Re: [linux-usb-devel] error to be returned while suspended

Hi!

OK, let me state the basics.

To get real power savings, we:
- blank the display
- spin down the hard drive
- put the CPU into an ACPI sleep state

To do the latter well, we need to make sure there's no DMA. It is
important that less or little DMA will not help. We need no DMA.
So we need to handle the commonest scenarios fully.

I dare say that the commonest scenario involving USB is a laptop with
an input device attached. Input devices are for practical purposes always
opened. A simple resume upon open and suspend upon close is useless.

Okay, but you can simply do autosuspend with remote wakeup completely
inside input driver. You do ot need it to be controlled from X... at
most you need one variable ('autosuspend_inactivity_timeout')
controlled from userland.

That's what we already do for hdd spindown... you simply tell disk to
aitospindown after X seconds of inactivity.

The firmware in the drive supplies this function. It's hardly by choice
that it is made available. The power management functions without
timeout are also exported. For other power control features like
cpu frequency considerable effort has been made to export them to
user space.

A simple timeout solution has drawbacks.

- there's no guarantee the user wants wakeup (think laptop on
crowded table)

If you do not want wakeups (=> do not want any input from that
device), then close that device.

- you want to suspend immediately when you blank the screen (or switch to
a text console)

I kind-of understand "when you blank", but I do not think this
mandatory. Why would you want to suspend when switching to text
console? Am I no longer allowed to use gpm?

- you want to consider all devices' activity. I am not pleased if my mouse
becomes less responsive just because I used only the keyboard for a
few minutes. Coordinating this inside the driver is hard as some input
devices might well be not usb (eg. bluetooth mouse, usb tablet)

Yep, that would be nice; but not at price of /sys/.../power/state like
monstrosity that never ever worked properly.
Pavel
--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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