On Tuesday 15 December 2015 18:42:36 Thierry Reding wrote:

On Tue, Dec 15, 2015 at 05:34:00PM +0100, Arnd Bergmann wrote:

quoted

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.

I just checked the android lollipop tree, and I could not find a pmc_restart_notify
function, only this file

https://android.googlesource.com/kernel/tegra/+/android-tegra-flounder-3.10-lollipop-release/drivers/htc_debug/stability/reboot_params.c

with the device that stores into RAM. It looks like HTC ported over
a driver that they were already using on some Qualcomm MSM8960 device,
as in 

https://gitlab.com/MaC/android_kernel_htc_msm8960/blob/859977fc723f59a6b707df1d70e80826ee1dccc4/arch/arm/mach-msm/htc/htc_restart_handler.c

On Android marshmallow (Flounder), that file again does not exist, and
I don't see how it's done.

quoted

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.

I wasn't very clear, but the PMC_SCRATCH0 register is used to store the
reset reason. It supports the recovery mode, which I think is really an
Android thing, "bootloader" will typically cause the bootloader not to
boot anything, and "forced-recovery" will go into a recovery mode that
is used to bootstrap the device (usually by uploading a "miniloader"
that initializes RAM, downloads a bootloader for booting or flashing an
operating system, ...).

The write that resets the SoC is to a different register.

So is this scratch register interpreted by some maskrom code, or by code that
can be provided by the OEM?

	Arnd