linux-kernel - Re: drivers/platform/x86/apple-gmux.c:276:15: sparse: sparse: cast to restricted _

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Message-Id: <D62B0A4F-6A2E-495D-B3AE-4CEAEE172E39@gmail.com>
Date:   Tue, 16 May 2023 21:31:16 +1000
From:   Orlando Chamberlain <orlandoch.dev@...il.com>
To:     Hans de Goede <hdegoede@...hat.com>
Cc:     kernel test robot <lkp@...el.com>, oe-kbuild-all@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: Re: drivers/platform/x86/apple-gmux.c:276:15: sparse: sparse: cast to restricted __be32

Hi,

> On 16 May 2023, at 8:27 pm, Hans de Goede <hdegoede@...hat.com> wrote:
> 
> Hi,
> 
>> On 5/16/23 12:16, kernel test robot wrote:
>> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
>> head:   f1fcbaa18b28dec10281551dfe6ed3a3ed80e3d6
>> commit: 0c18184de990e63f708b090bcb9fc6c0fbc427cd platform/x86: apple-gmux: support MMIO gmux on T2 Macs
>> date:   9 weeks ago
>> config: i386-randconfig-s001-20230515
>> compiler: gcc-11 (Debian 11.3.0-12) 11.3.0
>> reproduce:
>>        # apt-get install sparse
>>        # sparse version: v0.6.4-39-gce1a6720-dirty
>>        # https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=0c18184de990e63f708b090bcb9fc6c0fbc427cd
>>        git remote add linus https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
>>        git fetch --no-tags linus master
>>        git checkout 0c18184de990e63f708b090bcb9fc6c0fbc427cd
>>        # save the config file
>>        mkdir build_dir && cp config build_dir/.config
>>        make W=1 C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__' O=build_dir ARCH=i386 olddefconfig
>>        make W=1 C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__' O=build_dir ARCH=i386 SHELL=/bin/bash drivers/platform/x86/
>> 
>> If you fix the issue, kindly add following tag where applicable
>> | Reported-by: kernel test robot <lkp@...el.com>
>> | Link: https://lore.kernel.org/oe-kbuild-all/202305161712.5l3f4iI4-lkp@intel.com/
> 
> <snip>
> 
>> vim +276 drivers/platform/x86/apple-gmux.c
>> 
>>   265    
>>   266    static u32 gmux_mmio_read32(struct apple_gmux_data *gmux_data, int port)
>>   267    {
>>   268        u32 val;
>>   269    
>>   270        mutex_lock(&gmux_data->index_lock);
>>   271        gmux_mmio_wait(gmux_data);
>>   272        iowrite8((port & 0xff), gmux_data->iomem_base + GMUX_MMIO_PORT_SELECT);
>>   273        iowrite8(GMUX_MMIO_READ | sizeof(val),
>>   274            gmux_data->iomem_base + GMUX_MMIO_COMMAND_SEND);
>>   275        gmux_mmio_wait(gmux_data);
>>> 276        val = be32_to_cpu(ioread32(gmux_data->iomem_base));
> 
> Ok, so sparse does not like this line.
> 
>>   277        mutex_unlock(&gmux_data->index_lock);
>>   278    
>>   279        return val;
>>   280    }
>>   281    
>>   282    static void gmux_mmio_write32(struct apple_gmux_data *gmux_data, int port,
>>   283                       u32 val)
>>   284    {
>>   285        mutex_lock(&gmux_data->index_lock);
>>> 286        iowrite32(cpu_to_be32(val), gmux_data->iomem_base);
> 
> Nor this line. But this is what we want (convert to/from be32 to CPU
> when reading/writing).
> 
> There is iowrite32be() but that always unconditionally swabs
> the byte order independent of the CPU byte-order.
> 
> Now this is an x86 driver so always swapping is fine, still
> I wonder if there is a better option here then using
> iowrite32be() and ioread32be() ?

Thanks for finding those functions. I can't think of anything better unless there's a simple way to change sparse's rules so that it will be happy with code like this.

Regards,
Orlando

> 
> Regards,
> 
> Hans
> 
> 
> 
> 
>>   287        iowrite8(port & 0xff, gmux_data->iomem_base + GMUX_MMIO_PORT_SELECT);
>>   288        iowrite8(GMUX_MMIO_WRITE | sizeof(val),
>>   289            gmux_data->iomem_base + GMUX_MMIO_COMMAND_SEND);
>>   290        gmux_mmio_wait(gmux_data);
>>   291        mutex_unlock(&gmux_data->index_lock);
>>   292    }
>>   293    
>> 
>