[PATCH] Revert "spl: Drop bd_info in the data section"

[Tom Rini]

On Fri, Apr 09, 2021 at 03:24:41PM -0500, Adam Ford wrote:
> On Fri, Apr 9, 2021 at 2:20 PM Alex G. <mr.nuke.me at gmail.com> wrote:
> >
> > Hi Simon
> >
> > On 4/8/21 6:55 PM, Simon Glass wrote:
> > > Hi Alexandru,
> > >
> > > On Fri, 9 Apr 2021 at 04:56, Alexandru Gagniuc <mr.nuke.me at gmail.com> wrote:
> > >>
> > >> This reverts commit 38d6b7ebdaee3e0e8426ef1b9df88bdce8ae2e75.
> > >>
> > >> struct global_data contains a pointer to the bd_info structure. This
> > >> pointer was populated spl_set_bd() to a pre-allocated bd_info in the
> > >> ".data" section. The referenced commit replaced this mechanism to one
> > >> that uses malloc(). That new mechanism is only used if SPL_ALLOC_BD=y.
> > >> which very few boards do.
> > >>
> > >> The result is that (struct global_data)->bd is NULL in SPL on most
> > >> platforms. This breaks falcon mode, since arch_fixup_fdt() tries to
> > >> access (struct global_data)->bd and set the "/memory" node in the
> > >> devicetree. The result is that the "/memory" node contains garbage
> > >> values, causing linux to panic() as it sets up the page table.
> > >>
> > >> Instead of trying to fix the mess, potentially causing other issues,
> > >> revert to the code that worked, while this change is reworked.
> > >
> > > The goal here is to drop a feature that few boards use and reduce
> > > memory usage in SPL. It has been in place for two releases now.
> > >
> > > If Falcon mode needs it, perhaps you could add an 'imply' in the
> > > Kconfig for that feature? Is there one? Or perhaps
> > > CONFIG_ARCH_FIXUP_FDT_MEMORY ?
> > >
> > > One option would be to return an error in arch_fixup_fdt(). In
> > > general, fixups make things tricky because there is no way to
> > > determine when they are used but at least this one has a CONFIG.
> > >
> >
> > The argument that this has been in place for two releases is incorrect.
> > Commit 38d6b7ebdaee3e0e8426ef1b9df88bdce8ae2e75 was only introduced with
> > the v2021.04 release. It definitely was not in 2021.01. It's only in the
> > last release, which is four days old t the time of this writing.

Yes.  But another way of saying that is that we're 4 days in to the
merge window.  That's a bit early to say we must revert the change.  If
this was just before the release, yes, revert would be the right answer.
It's also the case the original commit fixes some cases while also
saving size, if I read it right.  So a strict revert isn't right, we'd
need to also probably also default y SPL_ALLOC_BD in some cases.

> > Although I was able to find one example, the reality is that we don't
> > know the full extent of the breakage. The prudent thing at this point is
> > to revert.
> >
> > The knowledge of how to init the platform is in the devicetree and code.
> > Why should kconfig also be involved in storing this knowledge? By this
> > model, as the number of boards increases without bounds, every "if"
> > predicate tends to be Kconfig driven. That is not maintainable, and why
> > I think the original change --and the proposed fixes-- are broken by design.
> >
> > Furthermore, I'm happy to discuss what to do about Falcon mode, and if
> > we should kill it entirely (I have an alternative proposal).  But we
> > shouldn't have that discussion in a manner holding my platform hostage.
> > To be fair to you, I don't think reverting a 64-byte savings in .data
> > will hold your platform hostage either.
> 
> That original patch broke a bunch of OMAP boards, but enabling
> SPL_ALLOC_BD was the solution to fix the issue.
> Can you try enabling SPL_ALLOC_BD and see if that fixes it?  Maybe we
> can make falcon mode imply it.

It would be "select" since it needs it rather than imply.

-- 
Tom
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