On Wed, 1 Sep 2010, Oliver Neukum wrote:
> Oh, there's another little problem in autosuspend_check()
>
> /* Don't allow autosuspend if the device will need
> * a reset-resume and any of its interface drivers
> * doesn't include support or needs remote wakeup.
> */
> if (udev->quirks & USB_QUIRK_RESET_RESUME) {
> struct usb_driver *driver;
>
> driver = to_usb_driver(intf->dev.driver);
> if (!driver->reset_resume ||
> intf->needs_remote_wakeup)
> return -EOPNOTSUPP;
>
> This means devices with this quirk will be suspended.
If all the conditions are met.
> Which in means
> that medium change events will be lost. I think for devices with this quirk
> we can autosuspend only if there's no medium present. Furthermore
> you'll probably need to introduce a new flag to signal this requirement
> to usbcore.
How? usbcore knows nothing about media. The best solution is for
usb-storage to disallow autosuspend if the quirk is set.
> > > > For those buggy readers, it would be better to have something
> > > > which could be implemented as a sysfs attribute in usb-storage.
> > >
> > > Why usb-storage? Any drive for real rotational media has the same
> > > requirement.
> > > Waiting for minutes for a suspend without medium is ridiculous,
> > > as is spinning down a disk after only two seconds.
> >
> > Suggestions for a sysfs interface? Should the sd driver add its own
> > "suspend_delay_no_medium" attribute?
>
> Hm. I see no connection to sd. In fact I see no connection to block
> devices. Tapes have this issue, too.
It could be added for all SCSI devices. But wouldn't it be easier
simply to use a fixed delay when there's no medium? We could pick a
value like 100 ms or make it a module parameter.
There's a problem about communicating the delay value to the PM layer.
The code I'm adding to the PM core assumes a device has only a single
delay: the current suspend_delay value. That current value will be the
one to show up in the "suspend_delay_ms" sysfs attribute. So for
example, you wouldn't be able to set the medium-present delay value at
a time when no media was loaded.
Also, there are potentially problems with drives that take a while to
warm up and claim they have no media in the mean time.
Alan Stern
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