On 17/06/2025 19:13, Alejandro Vallejo wrote:
> The DT spec declares only two number types for a property: u32 and u64,
> as per Table 2.3 in Section 2.2.4. Remove unbounded loop and replace
> with a switch statement. Default to a size of 1 cell in the nonsensical
> size case, with a warning printed on the Xen console.
>
> Suggested-by: Daniel P. Smith" <dpsm...@apertussolutions.com>
> Signed-off-by: Alejandro Vallejo <agarc...@amd.com>
> ---
> v2:
> * Added missing `break` on the `case 2:` branch and added
> ASSERT_UNREACHABLE() to the deafult path
> ---
> xen/include/xen/device_tree.h | 17 ++++++++++++++---
> 1 file changed, 14 insertions(+), 3 deletions(-)
>
> diff --git a/xen/include/xen/device_tree.h b/xen/include/xen/device_tree.h
> index 75017e4266..2ec668b94a 100644
> --- a/xen/include/xen/device_tree.h
> +++ b/xen/include/xen/device_tree.h
> @@ -261,10 +261,21 @@ void intc_dt_preinit(void);
> /* Helper to read a big number; size is in cells (not bytes) */
> static inline u64 dt_read_number(const __be32 *cell, int size)
> {
> - u64 r = 0;
> + u64 r = be32_to_cpu(*cell);
> +
> + switch ( size )
> + {
> + case 1:
> + break;
> + case 2:
> + r = (r << 32) | be32_to_cpu(cell[1]);
> + break;
> + default:
> + // Nonsensical size. default to 1.
I wonder why there are so many examples of device trees in Linux with
#address-cells = <3>? Also, libfdt defines FDT_MAX_NCELLS as 4 with comment:
"maximum value for #address-cells and #size-cells" but I guess it follows the
IEE1275 standard and DT spec "is loosely related" to it.
~Michal
