Re: [PATCH 2/2] mmc: sh_mmcif: mmc->f_max should be half of the bus clock

[Yusuke Goda <yusuke.goda.sx@renesas.com>]

Hi Simon-san

(2012/03/26 14:52), Simon Horman wrote:
> On Mon, Mar 26, 2012 at 02:45:30PM +0900, Yusuke Goda wrote:
>> Hi Simon-san, Guennadi-san
>>
>> (2012/03/26 7:30), Simon Horman wrote:
>>> On Sat, Mar 24, 2012 at 07:06:31PM +0100, Guennadi Liakhovetski wrote:
>>>> On Wed, 21 Mar 2012, Simon Horman wrote:
>>>>
>>>>> mmc->f_max should be half of the bus clock.
>>>>> And now that mmc->f_max is not equal to the bus clock the
>>>>> latter should be used directly to calculate mmc->f_min.
>>>>
>>>> The patch seems correct as it stands, however, looking at it - does anyone 
>>>> understands why that "close to 400kHz" comment and such a complicated 
>>>> calculation? Shouldn't it be just host->clk / 512 always? Maybe this 
>>>> should be a separate patch, so, for this one
>>>>
>>>> Acked-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
>>>
>>> Hi Guennadi,
>>>
>>> that code seems to date back to the original driver submission
>>> made by Goda-san. I have CCed him as perhaps he recalls why
>>> the code is like it is.
>> I thought to get closer to 400kHz if possible.
>> Probably even host->clk / 512 does not have any problem.
> 
> Sorry for my ignorance, is ~400kHz desirable for some reason?
Initialization time becomes short.

Thanks
Goda


>>>>> Cc: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
>>>>> Tested-by: Cao Minh Hiep <hiepcm@gmail.com>
>>>>> Signed-off-by: Simon Horman <horms@verge.net.au>
>>>>> ---
>>>>>  drivers/mmc/host/sh_mmcif.c |   12 ++++++------
>>>>>  1 files changed, 6 insertions(+), 6 deletions(-)
>>>>>
>>>>> diff --git a/drivers/mmc/host/sh_mmcif.c b/drivers/mmc/host/sh_mmcif.c
>>>>> index 5014bc4..1410baa 100644
>>>>> --- a/drivers/mmc/host/sh_mmcif.c
>>>>> +++ b/drivers/mmc/host/sh_mmcif.c
>>>>> @@ -1297,14 +1297,14 @@ static int __devinit sh_mmcif_probe(struct platform_device *pdev)
>>>>>  	spin_lock_init(&host->lock);
>>>>>  
>>>>>  	mmc->ops = &sh_mmcif_ops;
>>>>> -	mmc->f_max = host->clk;
>>>>> +	mmc->f_max = host->clk / 2;
>>>>>  	/* close to 400KHz */
>>>>> -	if (mmc->f_max < 51200000)
>>>>> -		mmc->f_min = mmc->f_max / 128;
>>>>> -	else if (mmc->f_max < 102400000)
>>>>> -		mmc->f_min = mmc->f_max / 256;
>>>>> +	if (host->clk < 51200000)
>>>>> +		mmc->f_min = host->clk / 128;
>>>>> +	else if (host->clk < 102400000)
>>>>> +		mmc->f_min = host->clk / 256;
>>>>>  	else
>>>>> -		mmc->f_min = mmc->f_max / 512;
>>>>> +		mmc->f_min = host->clk / 512;
>>>>>  	if (pd->ocr)
>>>>>  		mmc->ocr_avail = pd->ocr;
>>>>>  	mmc->caps = MMC_CAP_MMC_HIGHSPEED;
>>>>> -- 
>>>>> 1.7.6.3
>>>>>
>>>>
>>>> ---
>>>> Guennadi Liakhovetski, Ph.D.
>>>> Freelance Open-Source Software Developer
>>>> http://www.open-technology.de/
>>>>
>>>
>>>
>>