Re: [PATCH V2] usb: gadget: f_uac1: add adaptive sync support for capture
From: Pavel Hofman
Date: Wed Oct 25 2023 - 02:44:59 EST
Dne 24. 10. 23 v 12:14 be286 napsal(a):
Hi Pavel,
Feedback endpoint works for uca1 capture, means "EPOUT_EN".
Charles Yi
Hi Charles,
Sorry for my mistake, I thought you were implementing adaptive mode for
EP-IN.
IIUC now your patch adds asynchronous mode (not adaptive sync) to UAC1
EP OUT, in the same way as implemented in UAC2.
IIUC your patch also changes the UAC1 EP-OUT default mode from adaptive
to asynchronous via
+#define UAC1_DEF_CSYNC USB_ENDPOINT_SYNC_ASYNC
The current (the only supported) mode is adaptive
https://elixir.bootlin.com/linux/latest/source/drivers/usb/gadget/function/f_uac1.c#L214:
/* Standard ISO OUT Endpoint Descriptor */
static struct usb_endpoint_descriptor as_out_ep_desc = {
.bLength = USB_DT_ENDPOINT_AUDIO_SIZE,
.bDescriptorType = USB_DT_ENDPOINT,
.bEndpointAddress = USB_DIR_OUT,
.bmAttributes = USB_ENDPOINT_SYNC_ADAPTIVE
| USB_ENDPOINT_XFER_ISOC,
.wMaxPacketSize = cpu_to_le16(UAC1_OUT_EP_MAX_PACKET_SIZE),
.bInterval = 4,
};
IMO the patch should keep the adaptive mode as default, to maintain
compatibility with user setups.
With regards,
Pavel.
At 2023-10-18 17:52:20, "Pavel Hofman" <pavel.hofman@xxxxxxxxxxx> wrote:
Dne 18. 10. 23 v 9:47 Charles Yi napsal(a):
UAC1 has it's own freerunning clock and can update Host about
real clock frequency through feedback endpoint so Host can align
number of samples sent to the UAC1 to prevent overruns/underruns.
Change UAC1 driver to make it configurable through additional
'c_sync' configfs file.
Default remains 'asynchronous' with possibility to switch it
to 'adaptive'.
Hi Charles,
Please can you clarify more the adaptive EP IN scenario? I am aware that
the f_uac2.c also allows defining c_sync type (that's what your patch is
based on).
IIUC the data production rate of adaptive source endpoint (i.e. EP IN)
is controlled by feed forward messages from the host
Quoting http://sdpha2.ucsd.edu/Lab_Equip_Manuals/usb_20.pdf page 73:
"Adaptive source endpoints produce data at a rate that is controlled by
the data sink. The sink provides feedback (refer to Section 5.12.4.2) to
the source, which allows the source to know the desired data rate of the
sink."
While the current f_uac2 implementation generates feedback for EP OUT
async (unlike f_uac1), I cannot find any support for incoming
feed-forward messages from the host for EP IN adaptive case. Neither in
f_uac1, of course.
I am not sure if linux supports IN EP adaptive, but the MS UAC2 driver
does not
https://learn.microsoft.com/en-us/windows-hardware/drivers/audio/usb-2-0-audio-drivers#audio-streaming:
"For the Adaptive IN case the driver doesn't support a feed forward
endpoint. If such an endpoint is present in the alternate setting, it
will be ignored. The driver handles the Adaptive IN stream in the same
way as an Asynchronous IN stream."
IIUC (and I may be wrong) all the c_sync param does in f_uac2 (and
f_uac1 in your patch) is just changing the EP IN configuration flag, but
the actual support for truly adaptive EP IN is not implemented. IMO
there is no code which would accept the feed-forward message from the
host and adjust the rate at which samples are consumed from the alsa
buffer to EP IN packets (method u_audio_iso_complete
https://elixir.bootlin.com/linux/latest/source/drivers/usb/gadget/function/u_audio.c#L193
)
That pertains a bit to the first sentence of your patch - IMO it
describes EP OUT async, but not EP IN adaptive.
Thanks a lot for a bit of clarification.
Pavel.
Changes in V2:
- Updated the indentation of commit message.
