The len value is in bytes, while `dt_root_addr_cells + dt_root_size_cells`
is in cells (4 bytes per cell).

The modulo calculation between them is incorrect, the units must be
converted first.

Fixes: fb319e77a0e7 ("of: fdt: Add memory for devices by DT property "linux,usable-memory-range"")
Signed-off-by: Yuntao Wang <yuntao.wang@linux.dev>
---
 drivers/of/fdt.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
index 716ebe8c23d3..0f95f3b356ea 100644
--- a/drivers/of/fdt.c
+++ b/drivers/of/fdt.c
@@ -859,7 +859,7 @@ void __init early_init_dt_check_for_usable_mem_range(void)
 	pr_debug("Looking for usable-memory-range property... ");
 
 	prop = of_get_flat_dt_prop(node, "linux,usable-memory-range", &len);
-	if (!prop || (len % (dt_root_addr_cells + dt_root_size_cells)))
+	if (!prop || len % dt_root_addr_size_bytes())
 		return;
 
 	endp = prop + (len / sizeof(__be32));
-- 
2.51.0

Hi Yuntao,

On Wed, 12 Nov 2025 at 15:38, Yuntao Wang <yuntao.wang@linux.dev> wrote:
> The len value is in bytes, while `dt_root_addr_cells + dt_root_size_cells`
> is in cells (4 bytes per cell).
>
> The modulo calculation between them is incorrect, the units must be
> converted first.

Thanks for your patch!

> Fixes: fb319e77a0e7 ("of: fdt: Add memory for devices by DT property "linux,usable-memory-range"")

That commit merely changed "<" to "%".

The code that added the bad expression was:
Fixes: 2af2b50acf9b9c38 ("of: fdt: Add generic support for handling
usable memory range property")
However, that code was copied from:
Fixes: 8f579b1c4e347b23 ("arm64: limit memory regions based on DT
property, usable-memory-range")

So I think you want to list these two Fixes-tags instead.

> Signed-off-by: Yuntao Wang <yuntao.wang@linux.dev>

For the actual change:
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds