Re: [SPAM]Re: [PATCH] net: mediatek: use dma_zalloc_coherent instead of allocator/memset
From: Russell King - ARM Linux <hidden>
Date: 2018-07-20 08:13:34
Also in:
linux-arm-kernel, linux-mediatek
On Fri, Jul 20, 2018 at 02:30:53PM +0800, YueHaibing wrote:
On 2018/7/20 1:02, Sean Wang wrote:quoted
On Thu, 2018-07-19 at 15:17 +0100, Russell King - ARM Linux wrote:quoted
On Thu, Jul 19, 2018 at 10:09:55PM +0800, YueHaibing wrote:quoted
Use dma_zalloc_coherent instead of dma_alloc_coherent followed by memset 0. Signed-off-by: YueHaibing <redacted> --- 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. ;)Just now I did an experiment on 4.14.56 on armv7. I found that dma_zalloc_coherent does not guarantee that the buffer we get is all filled with 0. I really think it's a little bit weird OR what was I missing something for enabling dma_zalloc_coherent ? The result seems to tell that we can't remove freely the memset with 0 at this moment until we get a cause.That means dma_zalloc_coherent doesn't work as expect on armv7?
Can someone work out which underlying allocator is being used - the possibilities are: - dma_alloc_from_dev_coherent - cma - simple - remap - pool Looking at the code, I'd guess it's the pool allocator, as I don't see anything which zeros memory there, and it doesn't honor the __GFP_ZERO flag. This is definitely an allocator bug. -- RMK's Patch system: http://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line in suburbia: sync at 13.8Mbps down 630kbps up According to speedtest.net: 13Mbps down 490kbps up