On Tue, Dec 15, 2015 at 05:34:00PM +0100, Arnd Bergmann wrote: > 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@xxxxxxxxxxxxxx> > > > > > > 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. 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. Thierry
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