Re: [PATCH] mfd: macsmc: Fix key count endianness annotation

On Sun Jul 19, 2026 at 9:00 AM EDT, Sven Peter wrote:
> SMC firmware returns the value of the #KEY key in big-endian unlike most
> other keys. Reading it through apple_smc_read_u32() into a plain u32
> and then converting with be32_to_cpu() makes sparse complain:
>
>   drivers/mfd/macsmc.c:462:26: sparse: cast to restricted __be32
>
> Read the raw value into a __be32 using apple_smc_read() instead.
>
> Fixes: e038d985c982 ("mfd: Add Apple Silicon System Management Controller=
")
> Reported-by: kernel test robot <[email protected]>
> Closes: https://lore.kernel.org/oe-kbuild-all/202607181046.OANjIoqR-lkp@i=
ntel.com/
> Signed-off-by: Sven Peter <[email protected]>
> ---
>  drivers/mfd/macsmc.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/mfd/macsmc.c b/drivers/mfd/macsmc.c
> index 358feec2d088..514cba7dc897 100644
> --- a/drivers/mfd/macsmc.c
> +++ b/drivers/mfd/macsmc.c
> @@ -410,7 +410,7 @@ static int apple_smc_probe(struct platform_device *pd=
ev)
>  {
>  	struct device *dev =3D &pdev->dev;
>  	struct apple_smc *smc;
> -	u32 count;
> +	__be32 count;
>  	int ret;
> =20
>  	smc =3D devm_kzalloc(dev, sizeof(*smc), GFP_KERNEL);
> @@ -461,8 +461,10 @@ static int apple_smc_probe(struct platform_device *p=
dev)
>  	dev_set_drvdata(&pdev->dev, smc);
>  	BLOCKING_INIT_NOTIFIER_HEAD(&smc->event_handlers);
> =20
> -	ret =3D apple_smc_read_u32(smc, SMC_KEY(#KEY), &count);
> -	if (ret)
> +	ret =3D apple_smc_read(smc, SMC_KEY(#KEY), &count, sizeof(count));
> +	if (ret >=3D 0 && ret !=3D sizeof(count))
> +		ret =3D -EINVAL;
> +	if (ret < 0)
>  		return dev_err_probe(smc->dev, ret, "Failed to get key count");
>  	smc->key_count =3D be32_to_cpu(count);

This makes sense, it just feels weird reading because u32 is.. not a
be32 (that gets passed into be32_to_cpu).

I guess it doesn't really matter.

-Josh