[PATCH v5 05/12] usb: Avoid unbinding devices in use by bootflows

[Shantur Rathore]

Hi Simon,

On Sun, Nov 19, 2023 at 7:12 PM Simon Glass <sjg at chromium.org> wrote:
>
> When a USB device is unbound, it causes any bootflows attached to it to
> be removed, via a call to bootdev_clear_bootflows() from
> bootdev_pre_unbind(). This obviously makes it impossible to boot the
> bootflow.
>
> However, when booting a bootflow that relies on USB, usb_stop() is
> called, which unbinds the device. At that point any information
> attached to the bootflow is dropped.
>
> This is quite risky since the contents of freed memory are not
> guaranteed to remain unchanged. Depending on what other options are
> done before boot, a hard-to-find bug may crop up.
>
> There is no need to unbind all the USB devices just to quiesce them.
> Add a new usb_pause() call which removes them but leaves them bound.
>

I am no UEFI / bootloader expert and while trying to gather more info
on EFI ExitBootServies I came across this
https://github.com/tianocore-docs/edk2-UefiDriverWritersGuide/blob/master/7_driver_entry_point/77_adding_the_exit_boot_services_feature.md

If I understand this correctly, EFI ( U-boot in this case) should be
halting all USB controllers like done in usb_stop()
Is my understanding correct?

 Kind regards
Shantur