Unable to use struct usb_endpoint_descriptor in FunctionFS

["Sid Spry" <sid@aeam.us>]

Hello, I've figured out how to get my userspace driver code to enumerate for
the host and send/receive from the device with bulk endpoints as demonstrated
in ffs-test.c. I have successfully added another bulk endpoint, but issues
arise when I try to add an isochronous endpoint.

I've tracked the problem, I think, to the mere presence of the struct
usb_endpoint_descriptor. Is anyone able to elucidate what I might be missing?

The rejected set of descriptors follows. Note I set the usb_endpoint_descriptor
struct to be a bulk endpoint; I expect the extra fields would be ignored.

I can provide the full code if helpful. Superspeed descriptors commented out
as I'm less familiar with USB3 and I found that the fs/hs/ss descriptor sets had
to be equivalent.

```
static const struct {
	struct usb_functionfs_descs_head_v2 header;
	__le32 fs_count;
	__le32 hs_count;
	//__le32 ss_count;
	struct {
		struct usb_interface_descriptor intf;
		struct usb_endpoint_descriptor_no_audio sink;
		struct usb_endpoint_descriptor_no_audio source;
		struct usb_endpoint_descriptor iso_sink;
	} __attribute__((packed)) fs_descs, hs_descs;
	/*struct {
		struct usb_interface_descriptor intf;
		struct usb_endpoint_descriptor_no_audio sink;
		struct usb_ss_ep_comp_descriptor sink_comp;
		struct usb_endpoint_descriptor_no_audio source;
		struct usb_ss_ep_comp_descriptor source_comp;
	} ss_descs;*/
} __attribute__((packed)) descriptors = {
	.header = {
		.magic  = cpu_to_le32(FUNCTIONFS_DESCRIPTORS_MAGIC_V2),
		.length = cpu_to_le32(sizeof descriptors),
		.flags  = cpu_to_le32(FUNCTIONFS_HAS_FS_DESC |
				     FUNCTIONFS_HAS_HS_DESC), // |
				     //FUNCTIONFS_HAS_SS_DESC),
	},
	.fs_count = cpu_to_le32(4),
	.hs_count = cpu_to_le32(4),
	//.ss_count = cpu_to_le32(5),
	.fs_descs = {
		.intf = {
			.bLength = sizeof descriptors.fs_descs.intf,
			.bDescriptorType = USB_DT_INTERFACE,
			.bNumEndpoints = 2,
			.bInterfaceClass = USB_CLASS_VENDOR_SPEC,
			.iInterface = 1,
		},
		.sink = {
			.bLength = sizeof descriptors.fs_descs.sink,
			.bDescriptorType = USB_DT_ENDPOINT,
			.bEndpointAddress = 1 | USB_DIR_IN,
			.bmAttributes = USB_ENDPOINT_XFER_BULK,
			/* .wMaxPacketSize = autoconfiguration (kernel) */
		},
		.source = {
			.bLength = sizeof descriptors.fs_descs.source,
			.bDescriptorType = USB_DT_ENDPOINT,
			.bEndpointAddress = 2 | USB_DIR_OUT,
			.bmAttributes = USB_ENDPOINT_XFER_BULK,
			/* .wMaxPacketSize = autoconfiguration (kernel) */
		},
		.iso_sink = {
			.bLength = sizeof descriptors.fs_descs.iso_sink,
			.bDescriptorType = USB_DT_ENDPOINT,
			.bEndpointAddress = 3 | USB_DIR_OUT,
			.bmAttributes = USB_ENDPOINT_XFER_BULK,
		},
	},
	.hs_descs = {
		.intf = {
			.bLength = sizeof descriptors.fs_descs.intf,
			.bDescriptorType = USB_DT_INTERFACE,
			.bNumEndpoints = 3,
			.bInterfaceClass = USB_CLASS_VENDOR_SPEC,
			.iInterface = 1,
		},
		.sink = {
			.bLength = sizeof descriptors.hs_descs.sink,
			.bDescriptorType = USB_DT_ENDPOINT,
			.bEndpointAddress = 1 | USB_DIR_IN,
			.bmAttributes = USB_ENDPOINT_XFER_BULK,
			.wMaxPacketSize = cpu_to_le16(512),
		},
		.source = {
			.bLength = sizeof descriptors.hs_descs.iso_sink,
			.bDescriptorType = USB_DT_ENDPOINT,
			.bEndpointAddress = 2 | USB_DIR_OUT,
			.bmAttributes = USB_ENDPOINT_XFER_BULK,
			.wMaxPacketSize = cpu_to_le16(512),
			.bInterval = 1,
		},
		.iso_sink = {
			.bLength = sizeof descriptors.hs_descs.source,
			.bDescriptorType = USB_DT_ENDPOINT,
			.bEndpointAddress = 3 | USB_DIR_OUT,
			.bmAttributes = USB_ENDPOINT_XFER_BULK,
			.wMaxPacketSize = cpu_to_le16(512),
			.bInterval = 1,
		},

	},
	/*.ss_descs = {
		.intf = {
			.bLength = sizeof descriptors.fs_descs.intf,
			.bDescriptorType = USB_DT_INTERFACE,
			.bNumEndpoints = 2,
			.bInterfaceClass = USB_CLASS_VENDOR_SPEC,
			.iInterface = 1,
		},
		.sink = {
			.bLength = sizeof descriptors.hs_descs.sink,
			.bDescriptorType = USB_DT_ENDPOINT,
			.bEndpointAddress = 1 | USB_DIR_IN,
			.bmAttributes = USB_ENDPOINT_XFER_BULK,
			.wMaxPacketSize = cpu_to_le16(1024),
		},
		.sink_comp = {
			.bLength = USB_DT_SS_EP_COMP_SIZE,
			.bDescriptorType = USB_DT_SS_ENDPOINT_COMP,
			.bMaxBurst = 0,
			.bmAttributes = 0,
			.wBytesPerInterval = 0,
		},
		.source = {
			.bLength = sizeof descriptors.hs_descs.source,
			.bDescriptorType = USB_DT_ENDPOINT,
			.bEndpointAddress = 2 | USB_DIR_OUT,
			.bmAttributes = USB_ENDPOINT_XFER_BULK,
			.wMaxPacketSize = cpu_to_le16(1024),
			.bInterval = 1,
		},
		.source_comp = {
			.bLength = USB_DT_SS_EP_COMP_SIZE,
			.bDescriptorType = USB_DT_SS_ENDPOINT_COMP,
			.bMaxBurst = 0,
			.bmAttributes = 0,
			.wBytesPerInterval = 0,
		},
	},*/
};
```

Cheers!