linux-kernel - Re: [PATCH] i2c: designware: use {readl|writel}

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:	Wed, 14 Jan 2015 12:05:09 +0800
From:	Jisheng Zhang <jszhang@...vell.com>
To:	Wolfram Sang <wsa@...-dreams.de>
CC:	"linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] i2c: designware: use {readl|writel}_relaxed instead of
 readl/writel

Dear Wolfram,

On Tue, 13 Jan 2015 06:36:54 -0800
Wolfram Sang <wsa@...-dreams.de> wrote:

> 
> On Thu, Dec 11, 2014 at 02:26:41PM +0800, Jisheng Zhang wrote:
> > readl/writel is too expensive especially on Cortex A9 w/ outer L2 cache.
> > This introduces i2c read/write errors on Marvell BG2/BG2Q SoCs when there
> > are heavy L2 cache maintenance operations at the same time.
> 
> Reading this again, I got a question:
> 
> Really read/write errors? I would think that there is a performance
> penalty because of the memory barriers. But errors?

I dunno whether I can call the issue as error. The situation is one i2c client
has a bit strict timing requirement. Without the patch, if there are heavy L2 cache
maintenance operations at the same time, there may be long delay between each
DW_IC_DATA_CMD write opeartions in i2c_dw_xfer_msg() in the DW_IC_INTR_TX_EMPTY isr.

Thus about 1/300 i2c transactions may be ignored by the i2c client per my test.

> 
> > The driver does not perform DMA, so it's safe to use the relaxed version.
> > From another side, the relaxed io accessor macros are available on all
> > architectures now, so we can use the relaxed versions instead.
> 
> Can the designware core make use of DMA in theory?
> 

the IP can do DMA in theory. But currently, there's no DMA support in the driver.

Thanks for your review,
Jisheng
--
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/