Re:Re: [PATCH V2] usb: gadget: f_uac1: add adaptive sync support for capture

[be286]

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 */