linux-kernel - Re: [PATCH] usb: xhci: Disable runtime PM suspend for quirky controllers.

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Date:	Wed, 29 May 2013 12:38:28 -0700
From:	Sarah Sharp <sarah.a.sharp@...ux.intel.com>
To:	Julius Werner <jwerner@...omium.org>
Cc:	Shawn Nematbakhsh <shawnn@...omium.org>,
	Alan Stern <stern@...land.harvard.edu>,
	linux-usb@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Don Zickus <dzickus@...hat.com>,
	Oliver Neukum <oliver@...kum.org>
Subject: Re: [PATCH] usb: xhci: Disable runtime PM suspend for quirky
 controllers.

On Tue, May 28, 2013 at 02:41:18PM -0700, Julius Werner wrote:
> The policy we want to achieve is to disable runtime PM iff there is a
> device connected that doesn't have persist_enabled or a reset_resume()
> handler and whose parent/root hub resets on resume, right?

Makes sense.  However, not all distros may want that policy, so there
should be a way to change that policy via sysfs.  Some distros may
choose to take the power savings over having a particular USB device
work, especially in the server market.

Don, Oliver, what do you think of this patch:
http://marc.info/?l=linux-usb&m=136941922715772&w=2

Julius is proposing to limit the scope of the patch a bit, but the
impact will still be that TI hosts will be active more often than not.

> So couldn't
> we remove the HCD-specific XHCI_RESET_ON_RESUME and set the (existing)
> generic USB_QUIRK_RESET_RESUME on the root hub instead?  Then we could
> handle all of this in the USB core (during device initialization and
> when changing persist_enabled through sysfs) by just checking for
> udev->reset_resume on all parent hubs of the device in question (and
> use pm_runtime_get/put() on said device to prevent its parents from
> suspending as appropriate).

Alan, what happens if we set USB_QUIRK_RESET_RESUME on the roothub?
I don't think that currently translates into the host controller's Reset
register getting written, which is what I think Julius is proposing.

Sarah Sharp
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