Re: [Xen-devel] [PATCH v3 16/17] FDT: Add a helper to get specified name subnode

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Sat, 23 Jan 2016, Shannon Zhao wrote:
> From: Shannon Zhao <shannon.zhao@xxxxxxxxxx>
> 
> Sometimes it needs to check if there is a node in FDT by full path.
> Introduce this helper to get the specified name subnode if it exists.
> 
> Signed-off-by: Shannon Zhao <shannon.zhao@xxxxxxxxxx>
> ---
> CC: Rob Herring <robh@xxxxxxxxxx>
> ---
>  drivers/of/fdt.c       | 35 +++++++++++++++++++++++++++++++++++
>  include/linux/of_fdt.h |  2 ++
>  2 files changed, 37 insertions(+)
> 
> diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
> index 655f79d..112ec16 100644
> --- a/drivers/of/fdt.c
> +++ b/drivers/of/fdt.c
> @@ -645,6 +645,41 @@ int __init of_scan_flat_dt(int (*it)(unsigned long node,
>  }
>  
>  /**
> + * of_get_flat_dt_subnode_by_name - get subnode of specified node by name
> + *
> + * @node: the parent node
> + * @uname: the name of subnode
> + * @return offset of the subnode, or -FDT_ERR_NOTFOUND if there is none
> + */
> +
> +int of_get_flat_dt_subnode_by_name(unsigned long node, const char *uname)
> +{
> +     const void *blob = initial_boot_params;
> +     int offset;
> +     const char *pathp;
> +
> +     /* Find first subnode if it exists */
> +     offset = fdt_first_subnode(blob, node);
> +     if (offset < 0)
> +             return -FDT_ERR_NOTFOUND;
> +     pathp = fdt_get_name(blob, offset, NULL);
> +     if (strncmp(pathp, uname, strlen(uname)) == 0)
> +             return offset;

Wouldn't this check succeed even if uname is "uefi" and the node
name is actually "uefiiiii"?  You might have to use strcmp.


> +     /* Find other subnodes */
> +     do {
> +             offset = fdt_next_subnode(blob, offset);
> +             if (offset < 0)
> +                     return -FDT_ERR_NOTFOUND;
> +             pathp = fdt_get_name(blob, offset, NULL);
> +             if (strncmp(pathp, uname, strlen(uname)) == 0)
> +                     return offset;
> +     } while (offset >= 0);

Rather than writing the name check twice, I think it would be best to
code this loop as:

    for (offset = fdt_first_subnode(blob, offset);
         offset >= 0;
         offset = fdt_next_subnode(blob, offset)) {

         /* do name check */



> +     return -FDT_ERR_NOTFOUND;
> +}
> +
> +/**
>   * of_get_flat_dt_root - find the root node in the flat blob
>   */
>  unsigned long __init of_get_flat_dt_root(void)
> diff --git a/include/linux/of_fdt.h b/include/linux/of_fdt.h
> index df9ef38..fc28162 100644
> --- a/include/linux/of_fdt.h
> +++ b/include/linux/of_fdt.h
> @@ -52,6 +52,8 @@ extern char __dtb_end[];
>  extern int of_scan_flat_dt(int (*it)(unsigned long node, const char *uname,
>                                    int depth, void *data),
>                          void *data);
> +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 int of_flat_dt_is_compatible(unsigned long node, const char *name);
> -- 
> 2.0.4
> 
> 

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