diff options
Diffstat (limited to 'target/linux/bcm27xx/patches-5.4/950-0927-ARM-proc-v7-Force-misalignment-of-early-stmia.patch')
| -rw-r--r-- | target/linux/bcm27xx/patches-5.4/950-0927-ARM-proc-v7-Force-misalignment-of-early-stmia.patch | 60 |
1 files changed, 60 insertions, 0 deletions
diff --git a/target/linux/bcm27xx/patches-5.4/950-0927-ARM-proc-v7-Force-misalignment-of-early-stmia.patch b/target/linux/bcm27xx/patches-5.4/950-0927-ARM-proc-v7-Force-misalignment-of-early-stmia.patch new file mode 100644 index 0000000000..158ff69bff --- /dev/null +++ b/target/linux/bcm27xx/patches-5.4/950-0927-ARM-proc-v7-Force-misalignment-of-early-stmia.patch @@ -0,0 +1,60 @@ +From 965cce6b1c6acc25d7cfd29ccf95c8ebbf1d7f57 Mon Sep 17 00:00:00 2001 +From: Phil Elwell <phil@raspberrypi.com> +Date: Wed, 29 Jul 2020 13:47:55 +0100 +Subject: [PATCH] ARM: proc-v7: Force misalignment of early stmia + +In an attempt to prevent the problem of CPUn not starting, explicitly +misalign the scratch space used to save registers acros the cache +invalidation. + +Notes: +At this stage in the boot process the core is running with its cache +disabled. Before enabling the cache its contents must be explicitly +invalidated, a process that requires quite a few registers that the +caller must preserve. Evidence suggests that something is writing a +block of zeroes over that space at a time when all other cores should +be idle, possibly some kind of write-combiner, and the misalignment is +designed to disrupt any write-coalescing. + +In truth, I don't understand why this patch works, and when the failure +is so random it is hard to be certain that this isn't just rolling the +dice again. One interesting test would be to change the "addeq r12, #4"s +to "addeq r12, #0"s determine see if the offset itself is significant or +just the additional code. + +See: https://github.com/Hexxeh/rpi-firmware/issues/232 + +Signed-off-by: Phil Elwell <phil@raspberrypi.com> +--- + arch/arm/mm/proc-v7.S | 6 +++++- + 1 file changed, 5 insertions(+), 1 deletion(-) + +--- a/arch/arm/mm/proc-v7.S ++++ b/arch/arm/mm/proc-v7.S +@@ -287,6 +287,8 @@ __v7_ca17mp_setup: + mov r10, #0 + 1: adr r0, __v7_setup_stack_ptr + ldr r12, [r0] ++ tst r12, #0x1f ++ addeq r12, r12, #4 + add r12, r12, r0 @ the local stack + stmia r12, {r1-r6, lr} @ v7_invalidate_l1 touches r0-r6 + bl v7_invalidate_l1 +@@ -474,6 +476,8 @@ __v7_setup: + adr r0, __v7_setup_stack_ptr + ldr r12, [r0] + add r12, r12, r0 @ the local stack ++ tst r12, #0x1f ++ addeq r12, r12, #4 + stmia r12, {r1-r6, lr} @ v7_invalidate_l1 touches r0-r6 + bl v7_invalidate_l1 + ldmia r12, {r1-r6, lr} +@@ -557,7 +561,7 @@ ENDPROC(__v7_setup) + .bss + .align 2 + __v7_setup_stack: +- .space 4 * 7 @ 7 registers ++ .space 4 * 8 @ 7 registers + 1 spare + + __INITDATA + |