linux-kernel - Re: [PATCH v14 3/9] fw_cfg: fix sparse warnings in fw_cfg_sel

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Date:   Wed, 14 Feb 2018 22:46:39 +0200
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Marc-André Lureau <marcandre.lureau@...hat.com>
Cc:     linux-kernel@...r.kernel.org, bhe@...hat.com, slp@...hat.com,
        somlo@....edu, xiaolong.ye@...el.com
Subject: Re: [PATCH v14 3/9] fw_cfg: fix sparse warnings in
 fw_cfg_sel_endianness()

On Wed, Feb 14, 2018 at 03:18:44PM +0100, Marc-André Lureau wrote:
> The function is used for both LE & BE target type, use __force casting.
> 
> Fixes:
> $ make C=1 CF=-D__CHECK_ENDIAN__ drivers/firmware/qemu_fw_cfg.o
> 
> drivers/firmware/qemu_fw_cfg.c:55:33: warning: restricted __be16 degrades to integer
> drivers/firmware/qemu_fw_cfg.c:55:52: warning: restricted __le16 degrades to integer
> 
> Signed-off-by: Marc-André Lureau <marcandre.lureau@...hat.com>
> ---
>  drivers/firmware/qemu_fw_cfg.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/firmware/qemu_fw_cfg.c b/drivers/firmware/qemu_fw_cfg.c
> index 90f467232777..85e693287d87 100644
> --- a/drivers/firmware/qemu_fw_cfg.c
> +++ b/drivers/firmware/qemu_fw_cfg.c
> @@ -52,7 +52,9 @@ static DEFINE_MUTEX(fw_cfg_dev_lock);
>  /* pick appropriate endianness for selector key */
>  static inline u16 fw_cfg_sel_endianness(u16 key)
>  {
> -	return fw_cfg_is_mmio ? cpu_to_be16(key) : cpu_to_le16(key);
> +	return fw_cfg_is_mmio ?
> +		(u16 __force)cpu_to_be16(key) :
> +		(u16 __force)cpu_to_le16(key);
>  }
>  
>  /* read chunk of given fw_cfg blob (caller responsible for sanity-check) */

Well the caller does cpu_to_le16 on the result ...
All this makes my head spin.

IMHO what you want is a wrapper that does iowrite and iowritebe
rather than __force.


> -- 
> 2.16.1.73.g5832b7e9f2