linux-kernel - Re: [PATCH] net: mediatek: use dma_zalloc

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Message-ID: <20180719141723.GM17271@n2100.armlinux.org.uk>
Date:   Thu, 19 Jul 2018 15:17:23 +0100
From:   Russell King - ARM Linux <linux@...linux.org.uk>
To:     YueHaibing <yuehaibing@...wei.com>
Cc:     davem@...emloft.net, nbd@...nwrt.org, john@...ozen.org,
        sean.wang@...iatek.com, nelson.chang@...iatek.com,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mediatek@...ts.infradead.org, matthias.bgg@...il.com,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] net: mediatek: use dma_zalloc_coherent instead of
 allocator/memset

On Thu, Jul 19, 2018 at 10:09:55PM +0800, YueHaibing wrote:
> Use dma_zalloc_coherent instead of dma_alloc_coherent
> followed by memset 0.
> 
> Signed-off-by: YueHaibing <yuehaibing@...wei.com>
> ---
>  drivers/net/ethernet/mediatek/mtk_eth_soc.c | 7 ++-----
>  1 file changed, 2 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/net/ethernet/mediatek/mtk_eth_soc.c b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
> index d8ebf0a..fbdb3e3 100644
> --- a/drivers/net/ethernet/mediatek/mtk_eth_soc.c
> +++ b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
> @@ -1221,14 +1221,11 @@ static int mtk_tx_alloc(struct mtk_eth *eth)
>  	if (!ring->buf)
>  		goto no_tx_mem;
>  
> -	ring->dma = dma_alloc_coherent(eth->dev,
> -					  MTK_DMA_SIZE * sz,
> -					  &ring->phys,
> -					  GFP_ATOMIC | __GFP_ZERO);
> +	ring->dma = dma_zalloc_coherent(eth->dev, MTK_DMA_SIZE * sz,
> +					&ring->phys, GFP_ATOMIC | __GFP_ZERO);
>  	if (!ring->dma)
>  		goto no_tx_mem;
>  
> -	memset(ring->dma, 0, MTK_DMA_SIZE * sz);

I have to wonder whether this code needs two forms of zeroing... in
the original code, __GFP_ZERO _and_ a call to memset() just in case
__GFP_ZERO failed to do its job, and in the replacement code, just
in case dma_zalloc_coherent() hasn't got the idea...

I think you can drop the __GFP_ZERO. ;)

-- 
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
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