cmask & (1 << c)))
+				continue;
+			err = get_cur_mix_value(cval, c + 1, cnt, &val);
+			if (err < 0)
+				return cval->mixer->ignore_ctl_error ? 0 : err;
 			val = get_relative_value(cval, val);
 			ucontrol->value.integer.value[cnt] = val;
 			cnt++;
 		}
-		}
+		return 0;
 	} else {
 		/* master channel */
-		err = get_cur_mix_value(cval, 0, &val);
-		if (err < 0) {
-			if (cval->mixer->ignore_ctl_error) {
-				ucontrol->value.integer.value[0] = cval->min;
-				return 0;
-			}
-			snd_printd(KERN_ERR "cannot get current value for control %d master ch: err = %d\n", cval->control, err);
-			return err;
-		}
+		err = get_cur_mix_value(cval, 0, 0, &val);
+		if (err < 0)
+			return cval->mixer->ignore_ctl_error ? 0 : err;
 		val = get_relative_value(cval, val);
 		ucontrol->value.integer.value[0] = val;
 	}
@@ -820,34 +844,28 @@ static int mixer_ctl_feature_put(struct snd_kcontrol *kcontrol, struct snd_ctl_e
 	if (cval->cmask) {
 		cnt = 0;
 		for (c = 0; c < MAX_CHANNELS; c++) {
-			if (cval->cmask & (1 << c)) {
-				err = get_cur_mix_value(cval, c + 1, &oval);
-				if (err < 0) {
-					if (cval->mixer->ignore_ctl_error)
-						return 0;
-					return err;
-				}
+			if (!(cval->cmask & (1 << c)))
+				continue;
+			err = get_cur_mix_value(cval, c + 1, cnt, &oval);
+			if (err < 0)
+				return cval->mixer->ignore_ctl_error ? 0 : err;
 			val = ucontrol->value.integer.value[cnt];
 			val = get_abs_value(cval, val);
 			if (oval != val) {
-					set_cur_mix_value(cval, c + 1, val);
+				set_cur_mix_value(cval, c + 1, cnt, val);
 				changed = 1;
 			}
-				get_cur_mix_value(cval, c + 1, &val);
 			cnt++;
 		}
-		}
 	} else {
 		/* master channel */
-		err = get_cur_mix_value(cval, 0, &oval);
-		if (err < 0 && cval->mixer->ignore_ctl_error)
-			return 0;
+		err = get_cur_mix_value(cval, 0, 0, &oval);
 		if (err < 0)
-			return err;
+			return cval->mixer->ignore_ctl_error ? 0 : err;
 		val = ucontrol->value.integer.value[0];
 		val = get_abs_value(cval, val);
 		if (val != oval) {
-			set_cur_mix_value(cval, 0, val);
+			set_cur_mix_value(cval, 0, 0, val);
 			changed = 1;
 		}
 	}