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>
Link: https://lore.kernel.org/r/20220118185746.299832-3-henrik@grimler.se
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
/*
* 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;
/*