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

Mon Apr 19 17:32:40 CEST 2021

On Tue, Apr 13, 2021 at 05:49:19AM +1200, Simon Glass wrote:
> Hi Tom, Alex,
> 
> On Tue, 13 Apr 2021 at 04:26, Tom Rini <trini at konsulko.com> wrote:
> >
> > On Mon, Apr 12, 2021 at 10:21:18AM -0500, Alex G. wrote:
> > >
> > >
> > > On 4/12/21 9:40 AM, Tom Rini wrote:
> > > > On Mon, Apr 12, 2021 at 08:51:11AM -0500, Alex G. wrote:
> > > > >
> > > > >
> > > > > On 4/12/21 8:25 AM, Tom Rini wrote:
> > > > > > 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().
> > > > >
> > > > > Let's try and avoid making new weak functions. Why not introduce a
> > > > > spl_platform_alloc_bd(), that each plat- *must* implement? No diversion to
> > > > > Kconfig and no __weak__ required.
> > > >
> > > > Well, who needs something different than what we had before exactly?
> > >
> > > I'm not sure. From reading the commit message of the broken change, it seems
> > > the main driver was to save 64 bytes on coral. I'm assuming coral is the
> > > codename for a platform.
> >
> > Yes, coral is an x86 chromebook.  It also says:
> >     This uses up space in the SPL binary but it always starts as zero.
> >     Also some boards cannot support data in TPL (e.g. Intel Apollo Lake).
> >
> > and defaults the new feature to enabled on all x86.  And there's
> > a comment about x86 in the function (that with the changes made isn't so
> > helpful/correct?) now too.  So yes, I want to see what Simon
> >
> > > > This shouldn't be kicked up to "every SoC must define...", but maybe
> > > > "every architecture must define..." is OK.  Or maybe it's really just "a
> > > > few unusual platforms need" and so a weak function makes sense.
> > >
> > > We can can have arch_spl_alloc_bd() instead of plat_(). I don't believe in
> > > weak functins, as I see them as the problems that "made sense at the time".
> >
> > I see weak functions as a good solution when the problem is something
> > where the majority of the (cross-platform) cases require the same
> > solution, but there's one or two oddities out there.  But regardless, we
> > need to have the problem better defined before we can propose a
> > solution.
> 
> So how about enabling the Kconfig for iMX? I am not sure how many
> platforms do actually need this feature?
> 
> Another option might be to (just as a test) take the 'bd' out of
> global_data when the Kconfig is not defined, to find out which
> platforms use it?

I started down the path of seeing what fails to build if in SPL we don't
have gd->bd, but well, then we get back to the OP, where Alex notes it's
all cases of falcon mode.  And Tim noted that i.MX is widely broken due
to setting up memory info as well more generally.  It looks like
Rockchip hits that and Marvell and probably a few others.

So I think the right answer is the revert, followed by figuring out how
to let x86 instead have a malloc'd one.  Perhaps spl_board_init() is
OK?

-- 
Tom
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