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

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Date:	Tue, 15 Dec 2015 17:34 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Thierry Reding <treding@...dia.com>
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 Tuesday 15 December 2015 17:31:22 Thierry Reding wrote:
> 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.

HTC apparently uses a separate RAM area to pass the reboot reason,
and they have a driver to store that, which is separate from the
driver that they use for actually rebooting the machine.

	Arnd
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