[U-Boot] [PATCH v2] spi: mxc_spi: Update pre and post divider algorithm

[Stefano Babic <sbabic@denx.de>]

Hi Dirk,

On 12/06/2013 07:28, Dirk Behme wrote:
> On 11.05.2013 07:25, Dirk Behme wrote:
>> The spi clock divisor is of the form x * (2**y),  or  x  << y, where x is
>> 1 to 16, and y is 0 to 15. Note the similarity with floating point
>> numbers.
>> Convert the desired divisor to the smallest number which is >= desired
>> divisor,
>> and can be represented in this form. The previous algorithm chose a
>> divisor
>> which could be almost twice as large as needed.
>>
>> Signed-off-by: Troy Kisky <troy.kisky@boundarydevices.com>
>> Signed-off-by: Dirk Behme <dirk.behme@gmail.com>
> 
> While we are talking about a first -rc now, could we get these two patches
> 
> http://patchwork.ozlabs.org/patch/242709/
> 
> http://patchwork.ozlabs.org/patch/243113/

Sorry to come late with these two patches - after a first glance when
you post then, I put the patches at the bottom of my queue and I never
checked again.

I will work them before end of the week.

Best regards,
Stefano Babic


> 
> applied?
> 
> Thanks
> 
> Dirk
> 
>> ---
>>
>> Notes:
>>
>> - Changes in v2: Make the alogrithm simpler by removing the -1 as
>> proposed
>>                   by Troy. Make the pre_div and post_div u32.
>>
>> - This replaces v1 of this patch and depends on the previous sent patch
>>    http://patchwork.ozlabs.org/patch/242709/
>>
>>   drivers/spi/mxc_spi.c |   30 ++++++++++++------------------
>>   1 file changed, 12 insertions(+), 18 deletions(-)
>>
>> diff --git a/drivers/spi/mxc_spi.c b/drivers/spi/mxc_spi.c
>> index 3e903b3..e87b899 100644
>> --- a/drivers/spi/mxc_spi.c
>> +++ b/drivers/spi/mxc_spi.c
>> @@ -128,8 +128,8 @@ static s32 spi_cfg_mxc(struct mxc_spi_slave *mxcs,
>> unsigned int cs,
>>           unsigned int max_hz, unsigned int mode)
>>   {
>>       u32 clk_src = mxc_get_clock(MXC_CSPI_CLK);
>> -    s32 pre_div = 1, post_div = 0, i, reg_ctrl, reg_config;
>> -    u32 ss_pol = 0, sclkpol = 0, sclkpha = 0;
>> +    s32 reg_ctrl, reg_config;
>> +    u32 ss_pol = 0, sclkpol = 0, sclkpha = 0, pre_div = 0, post_div = 0;
>>       struct cspi_regs *regs = (struct cspi_regs *)mxcs->base;
>>
>>       if (max_hz == 0) {
>> @@ -147,26 +147,20 @@ static s32 spi_cfg_mxc(struct mxc_spi_slave
>> *mxcs, unsigned int cs,
>>       reg_ctrl |=  MXC_CSPICTRL_EN;
>>       reg_write(&regs->ctrl, reg_ctrl);
>>
>> -    /*
>> -     * The following computation is taken directly from Freescale's
>> code.
>> -     */
>>       if (clk_src > max_hz) {
>> -        pre_div = DIV_ROUND_UP(clk_src, max_hz);
>> -        if (pre_div > 16) {
>> -            post_div = pre_div / 16;
>> -            pre_div = 16;
>> -        }
>> -        if (post_div != 0) {
>> -            for (i = 0; i < 16; i++) {
>> -                if ((1 << i) >= post_div)
>> -                    break;
>> -            }
>> -            if (i == 16) {
>> +        pre_div = (clk_src - 1) / max_hz;
>> +        /* fls(1) = 1, fls(0x80000000) = 32, fls(16) = 5 */
>> +        post_div = fls(pre_div);
>> +        if (post_div > 4) {
>> +            post_div -= 4;
>> +            if (post_div >= 16) {
>>                   printf("Error: no divider for the freq: %d\n",
>>                       max_hz);
>>                   return -1;
>>               }
>> -            post_div = i;
>> +            pre_div >>= post_div;
>> +        } else {
>> +            post_div = 0;
>>           }
>>       }
>>
>> @@ -174,7 +168,7 @@ static s32 spi_cfg_mxc(struct mxc_spi_slave *mxcs,
>> unsigned int cs,
>>       reg_ctrl = (reg_ctrl & ~MXC_CSPICTRL_SELCHAN(3)) |
>>           MXC_CSPICTRL_SELCHAN(cs);
>>       reg_ctrl = (reg_ctrl & ~MXC_CSPICTRL_PREDIV(0x0F)) |
>> -        MXC_CSPICTRL_PREDIV(pre_div - 1);
>> +        MXC_CSPICTRL_PREDIV(pre_div);
>>       reg_ctrl = (reg_ctrl & ~MXC_CSPICTRL_POSTDIV(0x0F)) |
>>           MXC_CSPICTRL_POSTDIV(post_div);
>>
>>
> 
> 
> 


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