Am Dienstag, 15. Dezember 2015, 17:34:00 schrieb Arnd Bergmann:

On Tuesday 15 December 2015 17:31:22 Thierry Reding wrote:

quoted

On Mon, Dec 14, 2015 at 12:39:44PM +0100, Arnd Bergmann wrote:

quoted

On Wednesday 18 November 2015 17:56:22 Andy Yan wrote:

quoted

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.

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.

same on Rockchip. The general restart handling doesn't care about any reason, 
it is merely an agreement between kernel and bootloader to store a reason 
value in some reboot-safe register of the soc.


Heiko