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    SubjectRe: 2.4.22 USB problem (uhci)
    On Fri, Sep 19, 2003 at 02:14:49PM -0700, Jan Rychter wrote:
    > >>>>> "Greg" == Greg KH <> writes:
    > Greg> On Fri, Sep 19, 2003 at 01:29:55PM -0700, Jan Rychter wrote: If
    > Greg> you want to suspend using 2.4, unload the usb drivers entirely.
    > Greg> That's the only safe way.
    > >>
    > >> I wasn't talking about suspending, but about processor
    > >> C-states. These are power states that the mobile processors enter
    > >> dynamically, many times a second. In my case:
    > Greg> Ah, sorry. I'm getting D and C states mixed up here.
    > [...]
    > You probably mean S-states, which are for sleep.

    Ugh, ok, I give up :)

    > >> As you can see, C3 (lowest power) is being used a lot. This makes my
    > >> laptop run cool. If I use usb-uhci, the processor is never able to
    > >> go into C3 because of DMA activity. uhci is better, because it at
    > >> least permits me to use C3 when there are no devices plugged in.
    > >>
    > >> And going back to the uhci problem... ?
    > Greg> UHCI by design sucks massive PCI bandwidth. There is logic in
    > Greg> the uhci drivers that try to help this out by reducing
    > Greg> transactions when not much is going on, but there's only so much
    > Greg> we can do in software, sorry. I'm guessing that you aren't going
    > Greg> to be able to change this.
    > Greg> Unless you go buy a ohci usb cardbus controller card :)
    > Now you've confused me.
    > Do your comments above apply to "uhci" or "usb-uhci"?
    > Please allow me to restate the original problem:
    > -- I usually use uhci instead of usb-uhci, because it is able to go
    > into "suspend mode" when no devices are plugged, which allows the
    > CPU to enter C3 states,
    > -- usb-uhci eats CPU power by keeping it in C2 constantly because of
    > busmastering DMA activity, therefore being much less useful,
    > -- uhci generally works for me just fine, but breaks in one particular
    > case, when removing the device causes a strange message to be
    > printed and the system being unable to use the C3 states again,
    > until uhci is unloaded and reloaded back again.
    > Just as a reminder, this message is:
    > uhci.c: efe0: host controller halted. very bad
    > I hope if the message says "very bad", then this is something that can
    > be fixed. I was therefore reporting a problem with "uhci" and kindly
    > asking for help.

    Ok, sorry for the confusion. No I don't know of a fix for this problem,
    but one just went into the 2.6 kernel tree for the uhci-hcd driver that
    you might want to take a look at that fixed a problem almost exactly
    like this.


    greg k-h
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