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

[bb at ti.com]

On September 10, 2025 thus sayeth Sverdlin, Alexander:
> Hi Bryan!
> 
> On Wed, 2025-09-10 at 07:53 -0500, bb at 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

~Bryan