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

From: John Stultz <john.stultz@linaro.org>
To: Andy Yan <andy.yan@rock-chips.com>
Cc: "Heiko Stübner" <heiko@sntech.de>,
	"Arnd Bergmann" <arnd@arndb.de>,
	linux@roeck-us.net, "Kumar Gala" <galak@codeaurora.org>,
	"Ian Campbell" <ijc+devicetree@hellion.org.uk>,
	"Rob Herring" <robh+dt@kernel.org>,
	"Catalin Marinas" <catalin.marinas@arm.com>,
	geert+renesas@glider.be, sre@kernel.org,
	"Olof Johansson" <olof@lixom.net>,
	dbaryshkov@gmail.com,
	"Alexandre Belloni" <alexandre.belloni@free-electrons.com>,
	jun.nie@linaro.org, "Paweł Moll" <pawel.moll@arm.com>,
	f.fainelli@gmail.com, "Will Deacon" <will.deacon@arm.com>,
	linux-rockchip@lists.infradead.org, devicetree@vger.kernel.org,
	"Linux PM list" <linux-pm@vger.kernel.org>,
	"Russell King - ARM Linux" <linux@arm.linux.org.uk>,
	"linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>,
	lorenzo.pieralisi@arm.com, moritz.fischer@ettus.com,
	cernekee@gmail.com, lkml <linux-kernel@vger.kernel.org>,
	dwmw2@infradead.org, "Mark Rutland" <mark.rutland@arm.com>,
	maxime.ripard@free-electrons.com,
	"Bjorn Andersson" <bjorn.andersson@linaro.org>
Subject: Re: [PATCH v2 2/4] power: reset: add reboot mode driver
Date: Fri, 15 Jan 2016 12:27:57 -0800	[thread overview]
Message-ID: <CALAqxLVNUG_cVbavXC34sNPv68jbMghti31+PrgQ7mpPngXh6g@mail.gmail.com> (raw)
In-Reply-To: <1452598319-8324-1-git-send-email-andy.yan@rock-chips.com>

On Tue, Jan 12, 2016 at 3:31 AM, Andy Yan <andy.yan@rock-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@rock-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