linux-kernel - Re: [PATCH] mtd: spi-nor: cqspi: remove duplicate const

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Date:   Tue, 27 Jun 2017 22:21:47 +0200
From:   Cyrille Pitchen <cyrille.pitchen@...ev4u.fr>
To:     Marek Vasut <marek.vasut@...il.com>, Arnd Bergmann <arnd@...db.de>,
        David Woodhouse <dwmw2@...radead.org>,
        Brian Norris <computersforpeace@...il.com>,
        Boris Brezillon <boris.brezillon@...e-electrons.com>,
        Richard Weinberger <richard@....at>
Cc:     linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mtd: spi-nor: cqspi: remove duplicate const

Le 27/06/2017 à 21:51, Marek Vasut a écrit :
> On 06/27/2017 09:48 PM, Cyrille Pitchen wrote:
>> Le 27/06/2017 à 18:11, Marek Vasut a écrit :
>>> On 06/27/2017 05:34 PM, Arnd Bergmann wrote:
>>>> The variable was already marked 'const' before the previous
>>>> patch, but the qualifier was in an unusual place, and now the
>>>> extra 'const' causes a harmless warning:
>>>>
>>>> drivers/mtd/spi-nor/cadence-quadspi.c:1286:34: error: duplicate 'const' declaration specifier [-Werror=duplicate-decl-specifier]
>>>>
>>>> This removes the other 'const' instead.
>>>
>>> Isn't that const array const elements , thus two consts ?
>>> IMO the original code is correct.
>>
>> Indeed the 2 'const' don't have the same meaning so the original code
>> may be correct but with an array like cqspi_dt_ids[] we can't write
>> "cqspi_dt_ids = (const struct of_device_id *)<right value>;" anyway.
> 
> Not sure I understand what you're trying to say here.
>

Just that once an array like cqspi_dt_ids[] has been defined, you can
never assign it a new value later:

cqspi_dt_ids = <new value>; /* that doesn't work */

For this specific point, an array behaves like a constant pointer (but
otherwise I agree that arrays and constant pointers are not the same
things). So I guess the 2nd 'const' could be considered as implicit :)



>> So I think the 2nd 'const' is useless here then if this patch removes a
>> warning, let's apply it, right?
>>
>>>
>>>> Fixes: f993c123b461 ("mtd: spi-nor: cqspi: make of_device_ids const")
>>>> Signed-off-by: Arnd Bergmann <arnd@...db.de>
>>>> ---
>>>>  drivers/mtd/spi-nor/cadence-quadspi.c | 2 +-
>>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/mtd/spi-nor/cadence-quadspi.c b/drivers/mtd/spi-nor/cadence-quadspi.c
>>>> index d315c326e72f..53c7d8e0327a 100644
>>>> --- a/drivers/mtd/spi-nor/cadence-quadspi.c
>>>> +++ b/drivers/mtd/spi-nor/cadence-quadspi.c
>>>> @@ -1283,7 +1283,7 @@ static const struct dev_pm_ops cqspi__dev_pm_ops = {
>>>>  #define CQSPI_DEV_PM_OPS	NULL
>>>>  #endif
>>>>  
>>>> -static const struct of_device_id const cqspi_dt_ids[] = {
>>>> +static const struct of_device_id cqspi_dt_ids[] = {
>>>>  	{.compatible = "cdns,qspi-nor",},
>>>>  	{ /* end of table */ }
>>>>  };
>>>>
>>>
>>>
>>
> 
>