linux-kernel - Re: I need help with a sparse warning

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Date:	Fri, 12 Sep 2008 13:12:12 -0400
From:	Pavel Roskin <proski@....org>
To:	Larry Finger <Larry.Finger@...inger.net>
Cc:	Roland Dreier <rdreier@...co.com>,
	LKML <linux-kernel@...r.kernel.org>,
	wireless <linux-wireless@...r.kernel.org>
Subject: Re: I need help with a sparse warning

On Thu, 2008-09-11 at 22:05 -0500, Larry Finger wrote:
> > I would guess you want something like:
> > 
> > 	priv->rx_mtu = le16_to_cpu(((__force __le16 *) bootrec->data)[20]);
> > 
> > (__force is what shuts up sparse, and as far as I can see, the size_t
> > cast is useless, since the result will be promoted anyway)
> 
> Yes, that one works. As you suspected, this section is parsing data 
> from the firmware.

I believe __force should be the last resort.  If you want to read a
16-bit little endian value at the given offset, I suggest that you use
le16_to_cpup(), which operates on pointers and does the cast for you.

A better but more elaborate solution would be to define a structure that
would have __le16 rx_mtu at the offset 40.  Then you can cast bootrec to
that structure and apply le16_to_cpu() to that field.

-- 
Regards,
Pavel Roskin
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