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Subject: Re: [PATCH v2 27/32] scsi: hisi_sas: add smp protocol support
To: Arnd Bergmann <arnd@arndb.de>
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From: John Garry <john.garry@huawei.com>
Message-ID: <5637977E.7000704@huawei.com>
Date: Mon, 2 Nov 2015 17:03:58 +0000
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On 30/10/2015 16:22, John Garry wrote:
> On 30/10/2015 13:53, Arnd Bergmann wrote:
>> On Monday 26 October 2015 22:14:58 John Garry wrote:
>>
>>> +       /*
>>> +       * DMA-map SMP request, response buffers
>>> +       */
>>> +       /* req */
>>> +       sg_req = &task->smp_task.smp_req;
>>> +       elem = dma_map_sg(dev, sg_req, 1, DMA_TO_DEVICE);
>>> +       if (!elem)
>>> +               return -ENOMEM;
>>> +       req_len = sg_dma_len(sg_req);
>>> +       req_dma_addr = sg_dma_address(sg_req);
>>
>> If you only use the first element, could you just use dma_map_single()?
>>
>
> Can do. Actually sg_req seems only ever has one element:
> expander.c, smp_execute_task()
> sg_init_one(&task->smp_task.smp_req, req, req_size);
>
>
I tried replacing with dma_map_single, but I feel the code is not as 
clean as I need to manually set sg_dma_len() and sg_dma_address():
     req_len = sg_dma_len(sg_req) = sg_req->length;
     sg_dma_address(sg_req) = dma_map_single(dev, sg_virt(sg_req),
  					 req_len, DMA_TO_DEVICE);
     if (dma_mapping_error(dev, sg_dma_address(sg_req)))
          return -ENOMEM;
sg_dma_address(sg_req) is used in another function for unmap.

opinion?
>
>
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> linuxarm@huawei.com
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>
> .
>


cheers,
John