Hi,
Dne 08. 09. 21 v 10:21 Pavel Hofman napsal(a):
Hi,
The current audio gadget has no way to inform the gadget side that the
host side has started playback/capture and that gadget-side alsa
processes should be started.
Playback/capture processes on the host side do not get stuck without the
gadget side consuming/producing data (OUT requests are ignored in
u_audio_iso_complete, IN ones send initial zeros in their req->buf).
However, playback/capture processes on the gadget side get stuck without
the host side sending playback OUT packets or capture IN requests and
time out with error. If there was a way to inform the gadget side that
playback/capture has started on the host side, the gadget clients could
react accordingly.
I drafted a simple patch for u_audio.c which defines read-only boolean
ctl elems "Capture Requested" and "Playback Requested". Their values are
set/reset in methods u_audio_start_capture/playback and
u_audio_stop_capture/playback, i.e. at changes of respective altsettings
from 0 to 1 and back. Every ctl elem value change sends notification via
snd_ctl_notify. The principle works OK for capture/playback start/stop
on the host, as monitored by alsactl:
pi@raspberrypi:~ $ alsactl monitor hw:UAC2Gadget
node hw:UAC2Gadget, #4 (3,0,0,Capture Requested,0) VALUE
node hw:UAC2Gadget, #4 (3,0,0,Capture Requested,0) VALUE
node hw:UAC2Gadget, #3 (3,0,0,Playback Requested,0) VALUE
node hw:UAC2Gadget, #3 (3,0,0,Playback Requested,0) VALUE
However at enumeration the USB host switches both playback and capture
altsettings repeatedly, generating "fake" events from the gadget side
POW. The host even sends regular-sized EP-OUT packets filled with zeros
during enumeration (tested on linux only for now).
Please is there any way to "detect" the enumeration stage to mask out
the "fake" playback/capture start/stop events?
The attached patch does not apply cleanly to mainline u_audio.c because
it's rebased on other patches not submitted yet but it's only a
discussion inducer for now.
Thanks a lot,
Pavel.
diff --git a/drivers/usb/gadget/function/u_audio.c b/drivers/usb/gadget/function/u_audio.c
index e395be32275c..69aef4e3677d 100644
--- a/drivers/usb/gadget/function/u_audio.c
+++ b/drivers/usb/gadget/function/u_audio.c
@@ -34,6 +34,8 @@ enum {
UAC_VOLUME_CTRL,
UAC_CAPTURE_RATE_CTRL,
UAC_PLAYBACK_RATE_CTRL,
+ UAC_CAPTURE_REQ_CTRL,
+ UAC_PLAYBACK_REQ_CTRL,
};
/* Runtime data params for one stream */
@@ -63,6 +65,9 @@ struct uac_rtd_params {
s16 volume_min, volume_max, volume_res;
s16 volume;
int mute;
+ /* playback/capture_is_requested and their state */
+ struct snd_kcontrol *snd_kctl_is_req;
+ int is_requested;
spinlock_t lock; /* lock for control transfers */
@@ -542,6 +547,8 @@ int u_audio_set_playback_srate(struct g_audio *audio_dev, int srate)
}
EXPORT_SYMBOL_GPL(u_audio_set_playback_srate);
+static void update_is_requested(struct uac_rtd_params *prm, unsigned int val);
+
int u_audio_start_capture(struct g_audio *audio_dev)
{
struct snd_uac_chip *uac = audio_dev->uac;
@@ -553,6 +560,7 @@ int u_audio_start_capture(struct g_audio *audio_dev)
struct uac_params *params = &audio_dev->params;
int req_len, i;
+ update_is_requested(&uac->c_prm, 1);
ep = audio_dev->out_ep;
prm = &uac->c_prm;
config_ep_by_speed(gadget, &audio_dev->func, ep);
@@ -625,6 +633,7 @@ void u_audio_stop_capture(struct g_audio *audio_dev)
{
struct snd_uac_chip *uac = audio_dev->uac;
