linux-kernel - Re: [PATCH V3 3/4] dmaselftest: add memcpy selftest support functions

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Message-ID: <56417772.7050905@codeaurora.org>
Date:	Mon, 9 Nov 2015 23:49:54 -0500
From:	Sinan Kaya <okaya@...eaurora.org>
To:	Timur Tabi <timur@...eaurora.org>, dmaengine@...r.kernel.org,
	cov@...eaurora.org, jcm@...hat.com
Cc:	agross@...eaurora.org, linux-arm-msm@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	Vinod Koul <vinod.koul@...el.com>,
	Dan Williams <dan.j.williams@...el.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH V3 3/4] dmaselftest: add memcpy selftest support functions



On 11/9/2015 8:48 AM, Timur Tabi wrote:
> Sinan Kaya wrote:
>>>
>>> And why kmalloc anyway?  Why not leave it on the stack?
>>>
>>>      char src[] = "hello world";
>>>
>>> ?
>>
>> I need to call dma_map_single on this address to convert it to a DMA
>> address. That's why.
>
> And you can't do that with an object that's on the stack?
>

no, pasting from here.

https://www.kernel.org/doc/Documentation/DMA-API-HOWTO.txt

under 'What memory is DMA'able?'

This rule also means that you may use neither kernel image addresses
(items in data/text/bss segments), nor module image addresses, nor
stack addresses for DMA.

-- 
Sinan Kaya
Qualcomm Technologies, Inc. on behalf of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a 
Linux Foundation Collaborative Project
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