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

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Message-ID: <56389DA6.6070103@huawei.com>
Date:	Tue, 3 Nov 2015 11:42:30 +0000
From:	John Garry <john.garry@...wei.com>
To:	Arnd Bergmann <arnd@...db.de>
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 02/11/2015 20:29, Arnd Bergmann wrote:
> 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
>
> .
>
There seems to be some misunderstanding. Are you suggesting I change 
sas_smp_task?
./include/scsi/libsas.h
struct sas_smp_task {
	struct scatterlist smp_req;
	struct scatterlist smp_resp;
};

thanks,
John

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