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

From: Ulf Hansson
Date: Tue May 15 2012 - 03:16:46 EST

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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