Re: [PATCH] arm: mach-k3: am625: Unlock MMR registers again

[Daniel Schultz <d.schultz@phytec.de>]

Hi Alexander,

On 8/21/25 18:21, Sverdlin, Alexander wrote:
> Dear Daniel, TI team,
>
> On Fri, 2025-08-15 at 09:02 -0700, Daniel Schultz wrote:
>> The watchdog requires to have the MCU ESM error source enabled to
>> trigger a system reboot. When booting HS-SE (security enforced)
>> devices, the MMR registers are locked again and all write commands
>> are simply ignored.
>>
>> Unlock the MMR registers again to successfully enable the MCU ESM
>> source.
> I'm just curious, could you please elaborate a bit, where the registers
> are being locked again if they are being unlocked by ctrl_mmr_unlock()
> in board_init_f() before enable_mcu_esm_reset()?
>
> Is it TIFS firmware?
> What else could be affected?
> Do we expect to leave General Purpose Control Registers unlocked
> when we return from board_init_f()?
> Does it mean that the whole ctrl_mmr_unlock() has to be re-done
> after k3_sysfw_loader() call?

I really can't tell why those registers are locked again. I figured out 
they're only locked again after loading the TIFS firmware on HS-SE 
devices. So, I also assume the firmware itself locks those registers 
again as part of a secure/security feature.

The A53 SPL will unlock those registers again, which will be permanent. 
Only the watchdog is problematic because enable_mcu_esm_reset is 
currently only called in the R5 SPL (config only enabled in the R5 SPL 
defconfig).

BTW: We have seen the same behavior with the AM68A/J721S2.

- Daniel

>
>> Signed-off-by: Daniel Schultz <d.schultz@phytec.de>
>> ---
>>   arch/arm/mach-k3/am62x/am625_init.c | 3 +++
>>   1 file changed, 3 insertions(+)
>>
>> diff --git a/arch/arm/mach-k3/am62x/am625_init.c b/arch/arm/mach-k3/am62x/am625_init.c
>> index a422919fab1..498bbe45b38 100644
>> --- a/arch/arm/mach-k3/am62x/am625_init.c
>> +++ b/arch/arm/mach-k3/am62x/am625_init.c
>> @@ -84,6 +84,9 @@ static void ctrl_mmr_unlock(void)
>>   
>>   static __maybe_unused void enable_mcu_esm_reset(void)
>>   {
>> +	/* CTRLMMR_MCU_RST registers are locked again on HS-SE devices */
>> +	mmr_unlock(MCU_CTRL_MMR0_BASE, 6);
>> +
>>   	/* Set CTRLMMR_MCU_RST_CTRL:MCU_ESM_ERROR_RST_EN_Z  to '0' (low active) */
>>   	u32 stat = readl(CTRLMMR_MCU_RST_CTRL);
>>