[U-Boot] [PATCH v2] mmc: Split device init to decouple OCR-polling delay

[Simon Glass]

Hi Jaehoon,

On Fri, Nov 30, 2012 at 12:25 AM, Jaehoon Chung <jh80.chung at samsung.com> wrote:
> Hi,
>
> This concept is very good.
> But I have one question. I think need to call mmc_init() one more, right?
> how did you save the boot time(200ms)?
>
> On 11/29/2012 10:21 AM, Simon Glass wrote:
>> From: Che-Liang Chiou <clchiou at chromium.org>
>>
>> Most of time that MMC driver spends on initializing a device is polling
>> OCR (operation conditions register).  To decouple this polling loop,
>> device init is split into two parts: The first part fires the OCR query
>> command, and the second part polls the result.  So the caller is now no
>> longer bound to the OCR-polling delay; he may fire the query, go
>> somewhere and then come back later for the result.
>>
>> To use this, call mmc_set_preinit() on any device which needs this.
>>
>> This can save significant amounts of time on boot (e.g. 200ms) by
>> hiding the MMC init time behind other init.
> snip..
>> +int mmc_init(struct mmc *mmc)
>> +{
>> +     int err = IN_PROGRESS;
>> +     unsigned start = get_timer(0);
>> +
>> +     if (mmc->has_init)
>> +             return 0;
>> +     if (!mmc->init_in_progress)
>> +             err = mmc_start_init(mmc);
> It need not to return? if err is IN_PROGRESS, next condition is immediately run.
> Then i think we didn't save the time before adjust this patch.

It's a little confusing, but the way it works is that mmc_preinit()
calls mmc_start_init() early in boot. Then when mmc_init() finally
gets called (later) it finishes off the init. We still need mmc_init()
to actually fully complete the init. If it were to return before
completing the init then we would be unable to use the MMC.

>> +
>> +     if (!err || err == IN_PROGRESS)
>> +             err = mmc_complete_init(mmc);
>> +     debug("%s: %d, time %lu\n", __func__, err, get_timer(start));
>>       return err;
>>  }

[snip]

Regards,
Simon