Date:   Wed, 25 Oct 2023 08:44:49 +0200
From:   Pavel Hofman <pavel.hofman@...tera.com>
To:     be286 <be286@....com>
Cc:     gregkh@...uxfoundation.org, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2] usb: gadget: f_uac1: add adaptive sync support for
 capture

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@...tera.com> 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@....com>
>>> ---
>>>    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 */

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