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Date: Thu, 03 Oct 2013 15:37:58 -0500
From: Rob Herring <robherring2@...il.com>
To: Marc Kleine-Budde <mkl@...gutronix.de>
CC: LKML <linux-kernel@...r.kernel.org>,
linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
Grant Likely <grant.likely@...aro.org>,
devicetree@...r.kernel.org,
"kernel@...gutronix.de" <kernel@...gutronix.de>
Subject: Re: [PATCH|RFC] of: let of_match_device() always return best match
On 10/03/2013 01:51 PM, Marc Kleine-Budde wrote:
> The function of_match_device() should tell if a struct device matches an
> of_device_id list and return the specific entry of that table matches the
> device best.
>
> The underlying __of_match_node() implements the wrong search algorithm. It
> iterates over the list of of_device_ids, comparing the first compatible with
> _all_ compatibles of the struct device, then the second compatible of
> of_device_id and so on.
>
> This leads to a problem, if the device has more than one compatible that match
> the of_device_id list. The implemented search algorithm may find not the "best"
> match. As the compatible list in the device is sorted from most to least
> specific.
>
> For example:
>
> The imx28.dtsi gives this compatible string for its CAN core:
>
>> compatible = "fsl,imx28-flexcan", "fsl,p1010-flexcan";
>
> The flexcan driver defines:
>
>> static const struct of_device_id flexcan_of_match[] = {
>> { .compatible = "fsl,p1010-flexcan", .data = &fsl_p1010_devtype_data, },
>> { .compatible = "fsl,imx28-flexcan", .data = &fsl_imx28_devtype_data, },
>> { .compatible = "fsl,imx6q-flexcan", .data = &fsl_imx6q_devtype_data, },
>> { /* sentinel */ },
>> };
>
> The "p1010" was the first Freescale SoC with the flexcan core. But this SoC has
> a bug, so a workaround has to be enabled in the driver. The mx28 has this bug
> fixed, so we don't need this quite costly workaround.
>
> The __of_match_node() will compare:
>
> from of_device_id from device
> fsl,p1010-flexcan fsl,imx28-flexcan
> fsl,p1010-flexcan fsl,p1010-flexcan -> MATCH
>
> The of_match_device() function as it currently is implemented will always
> return p1010 not the mx28.
>
> This patch fixes the problem by exchanging outer and inner loop. The first
> compatible of a device is compared against all compatible from the of_device_id
> list, then the second device compatible and so on.
This has been an issue for some time. A fix has been attempted before
and reverted if you look at the git history:
commit bc51b0c22cebf5c311a6f1895fcca9f78efd0478
Author: Linus Torvalds <torvalds@...ux-foundation.org>
Date: Tue Jul 10 12:49:32 2012 -0700
Revert "of: match by compatible property first"
This reverts commit 107a84e61cdd3406c842a0e4be7efffd3a05dba6.
Meelis Roos reports a regression since 3.5-rc5 that stops Sun Fire V100
and Sun Netra X1 sparc64 machines from booting, hanging after enabling
serial console. He bisected it to commit 107a84e61cdd.
Rob Herring explains:
"The problem is match combinations of compatible plus name and/or type
fail to match correctly. I have a fix for this, but given how late it
is for 3.5 I think it is best to revert this for now. There could be
other cases that rely on the current although wrong behavior. I will
post an updated version for 3.6."
Bisected-and-reported-by: Meelis Roos <mroos@...ux.ee>
Requested-by: Rob Herring <rob.herring@...xeda.com>
Cc: Thierry Reding <thierry.reding@...onic-design.de>
Cc: Grant Likely <grant.likely@...retlab.ca>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
There was also a fix attempted for this and the discussion here:
http://www.mail-archive.com/linuxppc-dev@lists.ozlabs.org/msg60163.html
You patch would hit the same issues I believe.
Rob
>
> Signed-off-by: Marc Kleine-Budde <mkl@...gutronix.de>
> ---
> drivers/of/base.c | 40 +++++++++++++++++++++++++++++++++++-----
> 1 file changed, 35 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/of/base.c b/drivers/of/base.c
> index 865d3f6..5bff2fe 100644
> --- a/drivers/of/base.c
> +++ b/drivers/of/base.c
> @@ -349,6 +349,35 @@ static int __of_device_is_compatible(const struct device_node *device,
> return 0;
> }
>
> +/** Returns the specific of_device_id, if the it matches one of the
> + * strings in the device's "compatible" property
> + */
> +static
> +const struct of_device_id *__of_device_matches_compatible(const struct device_node *device,
> + const struct of_device_id *matches)
> +{
> + const struct of_device_id *m;
> + const char* cp;
> + int cplen, l;
> +
> + cp = __of_get_property(device, "compatible", &cplen);
> + if (cp == NULL)
> + return NULL;
> + while (cplen > 0) {
> + m = matches;
> + while (m->compatible[0]) {
> + if (of_compat_cmp(cp, m->compatible, strlen(m->compatible)) == 0)
> + return m;
> + m++;
> + }
> + l = strlen(cp) + 1;
> + cp += l;
> + cplen -= l;
> + }
> +
> + return NULL;
> +}
> +
> /** Checks if the given "compat" string matches one of the strings in
> * the device's "compatible" property
> */
> @@ -717,22 +746,23 @@ const struct of_device_id *__of_match_node(const struct of_device_id *matches,
> {
> if (!matches)
> return NULL;
> -
> - while (matches->name[0] || matches->type[0] || matches->compatible[0]) {
> + while (matches->name[0] || matches->type[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++;
> }
> +
> + if (matches->compatible[0])
> + return __of_device_matches_compatible(node, matches);
> +
> return NULL;
> }
>
>
--
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