linux-kernel - Re: [PATCH 3/3] i2c: rcar: Fix Wvoid-pointer-to-enum-cast warning

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Message-ID: <dbb94fb1-2f78-4bd2-9254-c435ab3325c0@oss.qualcomm.com>
Date: Thu, 27 Nov 2025 12:42:15 +0100
From: Krzysztof Kozlowski <krzysztof.kozlowski@....qualcomm.com>
To: Geert Uytterhoeven <geert@...ux-m68k.org>
Cc: Andi Shyti <andi.shyti@...nel.org>, Ray Jui <rjui@...adcom.com>,
        Scott Branden <sbranden@...adcom.com>,
        Broadcom internal kernel review list
 <bcm-kernel-feedback-list@...adcom.com>,
        Wolfram Sang <wsa+renesas@...g-engineering.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Magnus Damm <magnus.damm@...il.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <nick.desaulniers+lkml@...il.com>,
        Bill Wendling <morbo@...gle.com>,
        Justin Stitt <justinstitt@...gle.com>, linux-i2c@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-renesas-soc@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH 3/3] i2c: rcar: Fix Wvoid-pointer-to-enum-cast warning

On 27/11/2025 10:02, Geert Uytterhoeven wrote:
> Hi Krzysztof,
> 
> On Wed, 26 Nov 2025 at 19:23, Krzysztof Kozlowski
> <krzysztof.kozlowski@....qualcomm.com> wrote:
>> 'i2c_types' is an enum, thus cast of pointer on 64-bit compile test with
>> clang and W=1 causes:
>>
>>   i2c-rcar.c:1144:18: error: cast to smaller integer type 'enum rcar_i2c_type' from 'const void *' [-Werror,-Wvoid-pointer-to-enum-cast]
>>
>> One of the discussions in 2023 on LKML suggested warning is not suitable
>> for kernel.  Nothing changed in this regard since that time, so assume
>> the warning will stay and we want to have warnings-free builds.
>>
>> Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@....qualcomm.com>
> 
> Thanks for your patch!
> 
> =
>> --- a/drivers/i2c/busses/i2c-rcar.c
>> +++ b/drivers/i2c/busses/i2c-rcar.c
>> @@ -1141,7 +1141,7 @@ static int rcar_i2c_probe(struct platform_device *pdev)
>>         if (IS_ERR(priv->io))
>>                 return PTR_ERR(priv->io);
>>
>> -       priv->devtype = (enum rcar_i2c_type)of_device_get_match_data(dev);
>> +       priv->devtype = (kernel_ulong_t)of_device_get_match_data(dev);
> 
> Any specific reason you picked "kernel_ulong_t" instead of "unsigned long"?
> The former seems to be the least common option.

As I wrote in the first patch, because to my knowledge it is the
preferred form for holding driver data which are in general pointers. We
do not store pointers as unsigned long. It is also already used for the
driver data types - see include/linux/mod_devicetable.h.

> FWIW, the most common option is "uintptr_t", which torvalds doesn't like...

Because it is discouraged in the kernel.

https://lore.kernel.org/all/2023081004-lapped-handbag-0324@gregkh/


Best regards,
Krzysztof