linux-kernel - Re: [PATCH 1/2] of: base: add support to get machine model name

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Message-ID: <58331B5D.8060907@gmail.com>
Date:   Mon, 21 Nov 2016 08:05:49 -0800
From:   Frank Rowand <frowand.list@...il.com>
To:     Sudeep Holla <sudeep.holla@....com>, linux-kernel@...r.kernel.org,
        Rob Herring <robh+dt@...nel.org>
Cc:     Arnd Bergmann <arnd@...db.de>, devicetree@...r.kernel.org
Subject: Re: [PATCH 1/2] of: base: add support to get machine model name

Hi Sudeep,

On 11/18/16 12:22, Frank Rowand wrote:
> On 11/18/16 02:41, Sudeep Holla wrote:
>>
>>
>> On 17/11/16 21:00, Frank Rowand wrote:
>>> On 11/17/16 07:32, Sudeep Holla wrote:
>>>> Currently platforms/drivers needing to get the machine model name are
>>>> replicating the same snippet of code. In some case, the OF reference
>>>> counting is either missing or incorrect.
>>>>
>>>> This patch adds support to read the machine model name either using
>>>> the "model" or the "compatible" property in the device tree root node
>>>> to the core OF/DT code.
>>>>
>>>> This can be used to remove all the duplicate code snippets doing exactly
>>>> same thing later.
>>>
>>> I find five instances of reading only property "model":
>>>
>>>   arch/arm/mach-imx/cpu.c
>>>   arch/arm/mach-mxs/mach-mxs.c
>>>   arch/c6x/kernel/setup.c
>>>   arch/mips/cavium-octeon/setup.c
>>>   arch/sh/boards/of-generic.c
>>>
>>
>> Ah sorry you were not Cc-ed in 2/2, but that shows all the instances
>> that this will be used for.
> 
> I have not seen 2/2.  I do not see it on the devicetree list or on lkml.

Can you please re-send patch 2/2?

-Frank

> 
> I did see a list of drivers in the RFC patch that you sent several hours
> before this patch.
> 
> In that patch you replaced reading the model name from the _flat_ device
> tree with the new function in at least one location.  That is not
> correct.
> 
> 
>>
>>> I find one instance of reading property "model", then if
>>> that does not exist, property "compatible":
>>>
>>>   arch/mips/generic/proc.c
>>>
>>
>> Correct as you can check in patch 2/2
>>
>>> The proposed patch matches the code used in one place, and thus
>>> current usage does not match the patch description.
>>>
>>
>> Yes, but does it matter ? compatibles are somewhat informative about the
>> model IMO.
> 
> Yes it does matter.  That is just sloppy and makes devicetree yet harder
> to understand.  It hurts clarity.  The new function name says get "model",
> not get "model" or "first element of the compatible list".
> 
> And using the _first_ element only of the compatible list to determine
> model is not a good paradigm.  It is yet another hidden, special case,
> undocumented trap to lure in the unwary.
> 
> It is extremely unlikely that the change actually changes behavior for an
> existing device tree because there is probably no dts that does not
> contain the model property but does contain the proper magic value in
> the compatible property.  But did you actually check for that?
> 
>>
>>> Is my search bad?  Are you planning to add additional instances
>>> of reading "model" then "compatible"?
>>>
>>
>> No, just replacing the existing ones as in patch 2/2
>>
> 
> You also ignored Arnd's comment in reply to your RFC patch.
> 
> -Frank
>