On Fri, 6 Jun 2014, Doug Anderson wrote:
> On exynos mcpm systems the firmware is hardcoded to jump to an address
> in SRAM (0x02073000) when secondary CPUs come up. By default the
> firmware puts a bunch of code at that location. That code expects the
> kernel to fill in a few slots with addresses that it uses to jump back
> to the kernel's entry point for secondary CPUs.
>
> Originally (on prerelease hardware) this firmware code contained a
> bunch of workarounds to deal with boot ROM bugs. However on all
> shipped hardware we simply use this code to redirect to a kernel
> function for bringing up the CPUs.
>
> Let's stop relying on the code provided by the bootloader and just
> plumb in our own (simple) code jump to the kernel. This has the nice
> benefit of fixing problems due to the fact that older bootloaders
> (like the one shipped on the Samsung Chromebook 2) might have put
> slightly different code into this location.
>
> Once suspend/resume is implemented for systems using exynos-mcpm we'll
> need to make sure we reinstall our fixed up code after resume. ...but
> that's not anything new since IRAM (and thus the address of the
> mcpm_entry_point) is lost across suspend/resume anyway.
>
> Signed-off-by: Doug Anderson <dianders@xxxxxxxxxxxx>
> ---
> arch/arm/mach-exynos/mcpm-exynos.c | 10 ++++++----
> 1 file changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/arch/arm/mach-exynos/mcpm-exynos.c b/arch/arm/mach-exynos/mcpm-exynos.c
> index 0498d0b..3a7fad0 100644
> --- a/arch/arm/mach-exynos/mcpm-exynos.c
> +++ b/arch/arm/mach-exynos/mcpm-exynos.c
> @@ -343,11 +343,13 @@ static int __init exynos_mcpm_init(void)
> pr_info("Exynos MCPM support installed\n");
>
> /*
> - * Future entries into the kernel can now go
> - * through the cluster entry vectors.
> + * U-Boot SPL is hardcoded to jump to the start of ns_sram_base_addr
> + * as part of secondary_cpu_start(). Let's redirect it to the
> + * mcpm_entry_point().
> */
> - __raw_writel(virt_to_phys(mcpm_entry_point),
> - ns_sram_base_addr + MCPM_BOOT_ADDR_OFFSET);
> + __raw_writel(0xe59f0000, ns_sram_base_addr); /* ldr r0, [pc, #0] */
> + __raw_writel(0xe12fff10, ns_sram_base_addr + 4); /* bx r0 */
> + __raw_writel(virt_to_phys(mcpm_entry_point), ns_sram_base_addr + 8);
Is this valid for all exynos systems, or is this particular to
Chromebooks?
If this is all that is needed to solve the problem being discussed in
the other thread I have absolutely no issue with such a workaround going
into mainline.
Nicolas
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