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SubjectRe: Flames over -- Re: Which is simpler?
David Brownell wrote:
> No, not "AFAIK" ... since when I told you explicitly that was untrue,
> you then ignored that statement. And didn't look at the specs that
> I pointed you towards, which provide the details. (USB 2.0 spec re
> hubs; and of course the Linux-USB hub driver ... www.usb.org)

I ignored nothing. I fully accepted your explanation as true and
pointed out that it changes nothing; data loss in this perfectly valid
use case just because the kernel can not be absolutely certain the user
did not do something stupid while suspended is unacceptable.

>
> The events that a hub receives say pretty exactly what happened.
> You should know that already, since USB behaves that way even
> when the system is _not_ suspended ...
>

How it behaves while running and how it behaves while suspended are
usually two very different things.

> The full mechanism for USB is more like wakeup signaling on USB triggering
> hub wakeup (possibly cascading through a few layers of external hub), at
> some point triggering root hub wakeup, which maps to a PME# signal. That
> relies on no more than VBUS being powered at a fraction of a milliAmpere,
> and the equivalent of a pair of voltage comparators triggering wakeup when
> USB signaling changes from J to K states for something like 10 msec.
>
>
>
> Did you read about the PME# signal in the PCI PM spec? www.pci-sig.com
> Maybe you could try that.
>

No, I took your word for it without protest as it doesn't change my main
argument: data loss in the face of normal usage is not acceptable.
Claiming that it has to be this way because the alternative _might_
result in data loss in the worst (mis)use case is an untenable position.


> Also the ACPI spec ... the early chapters give a decent overview of the
> different components of that model. (ISTR two chapters try that, with
> the second being more to-the-point despite some duplicated graphics.)
>
> - Dave
>
>
>

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