Let's talk about the complicated solution for a moment. Is there a way to reliably detect at install time whether a Power 7/8 system will need a prepboot partition? In other words, can we detect whether it has an SMS menu? And what are the two reasons to continue with creating it automatically?

Hello David.
Many versions of Petitboot exist and that makes any automagic difficult. Moreover, I'm not aware of any reliable way, how to easily read info about the flashed firmware without requiring additional tools. The missing PReP Boot can affect the default entry selection during the boot menu auto-generation and therefore this option requires some knowledge about the metal and admin who knows exactly what he wants to achieve. Therefore it's wiser/safer to keep the automatic PReP Boot creation intact and only allow a manual removal without blocking the whole installation.

Closing per comment #3.

Closed as notabug? I don't understand why.

(In reply to Jaromír Cápík from comment #5)
> Closed as notabug? I don't understand why.

Because there is no bug. There is no crash or other actual problem. Yes, it might be fun to support the latest thing, but this is something to play with in Fedora -- not RHEL.

(In reply to David Lehman from comment #6)
> (In reply to Jaromír Cápík from comment #5)
> > Closed as notabug? I don't understand why.
> 
> Because there is no bug. There is no crash or other actual problem. Yes, it
> might be fun to support the latest thing, but this is something to play with
> in Fedora -- not RHEL.

There is no crash, but the current behaviour IS a problem. Support "LATEST" thing? The thing is "LATEST" more than 3 years. Moreover, we decided to support Power8 in OPAL mode in RHEL 7.2 with introduction of PPC64LE.
You don't need to "play" with that. The only thing that is required is that you disable the prepboot presence check that prevents users from starting the installer.

Clarifying request based on IRC discussion:

The request is to turn the missing PReP condition from an error to a warning.
There is no request to change any defaults. This provides the petitboot/OPAL
user a way to opt out of PReP while limiting the likelihood that the
SMS/powervm user will mistakenly omit PReP.

NOTE: One more thing might be needed and that's a skip of grub installation if there's no target for storing the stage1 blob. PetitBoot only requires a valid grub.cfg generated as it parses the cfg content.

NOTE2: grub2-install apparently doesn't touch the prepboot content when the prepboot partition is not passed as argument. I successfully installed grub even without prepboot partition. The /boot/grub2 content got created.

*** Bug 1447195 has been marked as a duplicate of this bug. ***

This is still present in 7.4 and is obviously too late for 7.3.  Should we retarget to 7.5?

Regarding the initial description I think the question of POWER7 vs POWER8, SMS vs whatever is missing the point a bit.

The main distinction is between "pSeries" (KVM guest or PowerVM LPAR) and "PowerNV" (bare metal) contexts.  "pSeries" boots with Open Firmware and requires a PReP boot partition in most circumstances I'm aware of.  "PowerNV" boots with petitboot and doesn't require a PReP boot partition on any supported configuration.

Note that implementing this may require changes in the grub installer as well.  Right now I suspect it will error out if it can't write to a PReP boot partition, even though this step can be safely skipped on a PowerNV/petitboot machine.

Note that the PowerNV boot system is a bit magic.  Although we use the grub installer, GRUB is actually *never* executed during boot - which is why we can get away without putting the grub image anywhere.  Instead petitboot just knows how to read grub configuration and uses those to locate the kernels which it boots directly.

After evaluating this issue, there are no plans to address it further or fix it in an upcoming release.  Therefore, it is being closed.  If plans change such that this issue will be fixed in an upcoming release, then the bug can be reopened.