linux-kernel - Re: [PATCH] Documentation DMA-API-HOWTO.txt Add dma mapping error check usage examples

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Date:	Thu, 18 Oct 2012 12:47:15 +0300
From:	Dan Carpenter <dan.carpenter@...cle.com>
To:	Shuah Khan <shuah.khan@...com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, konrad.wilk@...cle.com,
	rob@...dley.net, joerg.roedel@....com, shuahkhan@...il.com,
	devel@...uxdriverproject.org, linux-kernel@...r.kernel.org,
	linux-doc@...r.kernel.org
Subject: Re: [PATCH] Documentation DMA-API-HOWTO.txt Add dma mapping error
 check usage examples

On Sun, Oct 14, 2012 at 09:54:24AM -0600, Shuah Khan wrote:
> diff --git a/Documentation/DMA-API-HOWTO.txt b/Documentation/DMA-API-HOWTO.txt
> index a0b6250..cf1adb4 100644
> --- a/Documentation/DMA-API-HOWTO.txt
> +++ b/Documentation/DMA-API-HOWTO.txt
> @@ -468,11 +468,46 @@ To map a single region, you do:
>  	size_t size = buffer->len;
>  
>  	dma_handle = dma_map_single(dev, addr, size, direction);
> +	if (unlikely(dma_mapping_error(dma_handle))) {

Don't encourage people to put unlikely() and likely() into their
driver code.  It should only be used after benchmarking both with
and without.  I can't imagine how it would make a measurable
difference here.

regards,
dan carpenter


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