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

[Simon Glass]

Hi Shantur,

On Sun, 19 Nov 2023 at 15:47, Shantur Rathore <i at shantur.com> wrote:
>
> 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?

Yes, that is correct. The dm_remove_devices_flags() call should do
that. The code in bootm_disable_interrupts() is a hangover from the
pre-driver model days, I suspect.

Perhaps we should also remove the eth_halt() and usb_pause() from
bootm_disable_interrupts() ?

Regards,
Simon