[PATCH] ARM: EXYNOS: mcpm: Don't rely on firmware's secondary_cpu_start

[Doug Anderson]

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 at chromium.org>
---
 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);
 
 	iounmap(ns_sram_base_addr);
 
-- 
2.0.0.526.g5318336