linux-kernel - Re: [PATCH 2/2] staging: comedi: drivers: usbduxfast.c: fix for DMA buffers on stack

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Message-ID: <512906BF.5030308@bfs.de>
Date:	Sat, 23 Feb 2013 19:13:19 +0100
From:	walter harms <wharms@....de>
To:	Dan Carpenter <dan.carpenter@...cle.com>
CC:	Greg KH <gregkh@...uxfoundation.org>,
	Kumar Amit Mehta <gmate.amit@...il.com>,
	devel@...verdev.osuosl.org, kernel-janitors@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] staging: comedi: drivers: usbduxfast.c: fix for DMA
 buffers on stack



Am 23.02.2013 18:34, schrieb Dan Carpenter:
> On Sat, Feb 23, 2013 at 04:59:43PM +0100, walter harms wrote:
>>>> or is it possible to pass one byte
>>>> in a register ? (aka char/int) without allocating ?
>>>
>>> Nope, the USB host controllers must be able to DMA to this memory
>>> location, so you have to allocate it dynamically, sorry.
>>>
>>> thanks,
>>
>> thx for clarification.
>>
>> @Kumar Amit Mehta:
>> Would you mind to add this as comment ? Allocating one byte does not
>> look clever so maybe will come up with the idea of changing that.
>>
> 
> That can't happen.  The reason is already recorded in the git
> history.  Greg and Ian know that DMA to stack memory doesn't work.
> Most maintainers know about that.  If someone changed it back then
> Fengguang would send an automatic email about it as soon as it was
> committed to a public git tree.
> 

I am not sure about that we talk about the same thing, i am thinking
about the "casual "reader" discovering a one-byte-malloc.
He will not check the githistory, he will thing "WTF there are doing here ?"

I will not make things more complicated, IMHO an malloc of one byte
is a strange thing and strange things should be commented in code.
If the maintainer says "no" i will survive.

re,
 wh

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