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

[Joshua Peisach]

On Sun Jul 19, 2026 at 11:15 AM EDT, Sven Peter wrote:
> On 7/19/26 17:02, Joshua Peisach wrote:
> > 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 <lkp@xxxxxxxxx>
> > > Closes: 
> > > https://lore.kernel.org/oe-kbuild-all/202607181046.OANjIoqR-lkp@xxxxxxxxx/
> > > Signed-off-by: Sven Peter <sven@xxxxxxxxxx>
> > > ---
> > >  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 
> > > *pdev)
> > >  {
> > >      struct device *dev = &pdev->dev;
> > >      struct apple_smc *smc;
> > > -    u32 count;
> > > +    __be32 count;
> > >      int ret;
> > >
> > >      smc = devm_kzalloc(dev, sizeof(*smc), GFP_KERNEL);
> > > @@ -461,8 +461,10 @@ static int apple_smc_probe(struct 
> > > platform_device *pdev)
> > >      dev_set_drvdata(&pdev->dev, smc);
> > >      BLOCKING_INIT_NOTIFIER_HEAD(&smc->event_handlers);
> > >
> > > -    ret = apple_smc_read_u32(smc, SMC_KEY(#KEY), &count);
> > > -    if (ret)
> > > +    ret = apple_smc_read(smc, SMC_KEY(#KEY), &count, sizeof(count));
> > > +    if (ret >= 0 && ret != sizeof(count))
> > > +        ret = -EINVAL;
> > > +    if (ret < 0)
> > >          return dev_err_probe(smc->dev, ret, "Failed to get key count");
> > >      smc->key_count = 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).
>
> count is __be32 now (the SMC firmware returns that value as big-endian 
> because Apple likes to think different) and we read that using 
> apple_smc_read now which just reads raw bytes. be32_to_cpu then converts 
> that to a u32, i.e. the type of smc->key_count. There's no functional 
> change here. What's weird about that?
>
>
> Sven

Pfft, brain fart. I thought you were going other way around.

Reviewed-by: Joshua Peisach <jpeisach@xxxxxxxxxx>