linux-kernel - Re: [PATCH V5 2/3] mm: dmapool: Align to ARCH_DMA

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Date:   Mon, 18 Sep 2017 14:55:08 +0800
From:   "陈华才" <chenhc@...ote.com>
To:     "Christoph Hellwig" <hch@...radead.org>
Cc:     "Andrew Morton" <akpm@...ux-foundation.org>,
        "Fuxin Zhang" <zhangfx@...ote.com>,
        "linux-mm" <linux-mm@...ck.org>,
        "linux-kernel" <linux-kernel@...r.kernel.org>,
        "stable" <stable@...r.kernel.org>
Subject: Re: [PATCH V5 2/3] mm: dmapool: Align to ARCH_DMA_MINALIGN innon-coherent DMA mode

Hi, Christoph,

Maybe you missed something.
1, pool_alloc_page() use dma_alloc_coherent() to allocate pool pages, and of course these pages are aligned to  ARCH_DMA_MINALIGN.
2, dma_pool_alloc() is the element allocator, but it doesn't use dma_alloc_coherent(). Elements only align to pool->size, but pool->size is usually less than ARCH_DMA_MINALIGN.
3, ARCH_DMA_MINALIGN is now only used in serveral drivers, no dma_ops use it.

Huacai

------------------ Original ------------------
From:  "Christoph Hellwig"<hch@...radead.org>;
Date:  Mon, Sep 18, 2017 01:22 PM
To:  "Huacai Chen"<chenhc@...ote.com>;
Cc:  "Andrew Morton"<akpm@...ux-foundation.org>; "Fuxin Zhang"<zhangfx@...ote.com>; "linux-mm"<linux-mm@...ck.org>; "linux-kernel"<linux-kernel@...r.kernel.org>; "stable"<stable@...r.kernel.org>;
Subject:  Re: [PATCH V5 2/3] mm: dmapool: Align to ARCH_DMA_MINALIGN innon-coherent DMA mode

The dmapool code uses dma_alloc_coherent to allocate each element,
and dma_alloc_coherent must align to ARCH_DMA_MINALIGN already.
If you implementation doesn't do that it needs to be fixed.