Subject: [PATCH 1/1] ARM iMX28: incorrect frac/div calculation

From: [email-masked] (Matt Burtch)
Date: Fri, 23 Mar 2012 11:38:58 -0700

On 03/23/2012 12:13 AM, Lothar Wa?mann wrote:
> Hi,
>
> Matt Burtch writes:
>> The frac and div values in _CLK_SET_RATE are calculated incorrectly
>> for some clock rates ie. CPU clk of 454.73MHz, 392.72MHz, 261.81Mhz,
>> etc.
>>
>> Now the frac and div values which result in the closest actual clock
>> rate to that requested is selected.  Also there are no limitations
>> on what frac values can be used, as long as they fall in the valid
>> (18<  frac<  35) range.
>>
>> Tested on custom iMX28 board.
>>
>> Signed-off-by: Matt Burtch<[email-masked]>
>> ---
>>   arch/arm/mach-mxs/clock-mx28.c |    8 ++------
>>   1 files changed, 2 insertions(+), 6 deletions(-)
>>
>> diff --git a/arch/arm/mach-mxs/clock-mx28.c b/arch/arm/mach-mxs/clock-mx28.c
>> index 5d68e41..a058b99 100644
>> --- a/arch/arm/mach-mxs/clock-mx28.c
>> +++ b/arch/arm/mach-mxs/clock-mx28.c
>> @@ -354,19 +354,15 @@ static int name##_set_rate(struct clk *clk, unsigned long rate)		\
>>   		}							\
>>   		for (d = 1; d<= div_max; d++) {			\
>>   			f = parent_rate * 18 / d / rate;		\
>> -			if ((parent_rate * 18 / d) % rate)		\
>> -				f++;					\
>>   			if (f<  18 || f>  35)				\
>>   				continue;				\
>>   									\
>>   			calc_rate = parent_rate * 18 / f / d;		\
>> -			if (calc_rate>  rate)				\
>> -				continue;				\
>>   									\
>> -			if (rate - calc_rate<  diff) {			\
>> +			if (abs(rate - calc_rate)<  diff) {		\
> Shouldn't this actually be '<=' (also in the original code)?
Hi Lothar,

It shouldn't make a difference. If it was '<=' it would result in a 
different frac and higher div value but the difference between the 
requested rate and actual would be the same.

Thanks,
Matt Burtch
> Lothar Wa?mann