Re: [PATCH v19 05/13] of: Add a common kexec FDT setup function

On Tue, Jun 15, 2021 at 8:23 PM Michael Ellerman [off-list ref] wrote:

Rob Herring [off-list ref] writes:

quoted

On Tue, Jun 15, 2021 at 10:13 AM nramas [off-list ref] wrote:

quoted

On Tue, 2021-06-15 at 08:01 -0600, Rob Herring wrote:

quoted

On Tue, Jun 15, 2021 at 6:18 AM Geert Uytterhoeven <
geert@linux-m68k.org> wrote:

quoted

quoted

+void *of_kexec_alloc_and_setup_fdt(const struct kimage *image,
+                                  unsigned long
initrd_load_addr,
+                                  unsigned long initrd_len,
+                                  const char *cmdline, size_t
extra_fdt_size)
+{
+       /* Did we boot using an initrd? */
+       prop = fdt_getprop(fdt, chosen_node, "linux,initrd-
start", NULL);
+       if (prop) {
+               u64 tmp_start, tmp_end, tmp_size;
+
+               tmp_start = fdt64_to_cpu(*((const fdt64_t *)
prop));
+
+               prop = fdt_getprop(fdt, chosen_node,
"linux,initrd-end", NULL);
+               if (!prop) {
+                       ret = -EINVAL;
+                       goto out;
+               }
+
+               tmp_end = fdt64_to_cpu(*((const fdt64_t *)
prop));

Some kernel code assumes "linux,initrd-{start,end}" are 64-bit,
other code assumes 32-bit.

It can be either. The above code was a merge of arm64 and powerpc >> > both
of which use 64-bit and still only runs on those arches. It looks >> > like
some powerpc platforms may use 32-bit, but this would have been >> > broken
before.

quoted

quoted

of_kexec_alloc_and_setup_fdt() is called from elf_64.c (in
arch/powerpc/kexec) which is for 64-bit powerpc platform only.

64-bit PPC could be writing 32-bit property values. The architecture
size doesn't necessarily matter. And if the values came from the
bootloader, who knows what size it used.

This code is 32-bit powerpc only?:

arch/powerpc/boot/main.c-       /* Tell the kernel initrd address via device tree */
arch/powerpc/boot/main.c:       setprop_val(chosen, "linux,initrd-start", (u32)(initrd_addr));
arch/powerpc/boot/main.c-       setprop_val(chosen, "linux,initrd-end", (u32)(initrd_addr+initrd_size));

Historically that code was always built 32-bit, even when used with a
64-bit kernel.

These days it is also built 64-bit (for ppc64le).

How it is built is immaterial. It's always writing a 32-bit value due
to the u32 cast.

It looks like the drivers/of/fdt.c code can handle either 64 or 32-bit,
so I guess that's why it seems to be working.

Yes, that works, but that's not the issue. The question is does the
main.c code run in combination with kexec. The kexec code above
(copied straight from PPC code) would not work if linux,initrd-* are
written by the main.c code.

Rob