Re: Runtime PM defaults for USB hosts

[Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>]

On Mon, 6 Aug 2012, Sarah Sharp wrote:

> Hi Alan and Rafael,
> 
> Is there a reason why runtime PM is disabled by default for PCI USB host
> controllers?  It would really be nice to have this turned on by default
> at boot, rather than running udev scripts or powertop.

As far as I know, the only reason is that runtime PM is disabled by
default for _all_ devices, unless the subsystem or driver specifically
enables it.  Nobody has submitted a patch enabling runtime PM for PCI
USB host controllers.

> Are there PCI USB hosts that can't handle D3?  Or something else
> preventing us from turning runtime PM on by default?

I'm not aware of any such problems.  But that doesn't mean they don't 
exist -- it wouldn't be surprising if you start getting complaints when 
you enable runtime PM by default.

I guess the only way to find out is to try.  It's not a hard change; 
just call pm_runtime_allow(&dev->dev) just before the normal return in 
usb_hcd_pci_probe().

Alan Stern

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