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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>
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Date: Fri, 30 Oct 2015 16:22:53 +0000
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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);

>> +       hdr->cmd_table_addr_lo = cpu_to_le32(lower_32_bits(req_dma_addr));
>> +       hdr->cmd_table_addr_hi = cpu_to_le32(upper_32_bits(req_dma_addr));
>> +
>> +       hdr->sts_buffer_addr_lo =
>> +                       cpu_to_le32(lower_32_bits(slot->status_buffer_dma));
>> +       hdr->sts_buffer_addr_hi =
>> +                       cpu_to_le32(upper_32_bits(slot->status_buffer_dma));
>> +
>>
>
> I see these a lot in your code. Could you replace this wit
>
> 	hdr->cmd_table_addr = cpu_to_le64(req_dma_addr);
>
This seems reasonable. They are not swapped.

> and so on? That would be much more readable. Or are the two __le32 variables
> swapped? If so, you could add a small helper function like
>
> static inline __le64 cpu_to_le64_wordswapped(u64 val)
> {
> 	return cpu_to_le64(val >> 32 | val << 32);
> }
>
> 	Arnd
>
> .
>

cheers