linux-kernel - Re: [PATCH v3 3/5] soc: rockchip: add reboot notifier driver

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Date:	Tue, 15 Dec 2015 17:31:22 +0100
From:	Thierry Reding <treding@...dia.com>
To:	Arnd Bergmann <arnd@...db.de>
CC:	<linux-arm-kernel@...ts.infradead.org>,
	Andy Yan <andy.yan@...k-chips.com>, <heiko@...ech.de>,
	<linux-kernel@...r.kernel.org>, <mark.rutland@....com>,
	<devicetree@...r.kernel.org>, <khilman@...aro.org>,
	<linux@....linux.org.uk>, <pawel.moll@....com>,
	<ijc+devicetree@...lion.org.uk>, <benchan@...gle.com>,
	<sjg@...omium.org>, <linux-rockchip@...ts.infradead.org>,
	<robh+dt@...nel.org>, <galak@...eaurora.org>, <wxt@...k-chips.com>,
	<john.stultz@...aro.org>
Subject: Re: [PATCH v3 3/5] soc: rockchip: add reboot notifier driver

On Mon, Dec 14, 2015 at 12:39:44PM +0100, Arnd Bergmann wrote:
> On Wednesday 18 November 2015 17:56:22 Andy Yan wrote:
> > rockchip platform have a protocol to pass the kernel reboot
> > mode to bootloader by some special registers when system reboot.
> > By this way the bootloader can take different action according
> > to the different kernel reboot mode, for example, command
> > "reboot loader" will reboot the board to rockusb mode, this is
> > a very convenient way to get the board enter download mode.
> > 
> > Signed-off-by: Andy Yan <andy.yan@...k-chips.com>
> 
> Adding John Stultz to Cc
> 
> I just saw this thread pop up again, and had to think of John's recent
> patch to unify this across platforms.
> 
> John, can you have a look at this driver too, and see how it fits in?
> I think this is yet another variant, using an MMIO register rather than
> RAM (as HTC / NVIDIA does) or SRAM (as Qualcomm does), but otherwise
> it conceptually fits in with what you had.

FWIW, Tegra typically does use an MMIO register as well. See
drivers/soc/tegra/pmc.c:tegra_pmc_restart_notify(). I don't know what
HTC does, but if it's writing somewhere in RAM it isn't using the
standard way of resetting the SoC. There's early boot ROM code which I
think evaluates the PMC_SCRATCH0 register on Tegra to determine which
mode to boot into. That's before even any firmware gets the chance of
doing anything.

Thierry

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