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SubjectRe: [PATCH 2/2] scsi: Align queue to ARCH_DMA_MINALIGN innon-coherent DMA mode
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Hi, Christoph

I think we cannot modify dma_get_cache_alignment(), because existing callers may want to unconditionally return ARCH_DMA_MINALIGN.

Huacai


------------------ Original ------------------
From: "Christoph Hellwig"<hch@infradead.org>;
Date: Mon, Sep 11, 2017 03:39 PM
To: "Huacai Chen"<chenhc@lemote.com>;
Cc: "James E . J . Bottomley"<jejb@linux.vnet.ibm.com>; "Martin K . Petersen"<martin.petersen@oracle.com>; "Fuxin Zhang"<zhangfx@lemote.com>; "linux-scsi"<linux-scsi@vger.kernel.org>; "linux-kernel"<linux-kernel@vger.kernel.org>; "stable"<stable@vger.kernel.org>;
Subject: Re: [PATCH 2/2] scsi: Align queue to ARCH_DMA_MINALIGN innon-coherent DMA mode


> + if (plat_device_is_coherent(dev))

We can't just call platform device code. We'll need a proper
DMA API call for this.

> + blk_queue_dma_alignment(q, 0x04 - 1);
> + else
> + blk_queue_dma_alignment(q, dma_get_cache_alignment() - 1);

Which we already have with dma_get_cache_alignment, except that it
doesn't take a struct device pointer and doesn't call into dma_map
ops. So please add a struct device argument to dma_get_cache_alignment,
and let it call into dma_map_ops where needed.

With that you can replace the above with:

blk_queue_dma_alignment(q,
max(0x04U, dma_get_cache_alignment(dev)) - 1);
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