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. :-) > 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? Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
