Re: [PATCH 2/2] scsi: Align queue to ARCH_DMA_MINALIGN innon-coherent DMA mode

[陈华才 <chenhc@lemote.com>]

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);