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

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Message-ID: <CAE1zotJ8RcSing2cQWPFzHoEiH1FH1-NsYZrShuQ=hVEwextug@mail.gmail.com>
Date:	Thu, 8 Jan 2015 02:16:15 +1300
From:	Octavian Purdila <octavian.purdila@...el.com>
To:	Johan Hovold <johan@...nel.org>
Cc:	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 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. 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.
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