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

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Date:	Mon, 02 Nov 2015 21:29:50 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	John Garry <john.garry@...wei.com>
Cc:	mark.rutland@....com, devicetree@...r.kernel.org,
	linux-scsi@...r.kernel.org, pawel.moll@....com,
	ijc+devicetree@...lion.org.uk, JBottomley@...n.com,
	john.garry2@...l.dcu.ie, linux-kernel@...r.kernel.org,
	linuxarm@...wei.com, robh+dt@...nel.org, hare@...e.de,
	galak@...eaurora.org, zhangfei.gao@...aro.org
Subject: Re: [PATCH v2 27/32] scsi: hisi_sas: add smp protocol support

On Monday 02 November 2015 17:03:58 John Garry wrote:
> >
> > 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?
> 

What I meant was not using a struct scatterlist at all:
replace the 'sg_req' variable with a normal pointer, and then
do

	hdr->cmd_table_addr = cpu_to_le64(dma_map_single(dev, req, len, DMA_TO_DEVICE));

Any reason this won't work?

	Arnd
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