+ update_is_requested(&uac->c_prm, 0);
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);
@@ -645,6 +654,7 @@ int u_audio_start_playback(struct g_audio *audio_dev)
int req_len, i;
unsigned int p_interval, p_pktsize, p_pktsize_residue;
+ update_is_requested(&uac->p_prm, 1);
dev_dbg(dev, "start playback with rate %d\n", params->p_srate_active);
ep = audio_dev->in_ep;
prm = &uac->p_prm;
@@ -711,6 +721,7 @@ void u_audio_stop_playback(struct g_audio *audio_dev)
{
struct snd_uac_chip *uac = audio_dev->uac;
+ update_is_requested(&uac->p_prm, 0);
free_ep(&uac->p_prm, audio_dev->in_ep);
}
EXPORT_SYMBOL_GPL(u_audio_stop_playback);
@@ -1027,6 +1038,27 @@ static int uac_pcm_rate_get(struct snd_kcontrol *kcontrol,
return 0;
}
+static int u_audio_stream_requested_info(struct snd_kcontrol *kcontrol,
+ struct snd_ctl_elem_info *uinfo)
+{
+ uinfo->type = SNDRV_CTL_ELEM_TYPE_BOOLEAN;
+ uinfo->count = 1;
+ uinfo->value.integer.min = 0;
+ uinfo->value.integer.max = 1;
+ uinfo->value.integer.step = 1;
+
+ return 0;
+}
+
+static int u_audio_stream_requested_get(struct snd_kcontrol *kcontrol,
+ struct snd_ctl_elem_value *ucontrol)
+{
+ struct uac_rtd_params *prm = snd_kcontrol_chip(kcontrol);
+ ucontrol->value.integer.value[0] = prm->is_requested;
+ return 0;
+}
+
+
static struct snd_kcontrol_new u_audio_controls[] = {
[UAC_FBACK_CTRL] {
.iface = SNDRV_CTL_ELEM_IFACE_PCM,
@@ -1072,8 +1104,35 @@ static struct snd_kcontrol_new u_audio_controls[] = {
.get = uac_pcm_rate_get,
.private_value = SNDRV_PCM_STREAM_PLAYBACK,
},
+ [UAC_CAPTURE_REQ_CTRL] {
+ .iface = SNDRV_CTL_ELEM_IFACE_PCM,
+ .name = "Capture Requested",
+ .access = SNDRV_CTL_ELEM_ACCESS_READ | SNDRV_CTL_ELEM_ACCESS_VOLATILE,
+ .info = u_audio_stream_requested_info,
+ .get = u_audio_stream_requested_get,
+ .private_value = SNDRV_PCM_STREAM_CAPTURE,
+ },
+ [UAC_PLAYBACK_REQ_CTRL] {
+ .iface = SNDRV_CTL_ELEM_IFACE_PCM,
+ .name = "Playback Requested",
+ .access = SNDRV_CTL_ELEM_ACCESS_READ | SNDRV_CTL_ELEM_ACCESS_VOLATILE,
+ .info = u_audio_stream_requested_info,
+ .get = u_audio_stream_requested_get,
+ .private_value = SNDRV_PCM_STREAM_PLAYBACK,
+ },
};
+static void update_is_requested(struct uac_rtd_params *prm, unsigned int val) {
+ struct snd_kcontrol *kctl = prm->snd_kctl_is_req;
+
+ if (prm->is_requested != val) {
+ prm->is_requested = val;
+ snd_ctl_notify(prm->uac->card, SNDRV_CTL_EVENT_MASK_VALUE,
+ &kctl->id);
+ pr_debug("Setting '%s' to %d", kctl->id.name, val);
+ }
+}
+
int g_audio_setup(struct g_audio *g_audio, const char *pcm_name,
const char *card_name)
{
@@ -1209,6 +1268,38 @@ int g_audio_setup(struct g_audio *g_audio, const char *pcm_name,
err = snd_ctl_add(card, kctl);
if (err < 0)
goto snd_fail;
+
+ kctl = snd_ctl_new1(&u_audio_controls[UAC_PLAYBACK_REQ_CTRL],
+ &uac->p_prm);
+ if (!kctl) {
+ err = -ENOMEM;
+ goto snd_fail;
+ }
+
+ kctl->id.device = pcm->device;
+ kctl->id.subdevice = 0;
+
+ err = snd_ctl_add(card, kctl);
+ if (err < 0)
+ goto snd_fail;
+ (&uac->p_prm)->snd_kctl_is_req = kctl;
+ }
+
+ if (c_chmask) {
+ kctl = snd_ctl_new1(&u_audio_controls[UAC_CAPTURE_REQ_CTRL],
+ &uac->c_prm);
+ if (!kctl) {
+ err = -ENOMEM;
+ goto snd_fail;
+ }
+
+ kctl->id.device = pcm->device;
+ kctl->id.subdevice = 0;
+
+ err = snd_ctl_add(card, kctl);
+ if (err < 0)
+ goto snd_fail;
+ (&uac->c_prm)->snd_kctl_is_req = kctl;
}
for (i = 0; i <= SNDRV_PCM_STREAM_LAST; i++) {
