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

[Jaehoon Chung]

On 12/16/2012 02:18 AM, Simon Glass wrote:
> Hi,
> 
> On Fri, Nov 30, 2012 at 3:13 PM, Simon Glass <sjg at chromium.org> wrote:
>> 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;
>>>>  }
>>
> 
> Does this patch look good now? I am wondering if it will be including
> in release, or in next?
Well, concept is very good. But i didn't see the any benefit yet.
I will test more...and share the result.

Best Regards,
Jaehoon Chung
> 
> Regards,
> Simon
> 
>> [snip]
>>
>> Regards,
>> Simon
>