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

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Date:   Tue, 16 May 2023 12:27:42 +0200
From:   Hans de Goede <hdegoede@...hat.com>
To:     kernel test robot <lkp@...el.com>,
        Orlando Chamberlain <orlandoch.dev@...il.com>
Cc:     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 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() ?

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	
>