Re: [PATCH RFC] arm64: tegra: Add reserved-memory node for P3450

[Aaron Kling <webgeek1234@gmail.com>]

On Mon, May 26, 2025 at 2:07 PM Aaron Kling <webgeek1234@gmail.com> wrote:
>
> On Mon, May 26, 2025 at 2:06 PM Aaron Kling via B4 Relay
> <devnull+webgeek1234.gmail.com@kernel.org> wrote:
> >
> > From: Aaron Kling <webgeek1234@gmail.com>
> >
> > The Tegra210 L4T bootloader ram training will corrupt the in-ram kernel
> > dt if no reserved-memory node exists. This prevents said bootloader from
> > being able to boot a kernel without this node, unless a chainloaded
> > bootloader loads the dt. Add the node to eliminate the requirement for
> > extra boot stages.
> >
> > Signed-off-by: Aaron Kling <webgeek1234@gmail.com>
> > ---
> >  arch/arm64/boot/dts/nvidia/tegra210-p3450-0000.dts | 6 ++++++
> >  1 file changed, 6 insertions(+)
> >
> > diff --git a/arch/arm64/boot/dts/nvidia/tegra210-p3450-0000.dts b/arch/arm64/boot/dts/nvidia/tegra210-p3450-0000.dts
> > index 0ecdd7243b2eb1abba9adbe9a404b226c29b85ef..8fc995e71696f2ef5e662a21feb96ea771c7a53f 100644
> > --- a/arch/arm64/boot/dts/nvidia/tegra210-p3450-0000.dts
> > +++ b/arch/arm64/boot/dts/nvidia/tegra210-p3450-0000.dts
> > @@ -22,6 +22,12 @@ chosen {
> >                 stdout-path = "serial0:115200n8";
> >         };
> >
> > +       reserved-memory {
> > +               #address-cells = <2>;
> > +               #size-cells = <2>;
> > +               ranges;
> > +       };
> > +
> >         memory@80000000 {
> >                 device_type = "memory";
> >                 reg = <0x0 0x80000000 0x1 0x0>;
> >
> > ---
> > base-commit: 0ff41df1cb268fc69e703a08a57ee14ae967d0ca
> > change-id: 20250526-p3450-mts-bug-02394af31f0a
> >
> > Best regards,
> > --
> > Aaron Kling <webgeek1234@gmail.com>
>
> This was sent as an RFC to see if there are any better solutions to
> this problem. Mts in l4t r32 for t210 tries to copy the training data
> to the reserved ram location provided by the kernel dt. But if that
> node doesn't exist, it somehow corrupts that dt, causing later stage
> boot stages and the kernel itself to fail. Since software support for
> this hardware is EOL, no fix for the bug can be expected. The normal
> Linux boot flow on this hardware involves placing the downstream dt in
> both the bootloader-dtb and kernel-dtb slots, allowing mts to work,
> then u-boot loading whatever dt the kernel expects. However, my use
> for Android does not need u-boot, as nvidia's cboot can load a
> standard android boot image without the extra complexity of additional
> boot stages. And I would prefer to keep complexity to a minimum. It
> should be noted that this affects p2371-2180 using the L4T bootloader
> as well, but since I am using the Android bootloader there, I sidestep
> the issue.
>
> Are there any thoughts on how to handle this problem? I know that it
> is typically undesirable to add broken bootloader workarounds to the
> kernel dt. But it would be preferable to have a fix upstream, instead
> of having to carry various workarounds in downstream forks.

Friendly reminder about this question.

Aaron