netdev - RE: [PATCH] net: via-rhine: fix compiler warning

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Date:	Wed, 30 Apr 2014 08:49:39 +0000
From:	David Laight <David.Laight@...LAB.COM>
To:	'Jan Moskyto Matejka' <mq@...e.cz>,
	Alexey Charkov <alchark@...il.com>,
	Roger Luethi <rl@...lgate.ch>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] net: via-rhine: fix compiler warning

From: Jan Moskyto Matejka
> Fixed different size cast warning:
> 
> 	drivers/net/ethernet/via/via-rhine.c: In function rhine_init_one_platform:
> 	drivers/net/ethernet/via/via-rhine.c:1132:13: warning: cast from pointer to integer of different
> size [-Wpointer-to-int-cast]
> 	  revision = (u32)match->data;
> 		     ^
> 
> That code was added in commit 2d283862dc62daead9db0dc89cd0d0351e91f765
> ("net: via-rhine: add OF bus binding").
...
> diff --git a/drivers/net/ethernet/via/via-rhine.c b/drivers/net/ethernet/via/via-rhine.c
> index 4fa9201..76d18e0 100644
> --- a/drivers/net/ethernet/via/via-rhine.c
> +++ b/drivers/net/ethernet/via/via-rhine.c
> @@ -288,7 +288,7 @@ MODULE_DEVICE_TABLE(pci, rhine_pci_tbl);
>   * (for quirks etc.)
>   */
>  static struct of_device_id rhine_of_tbl[] = {
> -	{ .compatible = "via,vt8500-rhine", .data = (void *)0x84 },
> +	{ .compatible = "via,vt8500-rhine", .data = (u32 []) { 0x84 } },
>  	{ }	/* terminate list */
>  };
>  MODULE_DEVICE_TABLE(of, rhine_of_tbl);
> @@ -1129,7 +1129,7 @@ static int rhine_init_one_platform(struct platform_device *pdev)
>  	if (!irq)
>  		return -EINVAL;
> 
> -	revision = (u32)match->data;
> +	revision = *((u32 *) match->data);
>  	if (!revision)
>  		return -EINVAL;

Both those casts look horrid.
I'm not entirely convinced that the first is valid C - It would have to be
something specific to C99 initialisers.
Casts like *(u32 *)foo are also likely to be bugs (esp. on BE systems)
so themselves start ringing alarm bells.

So why not just:
	revision = (unsigned long)match->data;
and add a comment that the 0x84 is the revision - #define ??

	David