[BOOT-WRAPPER 01/11] Always enter AArch32 kernels in ARM mode

[Mark Rutland]

Currnetly we try to support entering AArch32 kernels, but this is
unnecessary, and the code is never exercised.

Per Linux's Documentation/arch/arm/booting.txt, AArch32 kernels
supported by the AArch64 boot-wrapper should always be entered in ARM
mode:

| The boot loader is expected to call the kernel image by jumping
| directly to the first instruction of the kernel image.
|
| On CPUs supporting the ARM instruction set, the entry must be
| made in ARM state, even for a Thumb-2 kernel.
|
| On CPUs supporting only the Thumb instruction set such as
| Cortex-M class CPUs, the entry must be made in Thumb state.

Additionally, the kernel__start symbol that we use as the kernel
entrypoint is always PHYS_OFFSET + KERNEL_OFFSET, which doesn't take
into account any ARM/Thumb distinction in the AArch32 kernel image, and
hence we'll never try to set the Thumb bit in the SPSR.

Remove the redundant code.

Signed-off-by: Mark Rutland <mark.rutland at arm.com>
Cc: Akos Denke <akos.denke at arm.com>
Cc: Andre Przywara <andre.przywara at arm.com>
Cc: Luca Fancellu <luca.fancellu at arm.com>
Cc: Marc Zyngier <maz at kernel.org>
---
 arch/aarch32/boot.S | 4 ----
 arch/aarch64/boot.S | 7 -------
 2 files changed, 11 deletions(-)

diff --git a/arch/aarch32/boot.S b/arch/aarch32/boot.S
index 4d16c9c..5c2a183 100644
--- a/arch/aarch32/boot.S
+++ b/arch/aarch32/boot.S
@@ -105,10 +105,6 @@ ASM_FUNC(jump_kernel)
 	bxeq	lr				@ no EL3
 
 	ldr	r4, =SPSR_KERNEL
-	/* Return in thumb2 mode when bit 0 of address is 1 */
-	tst	lr, #1
-	orrne	r4, #PSR_T
-
 	msr	spsr_cxf, r4
 	movs	pc, lr
 
diff --git a/arch/aarch64/boot.S b/arch/aarch64/boot.S
index da5fa65..b889137 100644
--- a/arch/aarch64/boot.S
+++ b/arch/aarch64/boot.S
@@ -136,13 +136,6 @@ ASM_FUNC(jump_kernel)
 	br	x19			// No EL3
 
 1:	mov	x4, #SPSR_KERNEL
-
-	/*
-	 * If bit 0 of the kernel address is set, we're entering in AArch32
-	 * thumb mode. Set SPSR.T accordingly.
-	 */
-	bfi	x4, x19, #5, #1
-
 	msr	elr_el3, x19
 	msr	spsr_el3, x4
 	eret
-- 
2.30.2