netdev - Re: [PATCH NET] ethtool: silence warning on bit loss

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Message-Id: <20161014.160625.256367812856122638.davem@davemloft.net>
Date:   Fri, 14 Oct 2016 16:06:25 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     jesse.brandeburg@...el.com
Cc:     netdev@...r.kernel.org
Subject: Re: [PATCH NET] ethtool: silence warning on bit loss

From: Jesse Brandeburg <jesse.brandeburg@...el.com>
Date: Thu, 13 Oct 2016 16:13:55 -0700

> Sparse was complaining when we went to prototype some code
> using ethtool_cmd_speed_set and SPEED_100000, which uses
> the upper 16 bits of __u32 speed for the first time.
> 
> CHECK
> ...
> .../uapi/linux/ethtool.h:123:28: warning:
>   cast truncates bits from constant value (186a0 becomes 86a0)
> 
> The warning is actually bogus, as no bits are really lost, but
> we can get rid of the sparse warning with this one small change.
> 
> Reported-by: Preethi Banala <preethi.banala@...el.com>
> Signed-off-by: Jesse Brandeburg <jesse.brandeburg@...el.com>

Ok, I'll apply this.

There were alternative suggestions but I like this patch
because it makes it explicit what is going on.

Just removing the u16 cast requires the reader to implicitly
understand and know the types in the structure.