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

[Thierry Reding <treding-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>]

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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-TNX95d0MmH7DzftRWevZcw@public.gmane.org>
> 
> 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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