[U-Boot] [PATCH] mmc: dw_mmc: reduce timeout detection cycle

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

Hi,

On 07/19/2016 04:40 PM, Ziyuan Xu wrote:
> Hi Jaehoon,
> 
> On 2016?07?19? 12:22, Jaehoon Chung wrote:
>> Hi Ziyuan,
>>
>> On 07/19/2016 11:33 AM, Ziyuan Xu wrote:
>>> Hi Jaehoon,
>>>
>>> On 2016?07?19? 10:03, Jaehoon Chung wrote:
>>>> Hi Ziyuan,
>>>>
>>>> On 07/19/2016 10:38 AM, Ziyuan Xu wrote:
>>>>> It's no need to speed 10 seconds to wait the mmc device out from busy
>>>>> status. 500 milliseconds enough.
>>>> I agreed that 10 seconds is too big..
>>>> Could you explain more how you get 500ms and feel enough?
>>> Ordinarily, there are 3 types of scenarios that the mmc device was busy:
>>> 1. The mmc interface didn't initialize (eg. gpio  iomux)
>>> The device will be busy status until gpio iomux.
>>>
>>> 2. The last command with data transfer.
>>> The maximum value of data timeout is 0xffffff cyles(see dwi databook Timeout Register), and the clock is up to 52MHZ under high speed mode.
>>> timeout = 0xffffff * 1/52M = 0.32s
>>>
>>> 3. voltage switch
>>> U-BOOT doesn't support voltage switch.
>>>
>>> In summary, I think 500 milliseconds is enough. What do you think?
>> I think it's not important thing.
>>
>> This is for checking whether card is busy or not before sending command.
>> I think it's not relevant to Timeout register. Just ensure that card is not busy before sending command.
>> And there is no effect for I/O performance, isn't?
> Yup,  I agree with you.  For scenarios 2, I mean that if the last command with data transfer, we will hit data_busy assertion probably. If the mmc device remains in a busy state more than 500ms, I think it may also be busy state after 10s.
>>
>> But 50ms is not bad. :) It's personal preference.
> BTW, the timeout value is 500ms in kernel.

Yep, it looks good to me. :)
I have tested your patch with Exynos SoCs.

Reviewed-by: Jaehoon Chung <jh80.chung@samsung.com>
Tested-by: Jaehoon Chung <jh80.chung@samsung.com>

Best Regards,
Jaehoon Chung

>>
>> Best Regards,
>> Jaehoon Chung
>>
>>>> Best Regards,
>>>> Jaehoon Chung
>>>>
>>>>> Signed-off-by: Ziyuan Xu <xzy.xu@rock-chips.com>
>>>>> ---
>>>>>
>>>>>    drivers/mmc/dw_mmc.c | 2 +-
>>>>>    1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/drivers/mmc/dw_mmc.c b/drivers/mmc/dw_mmc.c
>>>>> index 2cf7bae..790a166 100644
>>>>> --- a/drivers/mmc/dw_mmc.c
>>>>> +++ b/drivers/mmc/dw_mmc.c
>>>>> @@ -195,7 +195,7 @@ static int dwmci_send_cmd(struct mmc *mmc, struct mmc_cmd *cmd,
>>>>>        ALLOC_CACHE_ALIGN_BUFFER(struct dwmci_idmac, cur_idmac,
>>>>>                     data ? DIV_ROUND_UP(data->blocks, 8) : 0);
>>>>>        int ret = 0, flags = 0, i;
>>>>> -    unsigned int timeout = 100000;
>>>>> +    unsigned int timeout = 500;
>>>>>        u32 retry = 100000;
>>>>>        u32 mask, ctrl;
>>>>>        ulong start = get_timer(0);
>>>>>
>>>>
>>>>
>>>
>>>
>>>
>>>
>>
>>
>>
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