[PATCH v3 2/3] ARM: exynos: only do SMC_CMD_CPU1BOOT call on Exynos4

Henrik Grimler
2022-01-16T16:51:35Z

On Exynos5 the call is simply ignored by most variants of the
trustzone firmware. However, on some devices it instead causes the
device to hang, so let's avoid the call for the SoCs where it should
not be needed.

To see that the call is ignored, we can look into sboot/tzsw. On most
of the Exynos{4,5} devices the part of sboot/tzsw that seem to handle
the secure monitor calls is quite easy to recognise, the SMC number is
compared to known ones, and if equal it branches to the relevant
function. In assembly this looks something like:

;-- handle_smc:
0x00000514 650070e3 cmn r0, 0x65
0x00000518 0a00000a beq loc.smc_cmd_reg
0x0000051c 010070e3 cmn r0, 1
0x00000520 6c00000a beq loc.smc_cmd_init
0x00000524 020070e3 cmn r0, 2
0x00000528 6b00000a beq loc.smc_cmd_info
0x0000052c 030070e3 cmn r0, 3
0x00000530 6e00000a beq loc.smc_cmd_sleep
0x00000534 060070e3 cmn r0, 6
0x00000538 ae00000a beq loc.smc_cmd_save_state
0x0000053c 070070e3 cmn r0, 7
0x00000540 b400000a beq loc.smc_cmd_standby
0x00000544 2b01001a bne loc.smc_return_minus1

where above example is from exynos5420-arndale-octa. As can be seen
the case where r0 is 4 (i.e. SMC_CMD_CPU1BOOT) is not handled. The
annotations are taken from github.com/hsnaves/exynos5410-firmware,
where a large part of the exynos5410 trustzone firmware has been
reverse-engineered.

Signed-off-by: Henrik Grimler <henrik@grimler.se>
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
---
Sent previously as RFC
---
arch/arm/mach-exynos/firmware.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/arm/mach-exynos/firmware.c b/arch/arm/mach-exynos/firmware.c
index 2eaf2dbb8e81..2da5b60b59e2 100644
--- a/arch/arm/mach-exynos/firmware.c
+++ b/arch/arm/mach-exynos/firmware.c
@@ -60,8 +60,10 @@ static int exynos_cpu_boot(int cpu)
/*
* Exynos3250 doesn't need to send smc command for secondary CPU boot
* because Exynos3250 removes WFE in secure mode.
+ *
+ * On Exynos5 devices the call is ignored by trustzone firmware.
*/
- if (soc_is_exynos3250())
+ if (!soc_is_exynos4210() && !soc_is_exynos4412())
return 0;

/*
--
2.34.1