[PATCH] riscv: Only enable OF_BOARD_FIXUP for S-Mode

[Bin Meng]

On Sat, Sep 12, 2020 at 2:25 AM Sean Anderson <seanga2 at gmail.com> wrote:
>
> On 9/11/20 10:43 AM, Bin Meng wrote:
> > On Fri, Sep 11, 2020 at 6:20 PM Sean Anderson <seanga2 at gmail.com> wrote:
> >>
> >> On 9/11/20 3:29 AM, Bin Meng wrote:
> >>> Hi Sean,
> >>>
> >>> On Sat, Sep 5, 2020 at 9:22 PM Sean Anderson <seanga2 at gmail.com> wrote:
> >>>>
> >>>> It is unsafe to enable OF_BOARD_FIXUP only based on OF_SEPARATE.
> >>>> OF_SEPARATE may indicate that the user wishes U-Boot to use a different
> >>>> device tree than one obtained via OF_PRIOR_STAGE. However, OF_SEPARATE may
> >>>> also indicate that the device tree which would be obtained via
> >>>> OF_PRIOR_STAGE is invalid, nonexistant, or otherwise unusable. In this
> >>>
> >>> typo: nonexistent
> >>>
> >>>> latter case, enabling OF_BOARD_FIXUP will result in corruption of the
> >>>> device tree. To remedy this, only enable OF_BOARD_FIXUP if U-Boot is
> >>>> configured for S-Mode.
> >>>>
> >>>> Fixes: 1c17e55594a394ced7de88d91be294eaf8c564c1
> >>>
> >>> nits: the format should be: commit_id ("description")>
> >>>> Signed-off-by: Sean Anderson <seanga2 at gmail.com>
> >>>> ---
> >>>>
> >>>>  arch/riscv/Kconfig | 2 +-
> >>>>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>>>
> >>>> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> >>>> index 009a545fcf..13fac51483 100644
> >>>> --- a/arch/riscv/Kconfig
> >>>> +++ b/arch/riscv/Kconfig
> >>>> @@ -288,6 +288,6 @@ config STACK_SIZE_SHIFT
> >>>>         default 14
> >>>>
> >>>>  config OF_BOARD_FIXUP
> >>>> -       default y if OF_SEPARATE
> >>>> +       default y if OF_SEPARATE && RISCV_SMODE
> >>>
> >>> Is that your board is running U-Boot M-mode with OF_SEPARATE that does not work?
> >>
> >> Yes, because the reason we use OF_SEPARATE is because no device tree is
> >> passed to U-Boot. Trying to use the device tree passed to U-Boot even
> >
> > I don't get it. If no device tree is passed to U-Boot, why using
> > OF_SEPARATE in the first place?
>
> Because it has to come from somewhere. Where else would U-Boot get the
> device tree?

Sounds like there was some misunderstanding on "passed to U-Boot" ..
But I got it now.

>
> >> though OF_SEPARATE is enabled results in garbage being written to the
> >
> > What garbage data is written?
>
> It might not be garbage written. I didn't document the exact failure
> mode at the time I discovered this bug, so I went back to try and
> reproduce it for a more thorough analysis. However, I was unable to
> reproduce this bug, even on the branch where I originally triggered it.
> I documented my reasoning behind this patch at [1]. In my testing, I
> could only trigger a "periodic-32" bug.
>
> In any case, this behavior could still cause problems in the future.
> From my testing, on the k210, a1 usually holds some address on the ROM's
> stack. However, if it (for instance) instead held an address which

So U-Boot on K210 boots with M-mode from the K210 ROM, and the ROM
code does not hold DTB address in a1 before jumping to U-Boot, right?

> raised a load access fault, or was misaligned, then booting would fail.
> In the general case, I was very surpised that U-Boot was using the value
> of a1 on entry even with OF_SEPARATE specified. I would expect it only
> to use that value if configured with OF_PRIOR_STAGE.

Because U-Boot S-mode needs to fix up the DT when OF_SEPERATE is used.

>
> --Sean
>
> [1] https://patchwork.ozlabs.org/project/uboot/patch/20200815155237.467720-12-seanga2@gmail.com/#2520514

Regards,
Bin