Re: [PATCH] eeepc-laptop: enable camera by default

From: Alan Stern
Date: Mon Jun 08 2009 - 16:44:58 EST


On Mon, 8 Jun 2009, Matthew Garrett wrote:

> On Sun, Jun 07, 2009 at 11:10:52PM -0400, Alan Stern wrote:
> > On Mon, 8 Jun 2009, Matthew Garrett wrote:
> >
> > > On Sun, Jun 07, 2009 at 11:03:48PM -0400, Alan Stern wrote:
> > >
> > > > There's no mechanism for this. It many environments it couldn't work,
> > > > because the decision about whether to enable autosuspend is made when
> > > > the device is first created (i.e., when the creation uevent is
> > > > received), whereas driver binding doesn't occur until later.
> > >
> > > There's a lot of power management situations where you don't end up with
> > > the optimal power configuration until a driver's bound. It's certainly
> > > possible to do this in userspace, but if we know that the hardware
> > > supported by a given driver will always work then it seems reasonable to
> > > have it whitelist autosuspend on that device.
> >
> > Sure. Such a thing could be added easily enough. It just doesn't
> > exist now, that's all.
>
> Something roughly like this? We'd probably also want a function call so
> drivers can do it based on the ID of the device they're handling, but in
> some cases we can probably assume that all devices supported by the
> driver will work.

My preference would be to use a function call always, rather than
relying on static driver information. It provides more flexibility.

> diff --git a/drivers/usb/core/driver.c b/drivers/usb/core/driver.c
> index d0a21a5..36f63a7 100644
> --- a/drivers/usb/core/driver.c
> +++ b/drivers/usb/core/driver.c
> @@ -355,6 +355,8 @@ int usb_driver_claim_interface(struct usb_driver *driver,
> iface->condition = USB_INTERFACE_BOUND;
> mark_active(iface);
> iface->pm_usage_cnt = !(driver->supports_autosuspend);
> + if (driver->supports_autosuspend && driver->enable_autosuspend)
> + udev->autosuspend_disabled=0;

Style violation: You should have blanks around the '=' sign. :-)

> usb_pm_unlock(udev);

That's right. If implemented as a function, turning off
udev->autosuspend_disabled is all the function would need to do
(provided we add the restriction that it should never be called from
anywhere except inside a driver's probe routine).

Alan Stern

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