Re: [PATCH v2 1/7] of/fdt: Consolidate duplicate code into helper functions

Rob Herring
2025-11-13T22:39:01Z

On Thu, Nov 13, 2025 at 11:50:58PM +0800, Yuntao Wang wrote:
> Currently, there are many pieces of nearly identical code scattered across
> different places. Consolidate the duplicate code into helper functions to
> improve maintainability and reduce the likelihood of errors.
>
> Signed-off-by: Yuntao Wang <yuntao.wang@linux.dev>
> ---
> drivers/of/fdt.c | 41 +++++++++++++++++++++++++++++++++++++++++
> include/linux/of_fdt.h | 5 +++++
> 2 files changed, 46 insertions(+)
>
> diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
> index 0edd639898a6..5e0eabc1449f 100644
> --- a/drivers/of/fdt.c
> +++ b/drivers/of/fdt.c
> @@ -625,6 +625,47 @@ const void *__init of_get_flat_dt_prop(unsigned long node, const char *name,
> return fdt_getprop(initial_boot_params, node, name, size);
> }
>
> +const __be32 *__init of_fdt_get_addr_size_prop(unsigned long node,
> + const char *name, int *entries)
> +{
> + const __be32 *prop;
> + int len, elen = (dt_root_addr_cells + dt_root_size_cells) * sizeof(__be32);
> +
> + prop = of_get_flat_dt_prop(node, name, &len);
> + if (!prop) {
> + *entries = 0;
> + return NULL;
> + }
> +
> + if (len % elen) {
> + *entries = -1;

I don't think it's really important to distinguish a length error from
any other error. Either we can read the property or we can't.

> + return NULL;
> + }
> +
> + *entries = len / elen;
> + return prop;
> +}
> +
> +bool __init of_fdt_get_addr_size(unsigned long node, const char *name,
> + u64 *addr, u64 *size)
> +{
> + const __be32 *prop;
> + int len, elen = (dt_root_addr_cells + dt_root_size_cells) * sizeof(__be32);

Still have 2 locations to get the same calculation wrong...

> +
> + prop = of_get_flat_dt_prop(node, name, &len);
> + if (!prop || len < elen)
> + return false;

Why doesn't calling of_fdt_get_addr_size_prop() work here? If 'len <
elen', then 'len % elen' will also be true except in the 0 length case.
For that case, of_fdt_get_addr_size_prop() needs to handle it too.

> +
> + of_fdt_read_addr_size(prop, addr, size);
> + return true;
> +}
> +
> +void __init of_fdt_read_addr_size(const __be32 *prop, u64 *addr, u64 *size)
> +{
> + *addr = dt_mem_next_cell(dt_root_addr_cells, &prop);
> + *size = dt_mem_next_cell(dt_root_size_cells, &prop);
> +}
> +
> /**
> * of_fdt_is_compatible - Return true if given node from the given blob has
> * compat in its compatible list
> diff --git a/include/linux/of_fdt.h b/include/linux/of_fdt.h
> index b8d6c0c20876..3a0805ff6c7b 100644
> --- a/include/linux/of_fdt.h
> +++ b/include/linux/of_fdt.h
> @@ -55,6 +55,11 @@ extern int of_get_flat_dt_subnode_by_name(unsigned long node,
> const char *uname);
> extern const void *of_get_flat_dt_prop(unsigned long node, const char *name,
> int *size);
> +extern const __be32 *of_fdt_get_addr_size_prop(unsigned long node,
> + const char *name, int *entries);
> +extern bool of_fdt_get_addr_size(unsigned long node, const char *name,
> + u64 *addr, u64 *size);
> +extern void of_fdt_read_addr_size(const __be32 *prop, u64 *addr, u64 *size);
> extern int of_flat_dt_is_compatible(unsigned long node, const char *name);

Looks like of_flat_dt_* would be more consistent with existing naming.

> extern unsigned long of_get_flat_dt_root(void);
> extern uint32_t of_get_flat_dt_phandle(unsigned long node);
> --
> 2.51.0
>