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

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

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?

But 50ms is not bad. :) It's personal preference.

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);
>>>
>>
>>
>>
> 
> 
> 
> 
>