linux-kernel - Re: [PATCH v2 2/4] power: reset: add reboot mode driver

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Message-ID: <CALAqxLVNUG_cVbavXC34sNPv68jbMghti31+PrgQ7mpPngXh6g@mail.gmail.com>
Date:	Fri, 15 Jan 2016 12:27:57 -0800
From:	John Stultz <john.stultz@...aro.org>
To:	Andy Yan <andy.yan@...k-chips.com>
Cc:	Heiko Stübner <heiko@...ech.de>,
	Arnd Bergmann <arnd@...db.de>, linux@...ck-us.net,
	Kumar Gala <galak@...eaurora.org>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Rob Herring <robh+dt@...nel.org>,
	Catalin Marinas <catalin.marinas@....com>,
	geert+renesas@...der.be, sre@...nel.org,
	Olof Johansson <olof@...om.net>, dbaryshkov@...il.com,
	Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
	jun.nie@...aro.org,
	Paweł Moll <pawel.moll@....com>,
	f.fainelli@...il.com, Will Deacon <will.deacon@....com>,
	linux-rockchip@...ts.infradead.org, devicetree@...r.kernel.org,
	Linux PM list <linux-pm@...r.kernel.org>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>, lorenzo.pieralisi@....com,
	moritz.fischer@...us.com, cernekee@...il.com,
	lkml <linux-kernel@...r.kernel.org>, dwmw2@...radead.org,
	Mark Rutland <mark.rutland@....com>,
	maxime.ripard@...e-electrons.com,
	Bjorn Andersson <bjorn.andersson@...aro.org>
Subject: Re: [PATCH v2 2/4] power: reset: add reboot mode driver

On Tue, Jan 12, 2016 at 3:31 AM, Andy Yan <andy.yan@...k-chips.com> wrote:
> This driver parse the reboot commands like "reboot loader"
> and "reboot recovery" to get a boot mode described in the
> device tree , then call the write interfae to store the boot
> mode in some persistent storage  like special register or ram,
> which can be read by the bootloader after system reboot, then
> the bootloader can take different action according to the mode
> stored.
>
> This is commonly used on Android based devices, which in order
> to reboot the device into fastboot or recovery mode.
>
> Signed-off-by: Andy Yan <andy.yan@...k-chips.com>

Hey Andy!
  Thanks for keeping this work going! I've just successfully reworked
my Nexus7 tree to use your implementation (using the syscon version,
setting up a syscon for IMEM as Bjorn had requested earlier).

All is working well so far!

The one thing I was working on supporting with my own version that
seems to be missing here are for devices that use string based codes,
rather then magic numbers.

This was mostly a theoretical issue. I think the Galaxy Nexus used it,
and when I was looking at some of the HTC devices, they support a text
based reason along with the magic code, but at least in some
implementations the text mode isn't used, so I suspect there its just
for extra debugging.  So this may not be critical to solve until
someone tries to add support for such a device.

Anyway, I'm going to look at porting this to the HiKey board next
(which just uses reserved ram, not syscon), so I'll try to do a an
SRAM driver implementaiton to see how that goes.

thanks!
-john