linux-kernel - Re: [PATCH 4/7] usb: ehci-platform: add optional reset controller retrieval

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Date:	Thu, 08 May 2014 09:29:16 +0200
From:	Hans de Goede <hdegoede@...hat.com>
To:	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	Alan Stern <stern@...land.harvard.edu>
CC:	Emilio Lopez <emilio@...pez.com.ar>,
	Mike Turquette <mturquette@...aro.org>, kishon@...com,
	Boris Brezillon <boris@...e-electrons.com>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-usb@...r.kernel.org, kevin.z.m.zh@...il.com,
	sunny@...winnertech.com, shuge@...winnertech.com,
	zhuzhenhua@...winnertech.com, linux-sunxi@...glegroups.com,
	Boris BREZILLON <boris.brezillon@...e-electrons.com>
Subject: Re: [PATCH 4/7] usb: ehci-platform: add optional reset controller
 retrieval

Hi,

On 05/08/2014 12:00 AM, Maxime Ripard wrote:
> On Wed, May 07, 2014 at 10:25:55AM -0400, Alan Stern wrote:
>> On Tue, 6 May 2014, Maxime Ripard wrote:
>>
>>> From: Boris BREZILLON <boris.brezillon@...e-electrons.com>
>>>
>>> On the Allwinner's A31 SoC the reset line connected to the EHCI IP has to
>>> be deasserted for the EHCI block to be usable.
>>>
>>> Add support for an optional reset controller that will be deasserted on
>>> power off and asserted on power on.
>>>
>>> Signed-off-by: Boris BREZILLON <boris.brezillon@...e-electrons.com>
>>> Signed-off-by: Maxime Ripard <maxime.ripard@...e-electrons.com>
>>
>> Is this really a _reset_ line?  That is, when you assert the reset 
>> line, does it actually reset the EHCI controller, or does it merely 
>> leave the controller in a partially powered-down state?
> 
> It actually resets the whole controller.
> 
>> The difference is important.  During suspend, the controller is
>> supposed to remember the state of the port connections as well as other
>> settings.  If it doesn't, the controller and all attached USB devices
>> will have to be reinitialized every time the controller resumes, which
>> will increase the latency.
> 
> So you're saying that we should move this to the probe then?

Yes.

Regards,

Hans
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