On Wednesday 10 June 2009, Alan Stern wrote: > On Wed, 10 Jun 2009, Rafael J. Wysocki wrote: > > > > By the way, a legitimate reason for aborting an autosuspend is if the > > > device's driver requires remote wakeup to be enabled during suspend but > > > the user has disabled it. > > > > Do you mean the user has disabled the remote wakeup? > > Yes, by writing to the power/wakeup attribute. > > > > > > > There should be a sysfs interface (like the one in USB) to allow > > > > > userspace to prevent a device from being autosuspended -- and perhaps > > > > > also to force it to be suspended. > > > > > > > > To prevent a device from being suspended - yes. To force it to stay suspended > > > > - I'm not sure. > > > > > > I'm not sure either. Oliver Neukum requested it originally and it has > > > been useful for debugging, but I haven't seen many places where it > > > would come in useful in practice. > > I did think of one use for this feature. It's unique to USB, > however... > > In Windows, you're not supposed to unplug a hot-unpluggable device > without first telling the OS -- there's a "Safely Remove Hardware" > applet. When you tell the applet you want to remove a USB device, the > system disables the device's port and then says it's okay to unplug the > device. Now Linux doesn't have any user API for disabling USB ports, > but suspending a port has the same effect (the device can't distinguish > a disable from a suspend). > > It turns out that some devices (MP3 players, for instance) have > incorporated this into their design. They display a "Safe to unplug" > message when their port is disabled or suspended. People like to see > this message -- it makes them feel good about unplugging the device -- > and the only way to get it under Linux is by forcing the device to be > suspended. :-) Well, I'd very much prefer to have a separate mechanism for that. > > The problem with it is that the user space may not know if it is safe to keep > > a device suspended and if it is not, the kernel will have to ignore the setting > > anyway, so I'm not sure what's the point (except for debugging). > > This falls into the category of "The user knows better". If the user > specifically tells the kernel to suspend a device (rather than just > letting it autosuspend), and this causes a problem, then it's the > user's own fault. > > After all, who's really the master? Us or the kernel? Oh, that depends on who the user is. If I'm the user, I'm the master, but in case of a typical Windows user I'm afraid the kernel has to know better. ;-) Best, Rafael _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
