ALSA: usb-audio: Restrict rates for the shared clocks

When a single clock source is shared among several endpoints, we have
to keep the same rate on all active endpoints as long as the clock is
being used.  For dealing with such a case, this patch adds one more
check in the hw params constraint for the rate to take the shared
clocks into account.  The current rate is evaluated from the endpoint
list that applies the same clock source.

BugLink: https://bugzilla.suse.com/show_bug.cgi?id=1190418
Link: https://lore.kernel.org/r/20210929080844.11583-2-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/usb/card.h

@@ -136,6 +136,7 @@ struct snd_usb_endpoint {
 	unsigned int cur_period_frames;
 	unsigned int cur_period_bytes;
 	unsigned int cur_buffer_periods;
+	unsigned char cur_clock;
 
 	spinlock_t lock;
 	struct list_head list;

sound/usb/endpoint.c

@@ -722,6 +722,7 @@ snd_usb_endpoint_open(struct snd_usb_audio *chip,
 		ep->cur_period_frames = params_period_size(params);
 		ep->cur_period_bytes = ep->cur_period_frames * ep->cur_frame_bytes;
 		ep->cur_buffer_periods = params_periods(params);
+		ep->cur_clock = fp->clock;
 
 		if (ep->type == SND_USB_ENDPOINT_TYPE_SYNC)
 			endpoint_set_syncinterval(chip, ep);
@@ -833,6 +834,7 @@ void snd_usb_endpoint_close(struct snd_usb_audio *chip,
 		ep->altsetting = 0;
 		ep->cur_audiofmt = NULL;
 		ep->cur_rate = 0;
+		ep->cur_clock = 0;
 		ep->iface_ref = NULL;
 		usb_audio_dbg(chip, "EP 0x%x closed\n", ep->ep_num);
 	}
@@ -1340,6 +1342,25 @@ int snd_usb_endpoint_configure(struct snd_usb_audio *chip,
 	return err;
 }
 
+/* get the current rate set to the given clock by any endpoint */
+int snd_usb_endpoint_get_clock_rate(struct snd_usb_audio *chip, int clock)
+{
+	struct snd_usb_endpoint *ep;
+	int rate = 0;
+
+	if (!clock)
+		return 0;
+	mutex_lock(&chip->mutex);
+	list_for_each_entry(ep, &chip->ep_list, list) {
+		if (ep->cur_clock == clock && ep->cur_rate) {
+			rate = ep->cur_rate;
+			break;
+		}
+	}
+	mutex_unlock(&chip->mutex);
+	return rate;
+}
+
 /**
  * snd_usb_endpoint_start: start an snd_usb_endpoint
  *

sound/usb/endpoint.h

@@ -19,6 +19,7 @@ void snd_usb_endpoint_close(struct snd_usb_audio *chip,
 			    struct snd_usb_endpoint *ep);
 int snd_usb_endpoint_configure(struct snd_usb_audio *chip,
 			       struct snd_usb_endpoint *ep);
+int snd_usb_endpoint_get_clock_rate(struct snd_usb_audio *chip, int clock);
 
 bool snd_usb_endpoint_compatible(struct snd_usb_audio *chip,
 				 struct snd_usb_endpoint *ep,

sound/usb/pcm.c

@@ -734,6 +734,7 @@ static int hw_rule_rate(struct snd_pcm_hw_params *params,
 			struct snd_pcm_hw_rule *rule)
 {
 	struct snd_usb_substream *subs = rule->private;
+	struct snd_usb_audio *chip = subs->stream->chip;
 	const struct audioformat *fp;
 	struct snd_interval *it = hw_param_interval(params, SNDRV_PCM_HW_PARAM_RATE);
 	unsigned int rmin, rmax, r;
@@ -745,6 +746,14 @@ static int hw_rule_rate(struct snd_pcm_hw_params *params,
 	list_for_each_entry(fp, &subs->fmt_list, list) {
 		if (!hw_check_valid_format(subs, params, fp))
 			continue;
+		r = snd_usb_endpoint_get_clock_rate(chip, fp->clock);
+		if (r > 0) {
+			if (!snd_interval_test(it, r))
+				continue;
+			rmin = min(rmin, r);
+			rmax = max(rmax, r);
+			continue;
+		}
 		if (fp->rate_table && fp->nr_rates) {
 			for (i = 0; i < fp->nr_rates; i++) {
 				r = fp->rate_table[i];