linux-kernel - Re: [PATCH v2 27/32] scsi: hisi

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Date:	Fri, 30 Oct 2015 14:53:51 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	John Garry <john.garry@...wei.com>
Cc:	JBottomley@...n.com, robh+dt@...nel.org, pawel.moll@....com,
	mark.rutland@....com, ijc+devicetree@...lion.org.uk,
	galak@...eaurora.org, linux-scsi@...r.kernel.org,
	linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
	linuxarm@...wei.com, john.garry2@...l.dcu.ie, hare@...e.de,
	xuwei5@...ilicon.com, zhangfei.gao@...aro.org
Subject: Re: [PATCH v2 27/32] scsi: hisi_sas: add smp protocol support

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()?

> +       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);

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
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