linux-kernel - RE: USB remote wakeup through gpio interrupt

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Date:	Thu, 6 Mar 2014 04:54:58 +0000
From:	Peter Chen <Peter.Chen@...escale.com>
To:	Alan Stern <stern@...land.harvard.edu>,
	Jagdish Gedia <jvgediya@...il.com>
CC:	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: USB remote wakeup through gpio interrupt

 
> 
> > Hi,
> > There is some inconsistency in remote wakeup functionality in my
> > custom board. so I want to wakeup the runtime suspended USB host
> > through interrupt. My USB device is connected to the board through USB
> > interface and some gpios. device will give interrupt on processor gpio
> > when it needs attention of USB host. What should i do so that i can
> > wakeup the usb host when i get interrupt from the device.
> 
> Have your gpio interrupt handler call pm_request_resume() for the host
> controller device.
> 
> However, this may not do what you want.  Since the root hub will remain
> suspended, the host controller will go back to low-power immediately
> after it is resumed.  You really need to resume the USB device itself,
> not the host controller.
> 

I think it is the same we echo on > ../power/control, you may need
to request gpio interrupt at your usb class driver, and call pm_runtime_get()
when the gpio interrupt is coming. After the device finishes using
usb, it can call pm_runtme_put through gpio interrupt.

Peter

> > My idea was to apply power management related hooks from the interrupt
> > handler, but I am not getting the clear idea.
> >
> > My main doubt is,
> > Will this mechanism be efficient as remote wakeup functionality?
> 
> That's a hard question to answer without measurements.  But it shouldn't
> matter, because you probably won't get more than one wakeup per second,
> right?
> 
> Alan Stern
> 
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