To enable CPU hotplug the need to provide some boot code at the reset vector and which survives after the kernel has booted without being overwritten. We achieve this by the getting the linker script to place the code in boot.S at address zero. This now means we can delete the code that relocates the secondary CPU pen code to "a location less likely to be overridden".
We then modify the boot protocol slightly to allow hot-plugging of any CPU, including CPU #0, when the system is already booted. This is done by checking if SYS_FLAGS is already set before the normal check for CPU0 and the boot-or-wait decision made.
This patch is based on work by Nicolas Pitre.
Signed-off-by: Nicolas Pitre nico@linaro.org Signed-off-by: Jon Medhurst tixy@linaro.org --- boot.S | 41 ++++++++++++++++++++++++----------------- model.lds.S | 3 ++- 2 files changed, 26 insertions(+), 18 deletions(-)
diff --git a/boot.S b/boot.S index dd453e3..fb56693 100644 --- a/boot.S +++ b/boot.S @@ -12,6 +12,8 @@ .arch_extension virt .text
+ b start @ Must be first instruction for power on reset vector + .macro enter_hyp @ We assume we're entered in Secure Supervisor mode. To @ get to Hyp mode we have to pass through Monitor mode @@ -119,27 +121,32 @@ start: orr r0, r0, r1 mcr p15, 0, r0, c1, c1, 2
- @ Check CPU nr again - mrc p15, 0, r0, c0, c0, 5 @ MPIDR (ARMv7 only) - bfc r0, #24, #8 @ CPU number, taking multicluster into account - cmp r0, #0 @ primary CPU? - beq 2f - - @ - @ Secondary CPUs (following the RealView SMP booting protocol) - @ - enter_hyp - - ldr r1, =fs_start - 0x100 - adr r2, 1f - ldmia r2, {r3 - r7} @ move the code to a location - stmia r1, {r3 - r7} @ less likely to be overridden + /* + * If SYS_FLAGS is already set, this is a warm boot and we blindly + * branch to the indicated address right away, irrespective of the + * CPU we are. + */ #ifdef VEXPRESS ldr r0, =0x1c010030 @ VE SYS_FLAGS register #else ldr r0, =0x10000030 @ RealView SYS_FLAGS register #endif - mov pc, r1 @ branch to the relocated code + ldr r1, [r0] + cmp r1, #0 + beq 1f + enter_hyp + bx r1 +1: + /* + * Otherwise this is a cold boot. In this case it depends if + * we are the primary CPU or not. The primary CPU boots the system + * while the secondaries wait for the primary to set SYS_FLAGS. + */ + mrc p15, 0, r1, c0, c0, 5 + bics r1, #0xff000000 + beq 2f + + enter_hyp 1: #ifdef VEXPRESS wfe @@ -147,7 +154,7 @@ start: ldr r1, [r0] cmp r1, #0 beq 1b - mov pc, r1 @ branch to the given address + bx r1 @ branch to the given address #endif
2: diff --git a/model.lds.S b/model.lds.S index 793df89..f37824e 100644 --- a/model.lds.S +++ b/model.lds.S @@ -27,7 +27,8 @@ STACKTOP = 0xff000000;
SECTIONS { - . = PHYS_OFFSET; + . = 0; + .boot : { boot.o }
. = PHYS_OFFSET + 0x8000 - 0x40;