usb: gadget: u_audio: Rate ctl notifies about current srate (0=stopped)

The Playback/Capture ctl currently reports rate value set by USB
control selector UAC2_CS_CONTROL_SAM_FREQ (fixed for UAC1). When the
stops playback/capture, the reported value does not change.  The gadget
side has no information whether the host has started/stopped
capture/playback.

This patch sets the value reported by the respective rate ctl to zero
when the host side has stopped playback/capture. Also, it calls
snd_ctl_notify when start/stop  occurs, so that a subscribed client can
act appropriately.

Tests have confirmed that USB hosts change UAC2_CS_CONTROL_SAM_FREQ
before switching altsetting to activate playback/capture, resulting in
correct order (params->c/p_srate is set to requested rate before
u_audio_start_capture/playback is called).

The gadget rate notifications are used by user-space audio gadget
controller gaudio_ctl https://github.com/pavhofman/gaudio_ctl.

Signed-off-by: Pavel Hofman <pavel.hofman@ivitera.com>
Link: https://lore.kernel.org/r/20220121155308.48794-8-pavel.hofman@ivitera.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/usb/gadget/function/u_audio.c b/drivers/usb/gadget/function/u_audio.c
index 283a449a953823ccd775dcdbe6f335e3017bad84..fab1bc43900200552ec651d75d809262c6452d17 100644 (file)
--- a/drivers/usb/gadget/function/u_audio.c
+++ b/drivers/usb/gadget/function/u_audio.c
@@ -65,6 +65,7 @@ struct uac_rtd_params {
 
        struct snd_kcontrol *snd_kctl_rate; /* read-only current rate */
        int srate; /* selected samplerate */
+       int active; /* playback/capture running */
 
   spinlock_t lock; /* lock for control transfers */
 
@@ -490,6 +491,21 @@ static inline void free_ep_fback(struct uac_rtd_params *prm, struct usb_ep *ep)
                dev_err(uac->card->dev, "%s:%d Error!\n", __func__, __LINE__);
 }
 
+static void set_active(struct uac_rtd_params *prm, bool active)
+{
+       // notifying through the Rate ctrl
+       struct snd_kcontrol *kctl = prm->snd_kctl_rate;
+       unsigned long flags;
+
+       spin_lock_irqsave(&prm->lock, flags);
+       if (prm->active != active) {
+               prm->active = active;
+               snd_ctl_notify(prm->uac->card, SNDRV_CTL_EVENT_MASK_VALUE,
+                               &kctl->id);
+       }
+       spin_unlock_irqrestore(&prm->lock, flags);
+}
+
 int u_audio_set_capture_srate(struct g_audio *audio_dev, int srate)
 {
        struct uac_params *params = &audio_dev->params;
@@ -607,6 +623,8 @@ int u_audio_start_capture(struct g_audio *audio_dev)
                        dev_err(dev, "%s:%d Error!\n", __func__, __LINE__);
        }
 
+       set_active(&uac->c_prm, true);
+
        ep_fback = audio_dev->in_ep_fback;
        if (!ep_fback)
                return 0;
@@ -652,6 +670,7 @@ void u_audio_stop_capture(struct g_audio *audio_dev)
 {
        struct snd_uac_chip *uac = audio_dev->uac;
 
+       set_active(&uac->c_prm, false);
        if (audio_dev->in_ep_fback)
                free_ep_fback(&uac->c_prm, audio_dev->in_ep_fback);
        free_ep(&uac->c_prm, audio_dev->out_ep);
@@ -723,6 +742,8 @@ int u_audio_start_playback(struct g_audio *audio_dev)
                        dev_err(dev, "%s:%d Error!\n", __func__, __LINE__);
        }
 
+       set_active(&uac->p_prm, true);
+
        return 0;
 }
 EXPORT_SYMBOL_GPL(u_audio_start_playback);
@@ -731,6 +752,7 @@ void u_audio_stop_playback(struct g_audio *audio_dev)
 {
        struct snd_uac_chip *uac = audio_dev->uac;
 
+       set_active(&uac->p_prm, false);
        free_ep(&uac->p_prm, audio_dev->in_ep);
 }
 EXPORT_SYMBOL_GPL(u_audio_stop_playback);
@@ -1074,7 +1096,11 @@ static int u_audio_rate_get(struct snd_kcontrol *kcontrol,
        unsigned long flags;
 
        spin_lock_irqsave(&prm->lock, flags);
-       ucontrol->value.integer.value[0] = prm->srate;
+       if (prm->active)
+               ucontrol->value.integer.value[0] = prm->srate;
+       else
+               /* not active: reporting zero rate */
+               ucontrol->value.integer.value[0] = 0;
        spin_unlock_irqrestore(&prm->lock, flags);
        return 0;
 }