Re: [RFC PATCH 0/1] riscv: dts: Allow BUILTIN_DTB for all socs

[Palmer Dabbelt]

On Tue, 20 Feb 2024 12:46:57 PST (-0800), alex@xxxxxxxx wrote:
> Hi Yangyu,
>
> On 20/02/2024 20:01, Yangyu Chen wrote:
> > The BUILTIN_DTB kernel feature on RISC-V only works on K210 SoC only. This
> > patch moved this configuration to entire riscv.
> >
> > Although BUILTIN_DTB is not a good choice for most platforms, it is likely
> > to be a debug feature when some bootloader will always override something
> > like the memory node in the device tree to adjust the memory size from SPD
> > or configuration resistor, which makes it hard to do some debugging. As an
> > example, some platforms with numa like sg2042 only support sv39 will fail
> > to boot when there is no ZONE_HIGHMEM patch with 128G memory. If we want

I guess that's a surprising one, but there's always some Kconfig entries 
that are necessary to set in order to get platforms to boot -- at a bare 
minimum errata and drivers, for example.

> Orthogonal to this patch, but if needs be, we can fix this issue with
> 128G on sv39 by changing the sv39 address space layout, we still have
> room to gain the 4G you miss, at that time I was pretty sure that amount
> of memory would come with sv48 :)

That seems like a reasonable way to go, as long as it's not overly 
complex.

> Thanks,
>
> Alex
>
>
> > a kernel without this patch to boot, we need to write the memory nodes
> > in the DT manually.
> >
> > Also, changing DT on some platforms is not easy. For Milk-V Pioneer, the
> > boot procedure is ZSBL -> OpenSBI -> LinuxBoot -> Linux. If DT gets
> > changed, OpenSBI or LinuxBoot may refuse to boot. And there is some bug on
> > LinuxBoot now which does not consume --dtb argument on kexec and always
> > uses DT from memory. So I would like to do debugging on DT using

I'd argue those are bootloader/firmware bugs.

> > BUILTIN_DTB, which makes it very simple, I can even install the kernel in
> > the distro's way and provide a kernel package for other users to test.
> >
> > Yangyu Chen (1):
> >    riscv: dts: Allow BUILTIN_DTB for all socs
> >
> >   arch/riscv/Kconfig                  | 16 ++++++++++++++-
> >   arch/riscv/Kconfig.socs             | 32 -----------------------------
> >   arch/riscv/boot/dts/Makefile        |  2 +-
> >   arch/riscv/boot/dts/canaan/Makefile |  2 --
> >   4 files changed, 16 insertions(+), 36 deletions(-)