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

[Ziyuan Xu <xzy.xu@rock-chips.com>]

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.
>
> 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);
>>>>
>>>
>>>
>>
>>
>>
>>
>
>
>