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

[Sven Peter <sven@kernel.org>]

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@intel.com>
>> Closes: 
>> https://lore.kernel.org/oe-kbuild-all/202607181046.OANjIoqR-lkp@intel.com/
>> Signed-off-by: Sven Peter <sven@kernel.org>
>> ---
>>  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