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

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Message-ID: <20140507220049.GC7047@lukather>
Date:	Wed, 7 May 2014 17:00:49 -0500
From:	Maxime Ripard <maxime.ripard@...e-electrons.com>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Emilio Lopez <emilio@...pez.com.ar>,
	Mike Turquette <mturquette@...aro.org>, kishon@...com,
	hdegoede@...hat.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

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?

Thanks,
Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

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