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

[Tom Rini]

On Fri, Apr 09, 2021 at 05:29:36PM -0700, Tim Harvey wrote:
> On Fri, Apr 9, 2021 at 1:53 PM Tom Rini <trini at konsulko.com> wrote:
> >
> > 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.
> >
> 
> I just ran into this as well finding that commit 38d6b7ebdaee ("spl:
> Drop bd_info in the data section") breaks Gateworks Ventana and
> defining SPL_ALLOC_BD does resolve it. In this case, Falcon mode is
> not being used and the breakage is because arch/arm/mach-imx/spl.c
> dram_init_banksize() accesses gd->bd which is NULL.
> 
> So I would guess that this probably broke a whole lot of IMX based
> boards that use SPL.
> 
> I don't quite know what the best solution is... we now have a v2021.04
> that is broken for several or many boards and I dont' know if its
> clear what cases break.

Looking forward, I think we need to rework this.  Simon, I gather you
have some platforms where we need to set gd->bd to something that we
malloc() ?  So perhaps spl_set_bd() should have been __weak so that
architectures / platforms could override as needed, but also move it
just past mem_malloc_init().

-- 
Tom
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