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

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Date:	Wed, 5 Mar 2014 11:05:34 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Jagdish Gedia <jvgediya@...il.com>
cc:	linux-usb@...r.kernel.org, <linux-kernel@...r.kernel.org>
Subject: Re: USB remote wakeup through gpio interrupt

On Wed, 5 Mar 2014, Jagdish Gedia wrote:

> 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.

> 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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