Re: [PATCH v2] ARM: EXYNOS: mcpm: Don't rely on firmware's secondary_cpu_start
From: Nicolas Pitre
Date: Fri Jun 06 2014 - 21:34:12 EST
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>
Acked-by: Nicolas Pitre <nico@xxxxxxxxxx>
> ---
> Changes in v2:
> - Removed #define
>
> arch/arm/mach-exynos/mcpm-exynos.c | 11 ++++++-----
> 1 file changed, 6 insertions(+), 5 deletions(-)
>
> diff --git a/arch/arm/mach-exynos/mcpm-exynos.c b/arch/arm/mach-exynos/mcpm-exynos.c
> index 0498d0b..ace0ed6 100644
> --- a/arch/arm/mach-exynos/mcpm-exynos.c
> +++ b/arch/arm/mach-exynos/mcpm-exynos.c
> @@ -25,7 +25,6 @@
>
> #define EXYNOS5420_CPUS_PER_CLUSTER 4
> #define EXYNOS5420_NR_CLUSTERS 2
> -#define MCPM_BOOT_ADDR_OFFSET 0x1c
>
> /*
> * The common v7_exit_coherency_flush API could not be used because of the
> @@ -343,11 +342,13 @@ 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);
>
> iounmap(ns_sram_base_addr);
>
> --
> 2.0.0.526.g5318336
>
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