linux-kernel - Re: [PATCH] gpio: pcf857x: restore the initial line state of all pcf lines

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Message-ID: <CACRpkdaFXvqbo84BqBVJzoBqdejwauxhZDr+x4HgWbXehOqViw@mail.gmail.com>
Date:	Wed, 25 Mar 2015 16:28:29 +0100
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Kishon Vijay Abraham I <kishon@...com>
Cc:	Nishanth Menon <nm@...com>, Alexandre Courbot <gnurou@...il.com>,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Sekhar Nori <nsekhar@...com>,
	Linux-OMAP <linux-omap@...r.kernel.org>,
	"linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
	Benoit Parrot <bparrot@...com>
Subject: Re: [PATCH] gpio: pcf857x: restore the initial line state of all pcf lines

On Wed, Mar 18, 2015 at 2:21 PM, Kishon Vijay Abraham I <kishon@...com> wrote:
>[Me]
>> Specify exactly what stuff may happen after the reboot notifier.
>
> okay, it's assumed the device may be used (active) till the shutdown handler
> of that particular device is called.
>
> In this particular case we are restoring the initial line state of all pcf
> lines even though we don't know if the devices connected to it are still
> being active, which might cause a contention as explained by NM [1]

OK I understand this, just that I want to know if it is a practical problem,
i.e. do you run into it? Does the system lock up?

> If the reboot notifier gets invoked after the shutdown handler then we could
> be sure that restoring the initial line state of the pcf lines wouldn't
> affect the devices connected to it.

OK so does it?

ftrace is your friend.

Yours,
Linus Walleij
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