I have the same issue, too.
I found some article but still not solve the issue. I have trawled through many articles with no luck.
I post it.
g_multi.ko needs driver. Windows shows up as an unknow device "Multifunction Composite Gadget". I need a HID and a mass storage.
HID is work OK. But mass storage is still not work at all. log as below:
root@imx6ull14x14evk:~# modprobe dummy_hcd
dummy_hcd dummy_hcd.0: USB Host+Gadget Emulator, driver 02 May 2005
dummy_hcd dummy_hcd.0: Dummy host controller
dummy_hcd dummy_hcd.0: new USB bus registered, assigned bus number 1
hub 1-0:1.0: USB hub found
hub 1-0:1.0: 1 port detected
2188000.ethernet supply phy not found, using dummy regulator
root@imx6ull14x14evk:~# pps pps0: new PPS source ptp0
alloc_contig_range: [8c058, 8c060) PFNs busy
2188000.ethernet supply phy not found, using dummy regulator
pps pps0: new PPS source ptp0
alloc_contig_range: [8c058, 8c060) PFNs busy
root@imx6ull14x14evk:~#
root@imx6ull14x14evk:~# modprobe g_hid
2188000.ethernet supply phy not found, using dummy regulator
pps pps0: new PPS source ptp0
alloc_contig_range: [8c058, 8c060) PFNs busy
g_hid gadget: HID Gadget, version: 2010/03/16
g_hid gadget: g_hid ready
root@imx6ull14x14evk:~# g_hid gadget: high-speed config #1: HID Gadget
root@imx6ull14x14evk:~#
root@imx6ull14x14evk:~# modprobe g_mass_storage file=/dev/mmcblk1
Mass Storage Function, version: 2009/09/11
LUN: removable file: (no medium)
LUN: file: /dev/mmcblk1
Number of LUNs=1
g_mass_storage gadget: Mass Storage Gadget, version: 2009/09/11
g_mass_storage gadget: userspace failed to provide iSerialNumber
g_mass_storage gadget: g_mass_storage ready
root@imx6ull14x14evk:~# usb 1-1: new high-speed USB device number 2 using dummy_hcd
g_mass_storage gadget: high-speed config #1: Linux File-Backed Storage
usb-storage 1-1:1.0: USB Mass Storage device detected
usb-storage 1-1:1.0: Quirks match for vid 0525 pid a4a5: 10000
scsi host0: usb-storage 1-1:1.0
2188000.ethernet supply phy not found, using dummy regulator
pps pps0: new PPS source ptp0
alloc_contig_range: [8c058, 8c060) PFNs busy
scsi 0:0:0:0: Direct-Access Linux File-Stor Gadget 0409 PQ: 0 ANSI: 2
2188000.ethernet supply phy not found, using dummy regulator
pps pps0: new PPS source ptp0
alloc_contig_range: [8c058, 8c060) PFNs busy
sd 0:0:0:0: [sda] 7405568 512-byte logical blocks: (3.79 GB/3.53 GiB)
sd 0:0:0:0: [sda] Write Protect is off
sd 0:0:0:0: [sda] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA
sda: sda1 sda2 sda3 sda4
sd 0:0:0:0: [sda] Attached SCSI disk
root@imx6ull14x14evk:~#
root@imx6ull14x14evk:~# lsusb
Bus 001 Device 002: ID 0525:a4a5 Netchip Technology, Inc. Pocketbook Pro 903
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub