linux-kernel - Re: [PATCH] fix compiler warning in drivers/media/video/video-buf.c

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Message-Id: <20060928105108.88b37304.akpm@osdl.org>
Date:	Thu, 28 Sep 2006 10:51:08 -0700
From:	Andrew Morton <akpm@...l.org>
To:	Martin Bligh <mbligh@...gle.com>
Cc:	Sujoy Gupta <sujoy@...gle.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Mauro Carvalho Chehab <mchehab@...radead.org>,
	video4linux-list@...hat.com
Subject: Re: [PATCH] fix compiler warning in drivers/media/video/video-buf.c

On Thu, 28 Sep 2006 10:31:58 -0700
Martin Bligh <mbligh@...gle.com> wrote:

> Using a double cast to avoid compiler warnings when
> building for PAE. Compiler doesn't like direct casting
> of a 32 bit ptr to 64 bit integer.
> 
> ...
>
> diff -aurpN -X /home/mbligh/.diff.exclude linux-2.6.18/drivers/media/video/video-buf.c 2.6.18-videobuf/drivers/media/video/video-buf.c
> --- linux-2.6.18/drivers/media/video/video-buf.c	2006-06-17 18:49:35.000000000 -0700
> +++ 2.6.18-videobuf/drivers/media/video/video-buf.c	2006-09-28 10:28:54.000000000 -0700
> @@ -365,7 +365,12 @@ videobuf_iolock(struct videobuf_queue* q
>  		if (NULL == fbuf)
>  			return -EINVAL;
>  		/* FIXME: need sanity checks for vb->boff */
> -		bus   = (dma_addr_t)fbuf->base + vb->boff;
> +		/*
> +		 * Using a double cast to avoid compiler warnings when
> +		 * building for PAE. Compiler doesn't like direct casting 
> +		 * of a 32 bit ptr to 64 bit integer.
> +		 */
> +		bus   = (dma_addr_t)(size_t)fbuf->base + vb->boff;
>  		pages = PAGE_ALIGN(vb->size) >> PAGE_SHIFT;
>  		err = videobuf_dma_init_overlay(&vb->dma,PCI_DMA_FROMDEVICE,
>  						bus, pages);
> 

We normally cast pointers to unsigned long prior to assigning them to
64-bit values.  I'll make that change.

That being said, this driver is wrong to be storing dma addresses in a
void*.  And indeed there is a FIXME regarding this at
include/linux/videodev2.h:476, so I guess hiding this warning won't obscure
any fault which wasn't already known about..
-
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