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Date:   Fri, 26 Jan 2018 08:56:12 +0100
From:   Christoph Hellwig <hch@lst.de>
To:     Huacai Chen <chenhc@lemote.com>
Cc:     James Hogan <jhogan@kernel.org>, Christoph Hellwig <hch@lst.de>,
        Ralf Baechle <ralf@linux-mips.org>,
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        Fuxin Zhang <zhangfx@lemote.com>,
        Zhangjin Wu <wuzhangjin@gmail.com>,
        Jayachandran C <jchandra@broadcom.com>
Subject: Re: [PATCH 2/2] MIPS: Loongson64: Add cache_sync to
        loongson_dma_map_ops
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On Thu, Jan 25, 2018 at 04:44:36PM +0800, Huacai Chen wrote:
> Yes, kmalloc()'d memory with the appropriate GFP_DMA flags can be

You should never use GFP_DMA in kmalloc calls in new code.

> synced using the dma_map_*() and dma_unmap_*() functions. So,
> loongson_dma_map_page()/loongson_dma_unmap_page() (which is the
> backend of dma_map_*() and dma_unmap_*()) should call dma_cache_sync()
> for non-coherent devices, right?

No, it should call the internal dma sync for device/cpu calls, as already
explained by James.  Note that for 4.17 or 4.18 I plan to extent
the dma-direct work to not dma coherent systems, so we'll get an
explicit and document ABI for those across platforms.  That is if
I can pull it off as it doesn't seem entirely trivial.