Re: use default speed of the eMMC

[Jaehoon Chung <jh80.chung@samsung.com>]

On 05/26/2016 03:34 PM, 장민우 wrote:
> Yes, "default speed mode" what I mentioned is using below 26MHz clock
> (not in high speed mode).
> 
> While eMMC card is on the initializing step, it uses below 400KHz not 26MHz.
> 
> I just want to use below 26MHz, because some customers want to use low
> hertz clock.

Just for some customers? Then You can add the workaround code in your local.

> 
> So, eMMC versions and environments have nothing to do with "default speed mode".

How do you set your "default speed mode"? (Support HS/DDR/HS200 etc..)

It seems that can't set the lower hertz than 26MHz with only your patch.
what hertz exactly? Your purpose is just hook for some customers.

And i can't find "default speed mode" in eMMC SPEC. Could you explain where mentioned "default speed mode"?

Best Regards,
Jaehoon Chung

> 
> If there is a misunderstanding, please let me know.
> 
> Thank you.
> 
> Best Regards,
> Minwoo Jang
> 
> 
> 2016-05-26 14:49 GMT+09:00 Jaehoon Chung <jh80.chung@samsung.com>:
>> On 05/26/2016 02:16 PM, 장민우 wrote:
>>> Hello, Jaehoon Chung.
>>>
>>> I mentioned "default speed mode" not hs200, hs400, ddr and hs mode.
>>
>> Yes, default speed mode is not HS400, HS400, DDR..
>> You mean "default speed mode" is 26MHz?
>>
>> As i know, default speed is 26MHz. and it used for initializing card.
>>
>>>
>>> I think If "default speed mode" is set, there is no bus width change.
>>
>> There is DEVICE_TYPE[196] at ext_csd register.
>> Device type should be selected one of them. (You can see the currently valid value.)
>>
>> I don't know exactly what your purpose.
>> If i missed something, let me know in more detail about default speed, eMMC version, your environment.
>>
>> Best Regards,
>> Jaehoon Chung
>>
>>>
>>> If you have any advice to use "default speed mode" of the eMMC. please
>>> let me know.
>>>
>>> Thank you.
>>>
>>> Best Regards,
>>> Minwoo Jang.
>>>
>>> 2016-05-24 18:41 GMT+09:00 Jaehoon Chung <jh80.chung@samsung.com>:
>>>> Hi,
>>>>
>>>> On 05/24/2016 06:07 PM, 장민우 wrote:
>>>>> Dear linux-mmc.
>>>>>
>>>>> Hello, I'm Minwoo Jang.
>>>>>
>>>>> I have a question about using default speed of the eMMC.
>>>>>
>>>>> When default speed is used, mmc_select_bus_width() is never called.
>>>>>
>>>>> So, eMMC can not be set 4 bit or 8 bit bus width, I think.
>>>>>
>>>>> Please, give me your opinions on the following diff codes.
>>>>
>>>> In mmc_select_timing(), timing should be set to MMC_TIMING_HS or others.
>>>> Then mmc_select_bus_width() should be entered.
>>>>
>>>> Best Regards,
>>>> Jaehoon Chung
>>>>
>>>>>
>>>>> Thank you.
>>>>>
>>>>> =====================================================
>>>>>
>>>>> diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
>>>>> index 94b4462..3b1cc4d 100644
>>>>> --- a/drivers/mmc/core/mmc.c
>>>>> +++ b/drivers/mmc/core/mmc.c
>>>>> @@ -952,6 +952,8 @@ static int mmc_select_bus_width(struct mmc_card *card)
>>>>>
>>>>>                 if (!err) {
>>>>>                         err = bus_width;
>>>>> +                       pr_warn("%s: switch to bus width %d\n",
>>>>> +                               mmc_hostname(host), (1 << bus_width));
>>>>>                         break;
>>>>>                 } else {
>>>>>                         pr_warn("%s: switch to bus width %d failed\n",
>>>>> @@ -1500,6 +1502,14 @@ static int mmc_init_card(struct mmc_host *host, u32 ocr,
>>>>>                         if (err)
>>>>>                                 goto err;
>>>>>                 }
>>>>> +       } else {
>>>>> +               /* Select the bus width for normal speed mode */
>>>>> +               err = mmc_select_bus_width(card);
>>>>> +               if (IS_ERR_VALUE(err)) {
>>>>> +                       pr_warn("%s: Selecting bus width failed\n",
>>>>> +                               mmc_hostname(card->host));
>>>>> +                       goto err;
>>>>> +               }
>>>>>         }
>>>>>
>>>>> Best regards,
>>>>>
>>>>> MW Jang.
>>>>> --
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>>>>>
>>>>>
>>>>
>>>
>>>
>>>
>>
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