linux-kernel - RE: [PATCH v2 4/4] da850-evm: add baseboard UI expander buttons, switches and LEDs

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Message-ID: <B85A65D85D7EB246BE421B3FB0FBB593024793124F@dbde02.ent.ti.com>
Date:	Tue, 23 Nov 2010 18:12:38 +0530
From:	"Nori, Sekhar" <nsekhar@...com>
To:	Ben Gardiner <bengardiner@...ometrics.ca>
CC:	Kevin Hilman <khilman@...prootsystems.com>,
	"davinci-linux-open-source@...ux.davincidsp.com" 
	<davinci-linux-open-source@...ux.davincidsp.com>,
	"linux-input@...r.kernel.org" <linux-input@...r.kernel.org>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	"Govindarajan, Sriramakrishnan" <srk@...com>,
	Paul Mundt <lethal@...ux-sh.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Alexander Clouter <alex@...riz.org.uk>,
	Chris Cordahi <christophercordahi@...ometrics.ca>
Subject: RE: [PATCH v2 4/4] da850-evm: add baseboard UI expander buttons,
 switches and LEDs

Hi Ben,

On Mon, Nov 22, 2010 at 19:45:46, Ben Gardiner wrote:
> Hi Sekhar,
>
> On Mon, Nov 22, 2010 at 7:00 AM, Nori, Sekhar <nsekhar@...com> wrote:
> > Thanks for the explanation. I should have probably asked
> > earlier, why do we need to prevent sysfs access of
> > deep sleep enable and sw reset pins? We don't seem to be
> > using them in the kernel either.
>
> You're welcome.
>
> I was assuming that those pins were not exported as gpio pins on
> purpose; I was taking the prudent approach to prevent haphazard
> toggling of sw_rst and deep_sleep_en from userspace. sw_rst because it
> could initiate a reset of the cpu when toggled and deep_sleep_en
> because it can override the behaviour of davinci_pm_enter().
>
> I'm not sure how they would be used by existing kernel classes either.
> The sw_rst pin could be used for reset but since it is on the other
> end of an i2c bus and there is an existing implementation of reset
> using the on chip watchdog I don't think it would be benficial to
> switch. Deep_sleep_en could override the behaviour in
> davinci_pm_enter() -- _maybe_ (I don't really know) it could be used
> as a hardware-assisted suspend-blocker? But I totally guessing here.

My preference would be to leave these pins as is
(don't call a gpio_request() on them) till someone
comes up with a use case for them. From what you
described, sysfs access cannot happen "accidently"
so someone accessing these pins from sysfs surely
knows what he is doing.

Thanks,
Sekhar

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