linux-kernel - Re: [PATCH] dmaengine: add CSR SiRFprimaII DMAC driver

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Sat, 10 Sep 2011 07:37:59 +0800
From:	Barry Song <21cnbao@...il.com>
To:	Vinod Koul <vkoul@...radead.org>
Cc:	vinod.koul@...el.com, "arnd@...db.de" <arnd@...db.de>,
	"linus.walleij@...aro.org" <linus.walleij@...aro.org>,
	Jassi Brar <jassisinghbrar@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"workgroup.linux@....com" <workgroup.linux@....com>,
	"rongjun.ying@....com" <rongjun.ying@....com>,
	"Baohua.Song@....com" <Baohua.Song@....com>,
	"Williams, Dan J" <dan.j.williams@...el.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] dmaengine: add CSR SiRFprimaII DMAC driver

2011/9/10 Vinod Koul <vkoul@...radead.org>:
> On Fri, 2011-09-09 at 10:52 +0800, Barry Song wrote:
>> >
>> > Actually, there is no real case for xlen > dma_width. this picture is
>> > only explaining what will happen if we set xlen > dma_width.
>> > when xlen > dma_width, for every line, dma will transfer only
>> > dma_width. Then the extra data is wrapped around
>> > to the next data line, it will corrupt the DMA transfer for
>> > multiple-line 2-D DMA since the extra data will overlap with the real
>> > next line.
>> >
>> > if we set ylen to 0, the DMA becomes 1D, the wrap-around of the extra
>> > data has no issue nobody will overlap with it.
>> >
>>
>> For example, if we set xlen = 7, dma_width =4, ylen > 0
>> then dma will happen like:
>> 0~6
>> 4~10
>> 8~14
>> 12~18
>> ....
> Is there a real world use case of this??

no real case actually and hardware spec says it is wrong to set xlen >
dma_width since it causes the above overlap.

>
>>
>> But for ylen=0, it has no issue. there is no next line to overlap with
>> the extra data.
>>
>> in case we set xlen = 0, something funny will happen:
>> i will copy the same memory again and again(ylen+1 times).
>
>
> --
> ~Vinod Koul
> Intel Corp.
>
>

Thanks
barry
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/