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

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

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?

>
> 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);
>>
>
>
>