Re: [PATCH 16/16] ARM: OMAP: omap4panda: Power down the USB PHY and ETH when not in use

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On 11/21/2012 04:52 PM, Alan Stern wrote:
> On Wed, 21 Nov 2012, Felipe Balbi wrote:
> 
>> On Thu, Nov 15, 2012 at 04:34:14PM +0200, Roger Quadros wrote:
>>> From: Andy Green <andy.green@xxxxxxxxxx>
>>>
>>> This patch changes the management of the two GPIO for
>>> "hub reset" (actually controls enable of ULPI PHY and hub reset) and
>>> "hub power" (controls power to hub + eth).
>>
>> looks like this should be done by the hub driver. Alan, what would you
>> say ? Should the hub driver know how to power itself up ?
> 
> Not knowing the context, I'm a little confused.  What is this hub 
> you're talking about?  Is it a separate USB hub incorporated into the 
> IP (like Intel's "rate-matching" hubs in their later chipsets)?  Or is 
> it the root hub?
> 

This is actually a USB HUB + Ethernet combo chip (LAN9514) that is hard
wired on the panda board with its Power and Reset pins controlled by 2
GPIOs from the OMAP SoC.

When powered, this chip can consume significant power (~0.7 W) because
of the (integrated Ethernet even when suspended. I suppose the ethernet
driver SMSC95XX) doesn't put it into a low enough power state on suspend.

It doesn't make sense to power the chip when USB is not required on the
whole (e.g. ehci_hcd module is not loaded). This is what this patch is
trying to fix.

cheers,
-roger
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