usb gadget failure when chain loading

[99degree]

No matter how chain loading happened, the usb gadget fail as result.

fail cases:
abl->recovery->kexec->recovery
abl->uboot->recovery
abl->uboot->AOSP

success case:
abl->uboot->recovery(g_serial)

All case are failure. So most likely need to workaround in kernel usb stack.
(EDIT: some success case is found)

[99degree]

according to wireshark, the "GET DESCRIPTOR" response is all zero. blength is 0.

[99degree]

chainloading to los boot.img is somewhat working to show up adb device but no adb connection. so it is more likely a mainline kernel to workaround it.

[99degree]

there is a proof that both u-boot and mainline kernel is doing fine. Here is the setup.

(1) compile kernel with usb gadget serial mode.
│ Defined at drivers/usb/gadget/legacy/Kconfig:291 │
│ Prompt: Serial Gadget (with CDC ACM and CDC OBEX support) │
│ Depends on: USB_SUPPORT [=y] && USB_GADGET [=y] && TTY [=y] │
│ Location: │
│ -> Device Drivers │
│ -> USB support (USB_SUPPORT [=y]) │
│ -> USB Gadget Support (USB_GADGET [=y]) │
│ -> USB Gadget precomposed configurations │
│ -> Serial Gadget (with CDC ACM and CDC OBEX support) (USB_G_SERIAL [=y])

as above, gserial is mandated the setup even usb configfs also compiles in.

(2) add androidboot.console=ttyGS0 into boot parameter of boot.img, aka fastboot,
(3) boot into u-boot's fastboot, and waiting for chainloading android img at step 2.
(4) do fastboot android boot of step 2.
(5) open putty and select session->connection_type->serial and then check the com port from host machine device manager, aka com9, then hit open

thus a serial console is shown up. that also eliminates the need for adb. but it is not as flexible as adb. so both u-boot and kernel usb stack is working fine.

[99degree]

refer to today next branch https://github.com/99degree/linux/tree/working-20250623
a module parmeter is added to gserial and g_ncm. that can force to fail loading these module so configfs/functionfs can get probe successfully even through pre-compiled in that said (g_ncm/gserial) module.

the name of param is gserial.mod_enable and g_ncm.enable if set to 0 then both module probe fail and fallover to configfs/functionfs counterpart.

[99degree]

if met the case of usb fail init at win11 device manager, then gserial can take back control for grep log