[PATCH 1/2] Documentation: devicetree: root node serial-number property documentation

[galak@codeaurora.org (Kumar Gala)]

> On Apr 16, 2015, at 1:14 PM, Paul Kocialkowski <contact@paulk.fr> wrote:
> 
> Le jeudi 16 avril 2015 ? 10:53 -0500, Kumar Gala a ?crit :
>>> On Apr 16, 2015, at 10:45 AM, Paul Kocialkowski <contact@paulk.fr> wrote:
>>> 
>>> Le jeudi 16 avril 2015 ? 10:23 -0500, Kumar Gala a ?crit :
>>>>> On Apr 16, 2015, at 9:36 AM, Rob Herring <robherring2@gmail.com> wrote:
>>>>> 
>>>>> On Thu, Apr 16, 2015 at 4:10 AM, Paul Kocialkowski <contact@paulk.fr> wrote:
>>>>>> Le jeudi 16 avril 2015 ? 09:56 +0200, Stefan Agner a ?crit :
>>>>>>> On 2015-03-28 18:39, Paul Kocialkowski wrote:
>>>>>>>> Signed-off-by: Paul Kocialkowski <contact@paulk.fr>
>>>>>>> 
>>>>>>> I think this is a worthwhile standardization.
>>>>>>> 
>>>>>>> Acked-by: Stefan Agner <stefan@agner.ch>
>>>>>> 
>>>>>> Thanks! I should also add a commit message in v2 mentioning that this is
>>>>>> already used in open firmware and reported by lshw.
>>>>> 
>>>>> With that,
>>>>> 
>>>>> Acked-by: Rob Herring <robh@kernel.org>
>>> 
>>> [snip]
>>> 
>>>> I feel like this is a little lite either in the doc or commit message.
>>>> Is the string completely arbitrary?  Is it meant to match labeling on
>>>> a board or case?  Is this meant to be used by the kernel at all?
>>> 
>>> I guess it doesn't really matter what it is, as long as it's a string.
>>> The kernel does not suggest any use for it either, it's just made
>>> available to userspace through cpuinfo.
>>> 
>>> Now if there is a particular use for this in user-space, it would have
>>> to match some standards. For instance, it Android, ro.serialno is
>>> usually a 16-bytes (plus one null byte) representation of a 64 bit
>>> number. For USB, I recall it is usually a 32 bytes string (including the
>>> null byte), but may be extended to more.
>>> 
>>> What the string actually represents depends and some SOCs have serial
>>> number bytes (I know that omap and sunxi have some for instance, that
>>> are usually used) while other devices may take it from somewhere else.
>>> In any case, it doesn't really matter and is not up to the kernel anyway
>>> since it is just passed through from the bootloader.
>>> 
>>> Thus, I don't think it's very relevant to mention it in either the
>>> documentation or the commit message.
>> 
>> So you say ?board? in the patch, since it could be SoC specific, we
>> should probably clean up the wording a bit.
> 
> It really doesn't matter where the string comes from, what it contains
> or whether some SoCs have provisions to generate one.
> I think board is one the most common words that we can use to describe
> devices. "devices" is also fine, I could go with it if you prefer, but I
> don't really see what it changes.

Lets go with device instead of board.

> 
>> I?m just saying when someone reads this 6 months or a year later and
>> tries to figure out what the purpose of the property is they don?t
>> really have enough info.  Putting some examples in the commit message
>> of what possibly usages is I think a reasonable thing.
> 
> Okay, that would make sense. Still, the purpose of this is to pass the
> serial number string from the bootloader to userspace. All of the
> discussion about where to grab the serial from and what it should look
> like is not relevant to the kernel. Instead, it's up to the bootloader
> that is in charge of generating the serial string, so the discussion
> should happen there.

Again, I?ve got no issues with the property and its purpose to be used by user space, just saying we need to convey more of the intent via commit message or updating the doc.

- k
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