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

[Guenter Roeck]

On 3/20/24 12:14, Rob Herring wrote:
> On Mon, Mar 18, 2024 at 4:31 PM Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
> > 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.
> > >
> > > > Building nios2:10m50-ghrd:10m50_defconfig:10m50_devboard.dts ... running ...R failed (crashed)
> > >
> > > Booting with DT?
> > >
> > > > ------------
> > > > 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.
> >
> > For nios2, in early_init_devtree():
> >
> > void __init early_init_devtree(void *params)
> > {
> >           __be32 *dtb = (u32 *)__dtb_start;
> >          ...
> >           if (be32_to_cpu((__be32) *dtb) == OF_DT_HEADER)
> >                   params = (void *)__dtb_start;
> >
> > That worked fine until this patch. Starting with this patch, __dtb_start
> > always points to a valid empty devicetree blob, which overrides the
> > devicetree blob passed to early_init_devtree(). This causes the problem.
>
> With an external DTB, it doesn't boot with or without this patch. It
> just dies in different spots. Before it just skipped any memory

No, that is incorrect. Up to this patch it booted just fine with an
external dtb using the "-initrd" command line argument, and I explained
to you above why this is the case.

I guess you are saying I should stop boot testing nios2. I'll do just that.
Saves me resources and avoids discussions like this.

Guenter