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

[Jagan Teki]

On Wed, Jun 12, 2013 at 9:12 PM, Stefano Babic <sbabic at denx.de> wrote:
> 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 at boundarydevices.com>
>>> Signed-off-by: Dirk Behme <dirk.behme at 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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Sorry, i didn't understand the conversation here, was this fix applied?
Could you please explain.

--
Thanks,
Jagan.