linux-kernel - Re: [PATCH 2/2] scsi: Align queue to ARCH_DMA

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Message-ID: <tencent_164349390B49089A598FAEDB@qq.com>
Date:   Mon, 11 Sep 2017 16:41:51 +0800
From:   "陈华才" <chenhc@...ote.com>
To:     "Christoph Hellwig" <hch@...radead.org>
Cc:     "James E . J . Bottomley" 
        <jejb@...ux.vnet.ibm.com>,
        "Martin K . Petersen" 
        <martin.petersen@...cle.com>,
        "Fuxin Zhang" <zhangfx@...ote.com>,
        "linux-scsi" <linux-scsi@...r.kernel.org>,
        "linux-kernel" <linux-kernel@...r.kernel.org>,
        "stable" <stable@...r.kernel.org>
Subject: Re: [PATCH 2/2] scsi: Align queue to ARCH_DMA_MINALIGN innon-coherent DMA mode

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@...radead.org>;
Date:  Mon, Sep 11, 2017 03:39 PM
To:  "Huacai Chen"<chenhc@...ote.com>; 
Cc:  "James E . J . Bottomley"<jejb@...ux.vnet.ibm.com>; "Martin K . Petersen"<martin.petersen@...cle.com>; "Fuxin Zhang"<zhangfx@...ote.com>; "linux-scsi"<linux-scsi@...r.kernel.org>; "linux-kernel"<linux-kernel@...r.kernel.org>; "stable"<stable@...r.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);