linux-kernel - Re: [PATCH v12 1/9] iomap: Fix sparse endian check warnings

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Date:   Sun, 18 Mar 2018 17:13:27 +0100
From:   Luc Van Oostenryck <luc.vanoostenryck@...il.com>
To:     Logan Gunthorpe <logang@...tatee.com>
Cc:     linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-ntb@...glegroups.com, linux-crypto@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Arnd Bergmann <arnd@...db.de>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Horia Geantă <horia.geanta@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Philippe Ombredanne <pombredanne@...b.com>,
        Kate Stewart <kstewart@...uxfoundation.org>
Subject: Re: [PATCH v12 1/9] iomap: Fix sparse endian check warnings

On Fri, Mar 16, 2018 at 09:48:44AM -0600, Logan Gunthorpe wrote:
> Warnings of the form:
> 
> lib/iomap.c:84:9: warning: cast to restricted __be16
> 
> Are found when running sparse checker with:
> 
> make C=2 CF=-D__CHECK_ENDIAN__
> 
> This patch casts them with __force to suppress the warnings.
 
Hi,

it looks correct but if you should explain why the warning
is not a valid one. Once done, you can then explain what problem
you have fixed instead of saying you suppressed a warning.

> Also, it looks like the wrong conversion function was used in

I would suggest to split the patch in two since it does two
different things which should have their own explanation.

> diff --git a/lib/iomap.c b/lib/iomap.c
> index 541d926da95e..a05d9fa21794 100644
> --- a/lib/iomap.c
> +++ b/lib/iomap.c
> @@ -106,8 +106,10 @@ EXPORT_SYMBOL(ioread32be);
>  #endif
>  
>  #ifndef mmio_write16be
> -#define mmio_write16be(val,port) __raw_writew(be16_to_cpu(val),port)
> -#define mmio_write32be(val,port) __raw_writel(be32_to_cpu(val),port)
> +#define mmio_write16be(val, port) \
> +	__raw_writew((u16 __force)cpu_to_be16(val), port)
> +#define mmio_write32be(val, port) \
> +	__raw_writel((u32 __force)cpu_to_be32(val), port)
>  #endif

I think that in this sort of replacement, it's better to not split
the lines (even if larger than 80, that's it).

-- Luc Van Oostenryck