linux-kernel - Re: [RFC][PATCH] misc: Introduce reboot

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Date:	Thu, 10 Dec 2015 11:20:06 +0200
From:	Tomas Winkler <tomasw@...il.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	John Stultz <john.stultz@...aro.org>,
	Bjorn Andersson <bjorn.andersson@...ymobile.com>,
	lkml <linux-kernel@...r.kernel.org>,
	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>,
	Vinay Simha BN <simhavcs@...il.com>,
	Haojian Zhuang <haojian.zhuang@...aro.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Android Kernel Team <kernel-team@...roid.com>,
	Andy Gross <agross@...eaurora.org>,
	"linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>
Subject: Re: [RFC][PATCH] misc: Introduce reboot_reason driver

On Thu, Dec 10, 2015 at 11:05 AM, Arnd Bergmann <arnd@...db.de> wrote:
> On Wednesday 09 December 2015 17:32:02 John Stultz wrote:
>> On Tue, Dec 8, 2015 at 2:07 PM, Bjorn Andersson
>> <bjorn.andersson@...ymobile.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@...3f65c {
>> >> +                     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

Intel uses EFI variables for that on  some AOS platforms. There is a
need for persistent storage abstraction and generalize the reboot
reasons strings.
Second, I wonder why this is submitted under drivers/misc when it
doesn't bind the misc API.

Thanks
Tomas
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