[U-Boot] [PATCH] mmc: retry the cmd8 to meet 74 clocks requirement in the spec

[Lei Wen <adrian.wenl@gmail.com>]

Hi Andy,

On Mon, Sep 5, 2011 at 6:45 AM, Andy Fleming <afleming@gmail.com> wrote:
> On Sun, Sep 4, 2011 at 5:18 PM, Marek Vasut <marek.vasut@gmail.com> wrote:
>> On Saturday, September 03, 2011 05:34:17 AM Lei Wen wrote:
>>> For some controller it has dynamic clock gating, and only toggle out clk
>>> when the first cmd0 send out, while some card strictly obey the 74
>>> clocks rule, the interval may not be sufficient between the cmd0 and
>>> this cmd8, retry to fulfil the clock requirement.
>
>
> This seems like the wrong way to handle this. What if another
> controller shows up, but it takes *4* retries. Or *5*?
>
> Or *100*? This sort of knowledge should somehow be embedded in either
> the driver for that controller, or the board
> code. Not the generic MMC code.
>
> Maybe put it in the init code for the controller?
>

The card after the cmd0 need sometimes to be stabilize. Linux also add
some kind of
mmc_delay function inside the mmc_go_idle() fucntion in the generic framework.

The retry time cannot be 100 that much. :) Since the 74 clocks is such
short time, that
even the second try would serve good. Make it a part of generic could
remove the ugly
handling in the controller driver itself, and others also could
benefit from it...

Best regards,
Lei