linux-kernel - Re: [PATCH v2 4/4] mfd: dln2: add suspend/resume functionality

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Message-ID: <20150107142605.GG22905@localhost>
Date:	Wed, 7 Jan 2015 15:26:05 +0100
From:	Johan Hovold <johan@...nel.org>
To:	Octavian Purdila <octavian.purdila@...el.com>
Cc:	Johan Hovold <johan@...nel.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	Lee Jones <lee.jones@...aro.org>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	lkml <linux-kernel@...r.kernel.org>,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>
Subject: Re: [PATCH v2 4/4] mfd: dln2: add suspend/resume functionality

On Thu, Jan 08, 2015 at 02:16:15AM +1300, Octavian Purdila wrote:
> On Wed, Jan 7, 2015 at 11:26 PM, Johan Hovold <johan@...nel.org> wrote:
> > On Tue, Dec 16, 2014 at 05:57:15PM +0200, Octavian Purdila wrote:
> >> Without suspend/resume functionality in the USB driver the USB core
> >> will disconnect and reconnect the DLN2 port and because the GPIO
> >> framework does not yet support removal of an in-use controller a
> >> suspend/resume operation will result in a crash.
> >>
> >> This patch provides suspend and resume functions for the DLN2 driver
> >> so that the above scenario is avoided.
> >>
> >> Signed-off-by: Octavian Purdila <octavian.purdila@...el.com>
> >
> > This patch looks good now, but how did you say this device was powered?
> >
> > If powered by vbus you cannot assume that the device maintains it's
> > state over a suspend cycle, something which would complicate matters
> > quite a bit...
> 
> Yes, the device is powered by VBUS. During my tests, depending on the
> host and USB port, VBUS is sometimes preserved - and this is the case
> this patch addresses, and sometimes is not, but in that case because
> no reset_resume routine is implemented the resume path will go through
> the disconnect/reconnect process.

Yes, it depends on the host controller and I believe the common case is
to drop VBUS.

> This second case is not addressed by
> the patch, as I think in this second case fixing the GPIO framework to
> support the removal of an in-use device is the best way to go.

I agree.

But please do mention that this case is not handled in the commit
message.

Thanks,
Johan
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