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    SubjectRe: [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@rock-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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