linux-kernel - Re: [PATCH 1/3] ARM: dts: omap5-board-common: enable rtc and charging of backup battery

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Message-ID: <56977211.8070206@ti.com>
Date:	Thu, 14 Jan 2016 15:31:53 +0530
From:	Keerthy <a0393675@...com>
To:	Nishanth Menon <menon.nishanth@...il.com>,
	Tony Lindgren <tony@...mide.com>, Nishanth Menon <nm@...com>
CC:	"H. Nikolaus Schaller" <hns@...delico.com>,
	Grygorii Strashko <grygorii.strashko@...com>,
	Laxman Dewangan <ldewangan@...dia.com>,
	Benoît Cousson <bcousson@...libre.com>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Russell King <linux@....linux.org.uk>,
	linux-omap <linux-omap@...r.kernel.org>,
	<devicetree@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
	Marek Belisko <marek@...delico.com>,
	Gražvydas Ignotas <notasas@...il.com>,
	Keerthy <j-keerthy@...com>
Subject: Re: [PATCH 1/3] ARM: dts: omap5-board-common: enable rtc and charging
 of backup battery



On Thursday 14 January 2016 04:02 AM, Nishanth Menon wrote:
> On 01/13/2016 01:40 PM, Tony Lindgren wrote:
>
>> Anyways, considering what's been discussed, after the minimal RTC fix
>> we could also add code to allow the TWL driver optionally configure the
>> GPIO. This way the TWL driver could also check the GPIO state in case
>> some out-of-our-control mystery software goes tweak the msecure pin
>> state.
>
> I dont even know how that will work:
> If you are using MSECURE as it is intended to be, then you'd mux it to
> msecure, which means that GPIO read is just a waste of time - you dont
> even mux it to external world. Now, some SoCs like DRA7 has input lines
> always connected. even assuming this is for such a case:
> a) when you are running linux, you are already in nonsecure - it needs
> no read of MSECURE GPIO to figure that out.
> b)  when you are in secure world, Linux wont be running either.
>
> Reading from GPIO is just misguided in my opinion. firewalls are not
> reconfigured, and muxes are usually done a single time.
>
>   Or the RTC driver could just check that the bits really change
>> after= writing them. Then we would at least know things are not working
>> right for the TWL related RTC drivers.
>
> that is reasonable to check, but just a overhead - anyways, just
> isolated to palmas-rtc.. fail reason maynot always be issues with
> MSECURE mux.. it could be very well be 32k clk fail etc.. but yeah -
> that might give a hint that there is an issue..
>

IIRC without configuring the mux mode of gpio234 to msecure mode we were 
unable to write to the rtc registers. Hence configured it one time at boot.