linux-mips
[Top] [All Lists]

Re: [PATCH v6 2/2] of: Make of_find_node_by_path() traverse /aliases for

To: David Daney <ddaney.cavm@gmail.com>, linux-mips@linux-mips.org, ralf@linux-mips.org, devicetree-discuss@lists.ozlabs.org, Rob Herring <rob.herring@calxeda.com>
Subject: Re: [PATCH v6 2/2] of: Make of_find_node_by_path() traverse /aliases for relative paths.
From: Grant Likely <grant.likely@secretlab.ca>
Date: Thu, 08 Mar 2012 18:33:24 -0700
Cc: linux-kernel@vger.kernel.org, David Daney <david.daney@cavium.com>
In-reply-to: <1330543264-18103-3-git-send-email-ddaney.cavm@gmail.com>
References: <1330543264-18103-1-git-send-email-ddaney.cavm@gmail.com> <1330543264-18103-3-git-send-email-ddaney.cavm@gmail.com>
Sender: linux-mips-bounce@linux-mips.org
On Wed, 29 Feb 2012 11:21:04 -0800, David Daney <ddaney.cavm@gmail.com> wrote:
> From: David Daney <david.daney@cavium.com>
> 
> Currently all paths passed to of_find_node_by_path() must begin with a
> '/', indicating a full path to the desired node.
> 
> Augment the look-up code so that if a path does *not* begin with '/',
> the path is used as the name of an /aliases property.  The value of
> this alias is then used as the full node path to be found.
> 
> Signed-off-by: David Daney <david.daney@cavium.com>
> ---
>  drivers/of/base.c |   65 ++++++++++++++++++++++++++++++++++++++++++++++++++--
>  1 files changed, 62 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/of/base.c b/drivers/of/base.c
> index 5806449..0bbe47c 100644
> --- a/drivers/of/base.c
> +++ b/drivers/of/base.c
> @@ -365,22 +365,81 @@ EXPORT_SYMBOL(of_get_next_child);
>  
>  /**
>   *   of_find_node_by_path - Find a node matching a full OF path
> - *   @path:  The full path to match
> + *   @path: Either the full path to match, or if the path does not
> + *          start with '/', the name of a property of the /aliases
> + *          node (an alias).  In the case of an alias, the node
> + *          matching the alias' value will be returned.
>   *
>   *   Returns a node pointer with refcount incremented, use
>   *   of_node_put() on it when done.
>   */
>  struct device_node *of_find_node_by_path(const char *path)
>  {
> -     struct device_node *np = allnodes;
> +     struct device_node *np = NULL;
> +     struct device_node *aliases = NULL;
> +     char *alias = NULL;
> +     char *new_path = NULL;
> +     char *ps;
>  
>       read_lock(&devtree_lock);
> -     for (; np; np = np->allnext) {
> +
> +     /*
> +      * The following code has three possibilities:
> +      * 1) '/' at start of string; path == ps; (based at root)
> +      * 2) '/' at offset in string; path < ps; (relative to alias)
> +      * 3) '/' not found; ps == NULL; (alias only)
> +      *
> +      * If ps != path, then it is either a pure alias (ps == NULL),
> +      * or an alias with a relative path (path < ps).  Either way,
> +      * look up the path pointed to by the alias.
> +      */
> +     ps = strchr(path, '/');
> +     if (path != ps) {
> +             aliases = of_find_node_by_path("/aliases");
> +             if (!aliases)
> +                     goto out;
> +
> +             /*
> +              * Duplicate the alias part of the string so it can be
> +              * NULL terminated.
> +              */
> +             alias = kstrndup(path,
> +                              ps ? (ps - path) : strlen(path), GFP_KERNEL);
> +             if (!alias)
> +                     goto out;
> +             path = of_get_property(aliases, alias, NULL);
> +             if (!path || path[0] != '/')
> +                     goto out;

All the aliases are already decoded at boot time now.  See
of_alias_scan().  Instead of open-coding this, you can add an
of_alias_lookup() function something like this (untested):

const char *of_alias_lookup(const char *alias)
{
        struct alias_prop *app;
        list_for_each_entry(app, &aliases_lookup, link) {
                if (strcmp(app->alias, alias))
                        return app->np->full_name;
        }
        return NULL;
}

Then most of the above code disappears.  It can instead look like:

        ps = strchr(path, '/');
        if (path != ps) {
                char alias[ps - path + 1];
                strncpy(alias, path, ps - path);
                alias[ps - path] = '\0';
                path = of_alias_lookup(alias);
                if (path && ps)
                        /* Don't forget to free this */
                        path = kasprintf(GFP_KERNEL, "%s%s", path, ps);
                if (!path)
                        return NULL;
        }

g.

> +
> +             /* If ps is not NULL, then there is a relative path to append */
> +             if (ps) {
> +                     new_path = kzalloc(strlen(path) + strlen(ps) + 1,
> +                                        GFP_KERNEL);
> +                     if (!new_path)
> +                             goto out;
> +
> +                     sprintf(new_path, "%s%s", path, ps);
> +                     path = new_path;
> +             }
> +     }
> +
> +     /*
> +      * At this point, path now points to the full unaliased path
> +      * to a node, regardless of whether or not it started with an
> +      * alias.
> +      */
> +
> +     for (np = allnodes; np; np = np->allnext) {
>               if (np->full_name && (of_node_cmp(np->full_name, path) == 0)
>                   && of_node_get(np))
>                       break;
>       }
> +out:
> +     if (aliases)
> +             of_node_put(aliases);
>       read_unlock(&devtree_lock);
> +     kfree(alias);
> +     kfree(new_path);
>       return np;
>  }
>  EXPORT_SYMBOL(of_find_node_by_path);
> -- 
> 1.7.2.3
> 

-- 
email sent from notmuch.vim plugin

<Prev in Thread] Current Thread [Next in Thread>