Re: [linux-usb-devel] [PATCH] USB: Only enable autosuspend by default on certain device classes

On 8/3/07, Rogan Dawes <lists@xxxxxxxxxxxx> wrote:
Matthew Garrett wrote:
On Fri, Aug 03, 2007 at 01:44:02PM +0200, Oliver Neukum wrote:
Am Freitag 03 August 2007 schrieb Matthew Garrett:
It's certainly possible to do that, but it's also possible to have a
userspace solution that whitelists devices. The question is whether the
default kernel behaviour should be "Save power, but potentially break
some of my devices" or "Don't break my devices, but use some more
powre".
If both options have drawbacks, IMHO we follow the standard, which
says that devices must support suspension.

Except that lots of hardware doesn't follow the standard in this
respect, otherwise we wouldn't be having this discussion. Personally, I
think "Will break an unknown number of devices" is a significantly
larger drawback than "Will consume a small quantity of additional
power".


I guess the question could be phrased:

Which one is more likely to conclude at some point?

That is, if we blacklist by default, we consume that additional power
indefinitely, because it is unlikely that people will report "my machine
uses 200mW more than I think it should", and thus we are unlikely to
build up knowledge of exactly which devices/classes should be blacklisted.

Compare that to:

"My USB printer broke, guess I'd better report it to LKML".

The first option is unlikely to ever reach a satisfactory conclusion,
whereas the second one is quite likely to flush out the guilty parties
within a relatively short time.

Even though we should be following what the specs says and find other
ways of threating the "messy" devices. A sysfs entry for
enabling/disabling autosuspend and even to add devices to blacklist
seems quite nice to me.


FWIW.

Rogan

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Felipe Balbi
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