[0/1] ARM: imx: build suspend-imx6.S with arm instruction set

Commit Message

Max Krummenacher Jan. 11, 2021, 3:17 p.m. UTC

When the kernel is configured to use the Thumb-2 instruction set
"suspend-to-memory" fails to resume while in ARM mode it works as
expected.
(I used imx_v6_v7_defconfig and deselected ARCH_MULTI_V6 and selected
THUMB2_KERNEL)

The system prints what is expected when suspending but an event of a
wakeup source does give no output.

root@colibri-imx6ull:~# echo mem > /sys/power/state

[   58.610809] PM: suspend entry (deep)
[   58.629354] Filesystems sync: 0.014 seconds
[   58.653411] Freezing user space processes ... (elapsed 0.001 seconds) done.
[   58.661941] OOM killer disabled.
[   58.665176] Freezing remaining freezable tasks ... (elapsed 0.001 seconds) done.
[   58.674028] printk: Suspending console(s) (use no_console_suspend to debug)

-> trigger wakeup event, no reaction.

It looks like the CPU resumes unconditionally in ARM instruction mode
and then chokes on the presented Thumb-2 code it should execute on resume.
With the following code change resume succeeds.

I propose however to compile the whole file in ARM mode and have the
linker taking care of the ARM/Thumb-2 switching. This would also keep
the code working if a i.MX CPU variant exists that resumes in the same
mode in which it went to sleep.



Max Krummenacher (1):
  ARM: imx: build suspend-imx6.S with arm instruction set

 arch/arm/mach-imx/suspend-imx6.S | 1 +
 1 file changed, 1 insertion(+)

Patch

--- a/arch/arm/mach-imx/suspend-imx6.S
+++ b/arch/arm/mach-imx/suspend-imx6.S
@@ -287,11 +286,20 @@  rbc_loop:
 	bne	rbc_loop

 	/* Zzz, enter stop mode */
 	wfi
+#ifdef CONFIG_THUMB2_KERNEL
+	/* i.MX CPUs seem to leave stop mode set to ARM instruction set */
+	.arm
+#endif
 	nop
 	nop
 	nop
 	nop
+#ifdef CONFIG_THUMB2_KERNEL
+	/* switch to Thumb2 mode */
+	sub     pc, pc, #3
+	.thumb
+#endif

 	/*