[RFC PATCH v3 3/8] arm64: head.S : Change register usage

Suzuki K. Poulose
2015-12-09T10:00:22Z

The stack information for a secondary CPU (struct secondary_data)
is passed on in x21 before the MMU is turned on. The boot CPU uses
x21 to store the FDT pointer. In a common code shared by these
CPUs, it gets difficult to use the information. So, we use
x22 for passing the secondary_data and initialise it with NULL
for the booting CPU for consistency. This will be used in a following
patch.

Cc: Will Deacon <will.deacon@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Suzuki K. Poulose <suzuki.poulose@arm.com>
---
arch/arm64/kernel/head.S | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index 23cfc08..b225d34 100644
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S
@@ -221,6 +221,7 @@ ENTRY(stext)
*/
ldr x27, =__mmap_switched // address to jump to after
// MMU has been enabled
+ mov x22, 0 // &secondary_data for Boot CPU
adr_l lr, __enable_mmu // return (PIC) address
b __cpu_setup // initialise processor
ENDPROC(stext)
@@ -598,13 +599,13 @@ ENTRY(secondary_startup)
adrp x26, swapper_pg_dir
bl __cpu_setup // initialise processor

- ldr x21, =secondary_data
+ ldr x22, =secondary_data
ldr x27, =__secondary_switched // address to jump to after enabling the MMU
b __enable_mmu
ENDPROC(secondary_startup)

ENTRY(__secondary_switched)
- ldr x0, [x21] // get secondary_data.stack
+ ldr x0, [x22] // get secondary_data.stack
mov sp, x0
mov x29, #0
b secondary_start_kernel
--
1.7.9.5