Signed-off-by: Charles Yi <be286@xxxxxxx>
---
drivers/usb/gadget/function/f_uac1.c | 30 ++++++++++++++++++++++++++++
drivers/usb/gadget/function/u_uac1.h | 2 ++
2 files changed, 32 insertions(+)
diff --git a/drivers/usb/gadget/function/f_uac1.c b/drivers/usb/gadget/function/f_uac1.c
index 6f0e1d803dc2..7a6fcb40bb46 100644
--- a/drivers/usb/gadget/function/f_uac1.c
+++ b/drivers/usb/gadget/function/f_uac1.c
@@ -33,6 +33,8 @@
#define FUOUT_EN(_opts) ((_opts)->c_mute_present \
|| (_opts)->c_volume_present)
+#define EPOUT_FBACK_IN_EN(_opts) ((_opts)->c_sync == USB_ENDPOINT_SYNC_ASYNC)
+
struct f_uac1 {
struct g_audio g_audio;
u8 ac_intf, as_in_intf, as_out_intf;
@@ -227,6 +229,16 @@ static struct uac_iso_endpoint_descriptor as_iso_out_desc = {
.wLockDelay = cpu_to_le16(1),
};
+static struct usb_endpoint_descriptor as_fback_ep_desc = {
+ .bLength = USB_DT_ENDPOINT_SIZE,
+ .bDescriptorType = USB_DT_ENDPOINT,
+
+ .bEndpointAddress = USB_DIR_IN,
+ .bmAttributes = USB_ENDPOINT_XFER_ISOC | USB_ENDPOINT_USAGE_FEEDBACK,
+ .wMaxPacketSize = cpu_to_le16(3),
+ .bInterval = 1,
+};
+
static struct uac_format_type_i_discrete_descriptor as_in_type_i_desc = {
.bLength = 0, /* filled on rate setup */
.bDescriptorType = USB_DT_CS_INTERFACE,
@@ -280,6 +292,7 @@ static struct usb_descriptor_header *f_audio_desc[] = {
(struct usb_descriptor_header *)&as_out_ep_desc,
(struct usb_descriptor_header *)&as_iso_out_desc,
+ (struct usb_descriptor_header *)&as_fback_ep_desc,
(struct usb_descriptor_header *)&as_in_interface_alt_0_desc,
(struct usb_descriptor_header *)&as_in_interface_alt_1_desc,
@@ -1107,6 +1120,9 @@ static void setup_descriptor(struct f_uac1_opts *opts)
f_audio_desc[i++] = USBDHDR(&as_out_type_i_desc);
f_audio_desc[i++] = USBDHDR(&as_out_ep_desc);
f_audio_desc[i++] = USBDHDR(&as_iso_out_desc);
+ if (EPOUT_FBACK_IN_EN(opts)) {
+ f_audio_desc[i++] = USBDHDR(&as_fback_ep_desc);
+ }
}
if (EPIN_EN(opts)) {
f_audio_desc[i++] = USBDHDR(&as_in_interface_alt_0_desc);
@@ -1317,6 +1333,12 @@ static int f_audio_bind(struct usb_configuration *c, struct usb_function *f)
ac_header_desc->baInterfaceNr[ba_iface_id++] = status;
uac1->as_out_intf = status;
uac1->as_out_alt = 0;
+
+ if (EPOUT_FBACK_IN_EN(audio_opts)) {
+ as_out_ep_desc.bmAttributes =
+ USB_ENDPOINT_XFER_ISOC | USB_ENDPOINT_SYNC_ASYNC;
+ as_out_interface_alt_1_desc.bNumEndpoints++;
+ }
}
if (EPIN_EN(audio_opts)) {
@@ -1354,6 +1376,12 @@ static int f_audio_bind(struct usb_configuration *c, struct usb_function *f)
goto err_free_fu;
audio->out_ep = ep;
audio->out_ep->desc = &as_out_ep_desc;
+ if (EPOUT_FBACK_IN_EN(audio_opts)) {
+ audio->in_ep_fback = usb_ep_autoconfig(gadget, &as_fback_ep_desc);
+ if (!audio->in_ep_fback) {
+ goto err_free_fu;
+ }
+ }
}
if (EPIN_EN(audio_opts)) {
@@ -1685,6 +1713,8 @@ static struct usb_function_instance *f_audio_alloc_inst(void)
opts->req_number = UAC1_DEF_REQ_NUM;
+ opts->c_sync = UAC1_DEF_CSYNC;
+
snprintf(opts->function_name, sizeof(opts->function_name), "AC Interface");
return &opts->func_inst;
diff --git a/drivers/usb/gadget/function/u_uac1.h b/drivers/usb/gadget/function/u_uac1.h
index f7a616760e31..c6e2271e8cdd 100644
--- a/drivers/usb/gadget/function/u_uac1.h
+++ b/drivers/usb/gadget/function/u_uac1.h
@@ -27,6 +27,7 @@
#define UAC1_DEF_MAX_DB 0 /* 0 dB */
#define UAC1_DEF_RES_DB (1*256) /* 1 dB */
+#define UAC1_DEF_CSYNC USB_ENDPOINT_SYNC_ASYNC
struct f_uac1_opts {
struct usb_function_instance func_inst;
@@ -56,6 +57,7 @@ struct f_uac1_opts {
struct mutex lock;
int refcnt;
+ int c_sync;
};
#endif /* __U_UAC1_H */