Hi,
It is ' work around' for usb-reset-resume, cause by bug of EM25 or host
controller.
If occurs on runtime suspend, usually by EG25,
If occurs on PM suspend, usually by host controller,
These ' work around' can make user space application recovery as fast as
possible.
But at the same time, increases the complexity of the user space
application
> Aleksander Morgado <[email protected]> writes:
>
> > The people at KDE are working on some patches to better integrate the
> > EG25 under suspend/resume events; they're changing not only power
> > related sysfs attributes, but also patching certain parts of the
> > kernel drivers, including the cdc-wdm driver.
> >
> > https://invent.kde.org/teams/plasma-mobile/issues/-/issues/3
> >
> > Any chance you could take a look at that merge request and provide
> > your own comments on the issue?
>
> The kernel stuff should obviously be reviewed by kernel experts. Not me
> :-)
>
> Anyway, this looks like an attempt to work around a host controller issue by
> making the device driver ignore part of the spec. It might work for this
> specific
> case where the USB device has retained its state, IIUC.
> But that is usually not the case with USB modmes.
>
> The reset_resume logic and background is documented in
> Documentation/driver-api/usb/persist.rst
>
> The solution works fine if both system and device retains state. But modems
> don't
> do that if they lose power during suspend. I believe we have to trust the
> host
> controller, and if it says reset then we have to reset.
>
>
> Bjørn
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