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

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Message-ID: <0e90817e-1c05-4fa3-a6fd-8e755608a2c9@oss.qualcomm.com>
Date: Thu, 27 Nov 2025 12:48:01 +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 12:42, Krzysztof Kozlowski wrote:
>>
>> =
>>> --- 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.

... and in case it is still not obvious: I do not cast here to final
type, because that cast is the reason for the warning.

I cast to an intermediary type to help compiler suppressing the warning
- to integer representing the pointer. Unsigned long is not representing
pointers in the kernel. Integer type representing the pointer is
kernel_ulong_t, I think.

Once you have integer type representing the pointer, you do not need
further casts to enum.

> 


Best regards,
Krzysztof