linux-kernel - Re: [PATCH] mmc:sdio:retry CMD52/53 when error happens

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Date:	Tue, 15 May 2012 09:15:42 +0200
From:	Ulf Hansson <ulf.hansson@...ricsson.com>
To:	Yong Ding <yongd@...vell.com>
Cc:	"cjb@...top.org" <cjb@...top.org>,
	"linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
	"stefan.xk.nilsson@...ricsson.com" <stefan.xk.nilsson@...ricsson.com>,
	"linus.walleij@...aro.org" <linus.walleij@...aro.org>,
	"svenkatr@...com" <svenkatr@...com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mmc:sdio:retry CMD52/53 when error happens

Hi Yong Ding,

On 05/15/2012 05:14 AM, Yong Ding wrote:
> Hi Ulf Hansson, Thanks for your comments.
>
> Such retry mechanism is a simple CMD-level or sdio-core-level retry
> which takes advantage of the mmc core internal retry. There is not
> any side effect, but with it, even those SDIO function driver's
> without its own retrying mechanism can benefit in some conditions.

I am not sure about that. It all depends on what kind of protocol the 
SDIO func driver is handling and as well what SDIO hw that is connected.

For a WLAN interface you might end up in reading/writing the next 
buffer, maybe messing up even more data. Have you considered this?

>
> Besides, for CMD52, it can be used during SDIO card
> initialization/detection phase. At that time, SDIO function driver
> hasn't started to work. Of course we can probably encounter CMD52
> error due to some reasons(eg, board-level schematic bad behavior),
> and such retry can be a potential workaround. Actually, we've
> encountered exactly such case in our development.

I realize that there is a need for this, but I am not sure we always 
would like to have "retries" for every CMD52/53 request.

During SDIO initialization before SDIO func driver is started, retries 
should be safe since there is no upper protocol to consider yet. Maybe 
we should try to create a patch which only enables retries during SDIO 
init sequence instead!?

Kind regards
Ulf Hansson
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