Re: [PATCH v4 1/2] of: create of_root if no dtb provided

[Guenter Roeck]

On 3/18/24 12:26, Rob Herring wrote:
> +Stephen
>
> On Mon, Mar 18, 2024 at 12:09 PM Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
> > Hi,
> >
> > On Fri, Mar 17, 2023 at 12:34:14AM -0500, Frank Rowand wrote:
> > > When enabling CONFIG_OF on a platform where of_root is not populated by
> > > firmware, we end up without a root node. In order to apply overlays and
> > > create subnodes of the root node, we need one. Create this root node
> > > by unflattening an empty builtin dtb.
> > >
> > > If firmware provides a flattened device tree (FDT) then the FDT is
> > > unflattened via setup_arch().  Otherwise setup_of(), which is called
> > > immediately after setup_arch(), will create the default root node
> > > if it does not exist.
> > >
> > > Signed-off-by: Frank Rowand <frowand.list@xxxxxxxxx>
> >
> > This patch results in a crash on nios2.
>
> This patch was never applied. I assume you meant a later version of it
> that did get applied.

It is the patch in the link that was provided with the patch. What else
should we use as reference ? FWIW, I did look for a more recent version,
but I must have missed it. My bad.

> > Building nios2:10m50-ghrd:10m50_defconfig:10m50_devboard.dts ... running ...R failed (crashed)
>
> Booting with DT?

Yes, with arch/nios2/boot/dts/10m50_devboard.dtb.

> > ------------
> > qemu log: >> earlycon: uart8250 at MMIO32 0x18001600 (options '')
> > printk: legacy bootconsole [uart8250] enabled
> > Linux version 6.8.0-11409-gf6cef5f8c37f (groeck@desktop) (nios2-linux-gcc (GCC) 11.4.0, GNU ld (GNU Binutils) 2.40) #1 Sun Mar 17 23:38:59 PDT 2024
> > Kernel panic - not syncing: early_init_dt_alloc_memory_arch: Failed to allocate 72 bytes align=0x40
> > ---[ end Kernel panic - not syncing: early_init_dt_alloc_memory_arch: Failed to allocate 72 bytes align=0x40 ]---
>
> nios2 looks utterly broken to me. This change should be a nop unless
> initial_boot_params is NULL. It looks like it is possible for r6 (dtb
> address) to be 0 depending on kconfig options, but that would have
> skipped copying and unflattening which would then panic in
> setup_cpuinfo(). If initial_boot_params is not NULL, then the same
> early_init_dt_alloc_memory_arch() calls should fail when copying the
> DT. So I don't see how nios2 booting with DT ever worked.

All I can say that it did work with devicetree until this patch was
applied. It doesn't boot without it. I tried without devicetree file
after reverting this patch. That results in

Kernel panic - not syncing: setup_cpuinfo: No CPU found in devicetree!

Guenter