[PATCH 0/3] Revert HAFDBS changes

[Marc Zyngier]

Hi Pierre-Clément,

On Fri, 27 Oct 2023 10:49:47 +0100,
Pierre-Clément Tosi <ptosi at google.com> wrote:
> 
> Hi Chris,
> 
> On Fri, Oct 27, 2023 at 01:23:51PM +1300, Chris Packham wrote:
> > As discussed this series reverts the HAFDBS changes that caused an issue
> > on AC5/AC5X. I think there are some improvements that can be made to the
> > initial memory map for the AC5/AC5X but so far nothing I've found makes
> > it compatible with the HAFDBS changes.
> 
> Would you mind briefly explaining what those issues are and/or point
> me to the discussion where it was decided to revert these patches?

It was me[1] who offered to revert them, as the "fix" that Chris came
up with didn't make much sense on its own, was provided without much
of an explanation, and nobody else with sufficient understanding of
the ARMv8 translation model seem to have access to this HW to debug
it (though if someone sends me a board, I'll happily look into it).

To be clear, I'm pretty much convinced that the issue is due to the
way page tables are managed on the arm64 port. The whole "emergency
page table" switch doesn't make much sense, specially when changing
something as simple as some page attributes, and it isn't like "break
before make" is a brand new concept.

> The feature is quite useful for users of CONFIG_CMO_BY_VA_ONLY, to
> speed up the boot sequence: instead of reverting these patches
> altogether, would a reasonable alternative be to put them behind a
> build option?

I don't think this is right. Either we have something that works for
all ARMV8.1+ systems, or it just makes things a lot less maintainable.

But maybe the u-boot maintainers have a different view on this.

The core of the problem is that there is a truckload of code that
already exists in the tree and that somehow relies on the existing
(and funky) behaviours[2]. How do we go about fixing the core u-boot?
I have no idea.

Cheers,

	M.

[1] https://lore.kernel.org/r/063a16d559dc9cb327c9459803005006@kernel.org
[2] https://lore.kernel.org/r/CAFOYHZC_Dveax85n0fLr5BFyZcLqsvUssn=J0oHyvN75bTaCUw@mail.gmail.com

-- 
Without deviation from the norm, progress is not possible.