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Subject: Re: [PATCH] mtd: spi-nor: cqspi: remove duplicate const
To: Cyrille Pitchen <cyrille.pitchen@wedev4u.fr>,
        Arnd Bergmann <arnd@arndb.de>, David Woodhouse <dwmw2@infradead.org>,
        Brian Norris <computersforpeace@gmail.com>,
        Boris Brezillon <boris.brezillon@free-electrons.com>,
        Richard Weinberger <richard@nod.at>
References: <20170627153508.1329697-1-arnd@arndb.de>
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 <6956fba6-ab14-fc53-1da2-c80df0adf85a@wedev4u.fr>
Cc: linux-mtd@lists.infradead.org, linux-kernel@vger.kernel.org
From: Marek Vasut <marek.vasut@gmail.com>
Message-ID: <819ac96e-0740-5855-5896-df2ac0242d0b@gmail.com>
Date: Tue, 27 Jun 2017 22:53:08 +0200
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On 06/27/2017 10:21 PM, Cyrille Pitchen wrote:
> 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 :)

I had to think about this a little and I think what you're getting at is
something slightly different.

IIUC if this was array of pointers (which it is not), you'd need this
const Type *const name[] , but since this is array of Type , you can do
with const Type name[] and the whole thing is implicitly const.

But in that case:
Acked-by: Marek Vasut <marek.vasut@gmail.com>

>>> 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@arndb.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 */ }
>>>>>  };
>>>>>
>>>>
>>>>
>>>
>>
>>
> 


-- 
Best regards,
Marek Vasut