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. Thierry
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