Re: case sensitivity for devicetree node names

Re: case sensitivity for devicetree node names

[Frank Rowand]

Hi Ben,

(and adding other powerpc folks)

On 06/10/16 13:05, Frank Rowand wrote:
> I had assumed that devicetree node names were case sensitive. But a recent
> email thread asserted that they were not, which made me curious.
> 
> dtc treats node names as case sensitive:
> 
> $ cat test_node_case_1.dts
> 
> /dts-v1/;
> 
> / {
> 	node-x {
> 		prop_a = < 1 >;
> 	};
> };
> 
> / {
> 	node-X {
> 		prop_a = < 2 >;
> 	};
> };
> 
> $ cat test_node_case_2.dts
> 
> /dts-v1/;
> 
> / {
> 	node-x {
> 		prop_a = < 1 >;
> 	};
> };
> 
> / {
> 	node-x {
> 		prop_a = < 2 >;
> 	};
> };
> 
> $ dtc -O dts test_node_case_1.dts
> /dts-v1/;
> 
> / {
> 
> 	node-x {
> 		prop_a = <0x1>;
> 	};
> 
> 	node-X {
> 		prop_a = <0x2>;
> 	};
> };
> 
> $ dtc -O dts test_node_case_2.dts
> /dts-v1/;
> 
> / {
> 
> 	node-x {
> 		prop_a = <0x2>;
> 	};
> };
> 
> 
> But the Linux kernel source code defines of_node_cmp() as:
> 
>   include/linux/of.h:
> 
>   /* Default string compare functions, Allow arch asm/prom.h to override */
>   #if !defined(of_compat_cmp)
>   #define of_node_cmp(s1, s2) strcasecmp((s1), (s2))
> 
> arch/sparc/include/asm/prom.h uses strcmp() instead of strcasecmp().
> 
> Examples of using of_node_cmp() to check for a node name can be found,
> for example, of_find_node_by_name().
> 
> Is case insensitivity for node names a bug in the Linux kernel, or desired
> for some reason?
> 
> -Frank
> 

I chased through the history and found a 2.6.0-test5 announcement
which noted the patch from you which adds:

  of_find_node_by_path()
  of_find_node_by_name()
  of_find_node_by_type()
  of_find_compatible_node()

(And the patch is commit 394edd852a14 in the git recreation
of bitkeeper days, which is found at
git://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git)

That version of the functions uses a case insensitive compare for
devicetree node names.

Do you remember why you chose to not use a case sensitive compare?

Thanks,

-Frank

Re: case sensitivity for devicetree node names

[Benjamin Herrenschmidt]

On Sat, 2016-06-11 at 12:38 -0700, Frank Rowand wrote:
> I chased through the history and found a 2.6.0-test5 announcement
> which noted the patch from you which adds:
> 
>   of_find_node_by_path()
>   of_find_node_by_name()
>   of_find_node_by_type()
>   of_find_compatible_node()
> 
> (And the patch is commit 394edd852a14 in the git recreation
> of bitkeeper days, which is found at
> git://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git)
> 
> That version of the functions uses a case insensitive compare for
> devicetree node names.
> 
> Do you remember why you chose to not use a case sensitive compare?

>From memory, there were inconsistency in case on various earlier
machines (notably old macs). I think that's the main reason.

Cheers,
Ben.

Re: case sensitivity for devicetree node names

[Frank Rowand]

On 06/11/16 15:05, Benjamin Herrenschmidt wrote:
> On Sat, 2016-06-11 at 12:38 -0700, Frank Rowand wrote:
>> I chased through the history and found a 2.6.0-test5 announcement
>> which noted the patch from you which adds:
>>
>>   of_find_node_by_path()
>>   of_find_node_by_name()
>>   of_find_node_by_type()
>>   of_find_compatible_node()
>>
>> (And the patch is commit 394edd852a14 in the git recreation
>> of bitkeeper days, which is found at
>> git://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git)
>>
>> That version of the functions uses a case insensitive compare for
>> devicetree node names.
>>
>> Do you remember why you chose to not use a case sensitive compare?
> 
>>From memory, there were inconsistency in case on various earlier
> machines (notably old macs). I think that's the main reason.
> 
> Cheers,
> Ben.

Is there a kernel config option (or a small set of config options)
that would identify the affected machines?  It would be ok if
the option(s) also included some non-affected machines.  That
way we could use the case insensitive compare for a small
set of machines.

Re: case sensitivity for devicetree node names

[Benjamin Herrenschmidt]

On Sun, 2016-06-12 at 11:39 -0700, Frank Rowand wrote:
> 
> Is there a kernel config option (or a small set of config options)
> that would identify the affected machines?  It would be ok if
> the option(s) also included some non-affected machines.  That
> way we could use the case insensitive compare for a small
> set of machines.

Why do we want this ? Are there people really wanting to rely on case
difference between nodes ? That sounds fishy...

If you really want to do that, then CONFIG_PPC_PMAC would be your
test I suppose.

Cheers,
Ben.