Re: [PATCH] OF: base: match each node compatible against all given matches first

[Thierry Reding <thierry.reding-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

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On Thu, Nov 28, 2013 at 07:36:25PM +0100, Sebastian Hesselbarth wrote:
> Currently, of_match_node compares each given match against all node's
> compatible strings with of_device_is_compatible.
> 
> To achieve multiple compatible strings per node with ordering from
> specific to generic, this requires given matches to be ordered from
> specific to generic. For most of the drivers this is not true and also
> an alphabetical ordering is more sane there.
> 
> Therefore, this patch modifies of_match_node to match each of the node's
> compatible strings against all given matches first, before checking the
> next compatible string. This implies that node's compatibles are ordered
> from specific to generic while given matches can be in any order.
> 
> Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
> ---
> Cc: Grant Likely <grant.likely-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
> Cc: Rob Herring <rob.herring-bsGFqQB8/DxBDgjK7y7TUQ@public.gmane.org>
> Cc: Benjamin Herrenschmidt <benh-XVmvHMARGAS8U2dJNN8I7kB+6BGkLq7r@public.gmane.org>
> Cc: Russell King <linux-lFZ/pmaqli7XmaaqVzeoHQ@public.gmane.org>
> Cc: devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
> Cc: linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org
> Cc: linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
> ---
>  drivers/of/base.c |   47 ++++++++++++++++++++++++++++++++---------------
>  1 file changed, 32 insertions(+), 15 deletions(-)

Hi Sebastian,

I think you're one in a long line of people attempting to fix this. I
tried myself over a year ago (commit 107a84e61cdd 'of: match by
compatible property first') but it caused a subtle regression late in
the release cycle and was reverted (commit bc51b0c22ceb 'Revert "of:
match by compatible property first").

Only recently there was another attempt [0] but it's pretty much
equivalent to what I did back then.

That said, I think you might actually have nailed it with this patch.
From what I remember all earlier attempt failed because they didn't
match all compatible/name/type combinations properly. I'm adding a few
people on Cc who were involved with the other patches, perhaps they can
give your patch a spin and see if it fixes things for them.

Thierry

[0]: https://lkml.org/lkml/2013/10/3/585

> diff --git a/drivers/of/base.c b/drivers/of/base.c
> index 7d4c70f..183a9c7 100644
> --- a/drivers/of/base.c
> +++ b/drivers/of/base.c
> @@ -713,23 +713,37 @@ static
>  const struct of_device_id *__of_match_node(const struct of_device_id *matches,
>  					   const struct device_node *node)
>  {
> +	const char *cp;
> +	int cplen, l;
> +
>  	if (!matches)
>  		return NULL;
>  
> -	while (matches->name[0] || matches->type[0] || matches->compatible[0]) {
> -		int match = 1;
> -		if (matches->name[0])
> -			match &= node->name
> -				&& !strcmp(matches->name, node->name);
> -		if (matches->type[0])
> -			match &= node->type
> -				&& !strcmp(matches->type, node->type);
> -		if (matches->compatible[0])
> -			match &= __of_device_is_compatible(node,
> -							   matches->compatible);
> -		if (match)
> -			return matches;
> -		matches++;
> +	cp = __of_get_property(node, "compatible", &cplen);
> +	if (!cp)
> +		return NULL;
> +
> +	while (cplen > 0) {
> +		const struct of_device_id *m = matches;
> +
> +		while (m->name[0] || m->type[0] || m->compatible[0]) {
> +			int match = 1;
> +			if (m->name[0])
> +				match &= node->name
> +					&& !strcmp(m->name, node->name);
> +			if (m->type[0])
> +				match &= node->type
> +					&& !strcmp(m->type, node->type);
> +			if (m->compatible[0])
> +				match &= !of_compat_cmp(cp, m->compatible,
> +							strlen(m->compatible));
> +			if (match)
> +				return m;
> +			m++;
> +		}
> +		l = strlen(cp) + 1;
> +		cp += l;
> +		cplen -= l;
>  	}
>  	return NULL;
>  }
> @@ -739,7 +753,10 @@ const struct of_device_id *__of_match_node(const struct of_device_id *matches,
>   *	@matches:	array of of device match structures to search in
>   *	@node:		the of device structure to match against
>   *
> - *	Low level utility function used by device matching.
> + *	Low level utility function used by device matching. Matching order
> + *	is to compare each of the node's compatibles with all given matches
> + *	first. This implies node's compatible is sorted from specific to
> + *	generic while matches can be in any order.
>   */
>  const struct of_device_id *of_match_node(const struct of_device_id *matches,
>  					 const struct device_node *node)
> -- 
> 1.7.10.4
> 
> 
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