linux-kernel - Re: [PATCH] leds: pca955x: fix -Wvoid-pointer-to-enum-cast warning

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Message-ID: <20230818160154.GZ986605@google.com>
Date:   Fri, 18 Aug 2023 17:01:54 +0100
From:   Lee Jones <lee@...nel.org>
To:     Justin Stitt <justinstitt@...gle.com>
Cc:     Pavel Machek <pavel@....cz>, Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>, linux-leds@...r.kernel.org,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH] leds: pca955x: fix -Wvoid-pointer-to-enum-cast warning

On Wed, 16 Aug 2023, Justin Stitt wrote:

> When building with clang 18 I see the following warning:
> |      drivers/leds/leds-pca955x.c:487:15: warning: cast to smaller integer
> |      type 'enum pca955x_type' from 'const void *' [-Wvoid-pointer-to-enum-cast]
> |        487 |                 chip_type = (enum pca955x_type)md;
> 
> This is due to the fact that `md` is a void* while `enum pca995x_type` has the
> size of an int.
> 
> Add uintptr_t cast to silence clang warning while also keeping enum cast
> for readability and consistency with other `chip_type` assignment just a
> few lines below:
> |	chip_type = (enum pca955x_type)id->driver_data;
> 
> Link: https://github.com/ClangBuiltLinux/linux/issues/1910
> Reported-by: Nathan Chancellor <nathan@...nel.org>

A review from Nathan would be good here.

> Signed-off-by: Justin Stitt <justinstitt@...gle.com>

Also please make checkpatch.pl happy before resending, thanks.

> ---
> 
> 
> leds: pca955x: fix -Wvoid-pointer-to-enum-cast warning
> ---
> Note: I've opted to keep the initial `enum pca955x_type` cast and just
> place the uintptr_t cast first to silence the warning. It seemed weird
> to me to see the same variable being assigned to two different casted
> values within just a few lines.
> ---
>  drivers/leds/leds-pca955x.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/leds/leds-pca955x.c b/drivers/leds/leds-pca955x.c
> index b10e1ef38db0..1d7fa0cd97bf 100644
> --- a/drivers/leds/leds-pca955x.c
> +++ b/drivers/leds/leds-pca955x.c
> @@ -484,7 +484,7 @@ static int pca955x_probe(struct i2c_client *client)
>  	const void *md = device_get_match_data(&client->dev);
>  
>  	if (md) {
> -		chip_type = (enum pca955x_type)md;
> +		chip_type = (enum pca955x_type)(uintptr_t)md;
>  	} else {
>  		const struct i2c_device_id *id = i2c_match_id(pca955x_id,
>  							      client);
> 
> ---
> base-commit: 2ccdd1b13c591d306f0401d98dedc4bdcd02b421
> change-id: 20230816-void-drivers-leds-leds-pca955x-7002cc67a291
> 
> Best regards,
> --
> Justin Stitt <justinstitt@...gle.com>
> 

-- 
Lee Jones [李琼斯]