[S] Change in coreboot[main]: soc/intel/cmn/pmc: Add support for early power off

[Subrata Banik (Code Review)]

Attention is currently required from: Angel Pons, Intel coreboot Reviewers, Julius Werner, Jérémy Compostella, Karthik Ramasubramanian.

Subrata Banik has posted comments on this change by Subrata Banik. ( https://review.coreboot.org/c/coreboot/+/86336?usp=email )

Change subject: soc/intel/cmn/pmc: Add support for early power off
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Patch Set 3:

(2 comments)

Patchset:

PS3:
> I disagree with #1 as detailed in the discussion found at the following link: [comment 21c234e0_b1965b7b](https://review.coreboot.org/c/coreboot/+/86336/comment/21c234e0_b1965b7b/).
>
> Regarding point #2, it appears to be a more reasonable approach than your previous proposal. Given that the limitation is specific to the System on Chip (SoC), it is sensible to manage it within the SoC-specific codebase.

Sure, there is no valid reason for calling PMC register as is from early power off as we know it doesn't work and would cause same effect/or worse like what halt() does.

I like the suggestion coming from Angel, which would even allow me to keep early power-off implementation inside ChromeOS vendor code.

File src/soc/intel/common/block/pmc/pmclib.c:

https://review.coreboot.org/c/coreboot/+/86336/comment/b48e9593_54fd7608?usp... :
PS3, Line 635: __weak void platform_do_early_poweroff(void)
> > Can you tell me the name of the Intel SoC that supports early shutdown using PMC? Based on my knowledge, there are currently no Intel SoCs that support common code with early shutdown capabilities. However, we can consider implementing a SoC-specific override if any future SoC enables early shutdown.
>
> I cannot provide you with a 100% guaranteed list of Intel SoCs where early shutdown is confirmed to be effective, as this scenario has not been formally tested, and I lack the resources to conduct such tests personally. However, based on my experience in the automotive industry working with SoCs like Apollo Lake, I believe that early shutdown was operational at early boot.

Based on my testing on all devices starting with SKL till latest PTL, no Intel chipset supports early power-off before MRC init is done using vanilla PMC register programming (it needs special handling). Therefore, there is no additional point of agreeing or disagreeing here. I understood your point and will modify the code.