Hi Pavel, Feedback endpoint works for uca1 capture, means "EPOUT_EN". Charles Yi 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 */
