Re: [PATCH] spl: Align device tree blob address at 8-byte boundary

Simon Glass
2021-07-13T16:47:29Z

Hi Marek,

On Tue, 13 Jul 2021 at 08:53, Marek Vasut <marex@denx.de> wrote:
>
> On 7/13/21 4:41 PM, Tom Rini wrote:
> > On Tue, Jul 13, 2021 at 04:35:38PM +0200, Marek Vasut wrote:
> >> On 7/13/21 3:47 PM, Tom Rini wrote:
> >>> On Mon, Jul 12, 2021 at 11:01:24AM -0500, Alex G. wrote:
> >>>> On 7/12/21 10:15 AM, Tom Rini wrote:
> >>>>> On Mon, Jul 12, 2021 at 01:36:14PM +0800, Bin Meng wrote:
> >>>>>> On Mon, Jul 12, 2021 at 1:21 PM Reuben Dowle <reuben.dowle@4rf.com> wrote:
> >>>>>>>
> >>>>>>> I submitted an almost identical patch. See https://github.com/u-boot/u-boot/commit/eb39d8ba5f0d1468b01b89a2a464d18612d3ea76
> >>>>>>>
> >>>>>>> This patch eventually had to be reverted (https://github.com/u-boot/u-boot/commit/5675ed7cb645f5ec13958726992daeeed16fd114), because it was causing issues on some platforms that had FIT on 32 bit boundary. However I continue to use it in production code, as without it the boot on my platform aborts.
> >>>>>>>
> >>>>>>> I don't have time to investigate why this was happening, but you need to check this code won't just cause exactly the same faults.
> >>>>>>
> >>>>>> Thanks for your information.
> >>>>>>
> >>>>>> +Marek who did the revert
> >>>>>>
> >>>>>> The revert commit message says:
> >>>>>>
> >>>>>> "The commit breaks booting of fitImage by SPL, the system simply
> >>>>>> hangs. This is because on arm32, the fitImage and all of its content
> >>>>>> can be aligned to 4 bytes and U-Boot expects just that."
> >>>>>>
> >>>>>> I don't understand this. If an address is aligned to 8, it is already
> >>>>>> aligned to 4, so how did this commit make the system hang on arm32?
> >>>>>
> >>>>> I think this had something to do with embedding contents somewhere in
> >>>>> the image? There is a thread on the ML from then but I don't know how
> >>>>> informative it will end up being.
> >>>>
> >>>> It's true that the flat devicetree spec requires an 8-byte alignment, even
> >>>> on 32-bit. The issues here are specific to u-boot.
> >>>>
> >>>> SPL and u-boot have to agree where u-boot's FDT is located. We'll look at
> >>>> two cases:
> >>>> 1) u-boot as a FIT (binary and FDT separately loaded)
> >>>> 2) u-boot with embedded FDT
> >>>>
> >>>> In case (1) SPL must place the FDT at a location where u-boot will find it.
> >>>> The current logic is
> >>>> SPL: fdt = ALIGN_4(u_boot + u_boot_size)
> >>>> u-boot: fdt = ALIGN_4(u_boot + u_boot_size)
> >>>>
> >>>> In case (2), SPL's view of the FDT is not relevant, but instead the build
> >>>> system must place the FDT correctly:
> >>>> build: fdt >> u-boot.bin
> >>>> u-boot: fdt = ALIGN_4(u_boot + u_boot_size)
> >>>>
> >>>> We have 3 places that must agree. A correct and complete patch could change
> >>>> all three, but one has to consider compatibility issues when crossing u-boot
> >>>> and SPL versions.
> >>>>
> >>>> I had proposed in the revert discussion that SPL use r2 or similar mechanism
> >>>> to pass the location of the FDT to u-boot.
> >>>
> >>> I'm not sure that we need to worry too much about mix-and-match
> >>> SPL/U-Boot, but documenting what to go change if you must do it
> >>> somewhere under doc/ would be good. I think we can just switch to
> >>> ALIGN(8) not ALIGN(4) and be done with it?
> >>
> >> Remember, there is also falcon boot. And we definitely have to be able to
> >> have old u-boot (SPL) boot new fitImage and vice versa.
> >
> > I don't follow you, sorry. But since you seem to have the best
> > understanding of where all of the cases something could go wrong here,
> > can you perhaps post an RFC patch? That is likely to be clearer than
> > another long thread here.
>
> I don't follow you, sorry. I believe the revert did the right thing and
> new systems should use mkimage -E when generating fitImages, to avoid
> the string alignment problem. That is all.

Using -E should be optional and things really should work without it.

Regards,
Simon