Re: [PATCH] Documentation DMA-API-HOWTO.txt Add dma mapping errorcheck usage examples

From: Dan Carpenter
Date: Thu Oct 18 2012 - 05:47:30 EST

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.

dan carpenter

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