From: Arnd Bergmann <arnd@arndb.de>
To: John Stultz <john.stultz@linaro.org>
Cc: Bjorn Andersson <bjorn.andersson@sonymobile.com>,
        lkml <linux-kernel@vger.kernel.org>, Rob Herring <robh+dt@kernel.org>,
        Pawel Moll <pawel.moll@arm.com>, Mark Rutland <mark.rutland@arm.com>,
        Ian Campbell <ijc+devicetree@hellion.org.uk>,
        Kumar Gala <galak@codeaurora.org>, Vinay Simha BN <simhavcs@gmail.com>,
        Haojian Zhuang <haojian.zhuang@linaro.org>,
        "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
        Android Kernel Team <kernel-team@android.com>,
        Andy Gross <agross@codeaurora.org>,
        "linux-arm-msm@vger.kernel.org" <linux-arm-msm@vger.kernel.org>
Subject: Re: [RFC][PATCH] misc: Introduce reboot_reason driver
Date: Thu, 10 Dec 2015 10:05:33 +0100
Message-ID: <27901180.P9mpafrzx5@wuerfel>
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On Wednesday 09 December 2015 17:32:02 John Stultz wrote:
> On Tue, Dec 8, 2015 at 2:07 PM, Bjorn Andersson
> <bjorn.andersson@sonymobile.com> wrote:
> > On Tue 08 Dec 13:29 PST 2015, John Stultz wrote:
> >> diff --git a/arch/arm/boot/dts/qcom-apq8064-nexus7-flo.dts b/arch/arm/boot/dts/qcom-apq8064-nexus7-flo.dts
> >> index 5183d18..ee5dcb7 100644
> >> --- a/arch/arm/boot/dts/qcom-apq8064-nexus7-flo.dts
> >> +++ b/arch/arm/boot/dts/qcom-apq8064-nexus7-flo.dts
> >> @@ -282,6 +282,15 @@
> >>                       };
> >>               };
> >>
> >> +             reboot_reason: reboot_reason@2a03f65c {
> >> +                     compatible              = "reboot_reason";
> >> +                     reg                     = <0x2A03F65C 0x4>;
> >> +                     reason,none             = <0x77665501>;
> >> +                     reason,bootloader       = <0x77665500>;
> >> +                     reason,recovery         = <0x77665502>;
> >> +                     reason,oem              = <0x6f656d00>;
> >> +             };
> >> +
> >
> > This address refers to IMEM, which is shared with a number of other
> > uses. So I think we should have a simple-mfd (and syscon) with this
> > within.
> 
> So talking with Arnd some more it looked like IMEM was really just
> SRAM. Is that not the case, or is there something else special about
> it?  Does it really need simple-mfd and syscon? I'm still fuzzy on how
> to use those for this.

If it's SRAM, we should use the SRAM binding and not make it a syscon
device. What we can have however, is a mostly somewhat reboot-reason
driver that is able to access an SRAM device or something else,
depending on what the platform and/or bootloader has.

HTC's Nexus 9 apparently uses a section of normal RAM for communication
between bootloader and kernel, so we'd also need a way to hook into
a driver for that.

	Arnd
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