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

Daniel Schultz
2025-09-10T14:06:41Z

On 9/10/25 15:26, bb@ti.com wrote:
> On September 10, 2025 thus sayeth Sverdlin, Alexander:
>> Hi Bryan!
>>
>> On Wed, 2025-09-10 at 07:53 -0500, bb@ti.com 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.
>>>>> Hmm yeah this is likely a bug or a config issue. Ideally we
>>>>> (U-Boot/Linux) should be in complete control of when these are locked or
>>>>> unlocked. TIFS or DM shouldn't be anywhere near these MMRs.
>>>>>
>>>>>> 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.
>>>>> Hmm this is strange.
>>>> Thanks for your assessment!
>>>> Do you know who can be contacted at TI regarding this possible problem in
>>>> TIFS firmware? Maybe this has to be fixed in TIFS firmware indeed?
>>> I've started creating some noise internally to see if we can debug this
>>> faster. Most of these teams are fairly insulated from the outside world
>>> and can only be reached via e2e tickets.
>> Thanks for looking into this!
>> I read it as if we would not need to create an e2e ticket for now?
> That's correct. I short circuited the e2e process by creating a bug and
> messaging a few people internally to jump start the process:
>
> https://sir.ext.ti.com/jira/browse/EXT_EP-12916

Just for reference, I already opened an e2e post some weeks ago:
https://e2e.ti.com/support/processors-group/processors/f/processors-forum/1511852/am625-am62x-hs-se-spl-cannot-write-to-mcu_mmr0_rst_ctrl/5813164#5813164

- Daniel

>
> ~Bryan