Re: [PATCH] spi: sh-msiof: Update calculation of frequency dividing

[Nobuhiro Iwamatsu <nobuhiro.iwamatsu.yj@renesas.com>]

Hi,

Thanks for your review.

(2015/01/14 17:36), Geert Uytterhoeven wrote:
> Hi Iwamatsu-san,
>
> On Wed, Jan 14, 2015 at 8:25 AM, Nobuhiro Iwamatsu
> <nobuhiro.iwamatsu.yj@renesas.com>  wrote:
>> sh-msiof of frequency dividing does not perform the calculation, driver have
>> to manage setting value in the table. It is not possible to set frequency
>> dividing value close to the actual data in this way. This changes from
>> frequency dividing of table management to setting by calculation.
>> This driver is able to set a value close to the actual data.
>
> Thanks for your patch!
>
>> diff --git a/drivers/spi/spi-sh-msiof.c b/drivers/spi/spi-sh-msiof.c
>> index 96a5fc0..58b1bfe 100644
>> --- a/drivers/spi/spi-sh-msiof.c
>> +++ b/drivers/spi/spi-sh-msiof.c
>> @@ -241,42 +241,37 @@ static irqreturn_t sh_msiof_spi_irq(int irq, void *data)
>>
>>   static struct {
>>          unsigned short div;
>> -       unsigned short scr;
>> -} const sh_msiof_spi_clk_table[] = {
>> -       { 1,    SCR_BRPS( 1) | SCR_BRDV_DIV_1 },
>> -       { 2,    SCR_BRPS( 1) | SCR_BRDV_DIV_2 },
>> -       { 4,    SCR_BRPS( 1) | SCR_BRDV_DIV_4 },
>> -       { 8,    SCR_BRPS( 1) | SCR_BRDV_DIV_8 },
>> -       { 16,   SCR_BRPS( 1) | SCR_BRDV_DIV_16 },
>> -       { 32,   SCR_BRPS( 1) | SCR_BRDV_DIV_32 },
>> -       { 64,   SCR_BRPS(32) | SCR_BRDV_DIV_2 },
>> -       { 128,  SCR_BRPS(32) | SCR_BRDV_DIV_4 },
>> -       { 256,  SCR_BRPS(32) | SCR_BRDV_DIV_8 },
>> -       { 512,  SCR_BRPS(32) | SCR_BRDV_DIV_16 },
>> -       { 1024, SCR_BRPS(32) | SCR_BRDV_DIV_32 },
>> +       unsigned short brdv;
>> +} const sh_msiof_spi_div_table[] = {
>> +       { 1,    SCR_BRDV_DIV_1 },
>> +       { 2,    SCR_BRDV_DIV_2 },
>> +       { 4,    SCR_BRDV_DIV_4 },
>> +       { 8,    SCR_BRDV_DIV_8 },
>> +       { 16,   SCR_BRDV_DIV_16 },
>> +       { 32,   SCR_BRDV_DIV_32 },
>>   };
>>
>>   static void sh_msiof_spi_set_clk_regs(struct sh_msiof_spi_priv *p,
>>                                        unsigned long parent_rate, u32 spi_hz)
>>   {
>>          unsigned long div = 1024;
>> +       unsigned long brps, scr;
>
> "u32", as these are (parts of) 32-bit register values.
>

I see. I will fix.

>>          size_t k;
>>
>>          if (!WARN_ON(!spi_hz || !parent_rate))
>>                  div = DIV_ROUND_UP(parent_rate, spi_hz);
>>
>> -       /* TODO: make more fine grained */
>> -
>> -       for (k = 0; k<  ARRAY_SIZE(sh_msiof_spi_clk_table); k++) {
>> -               if (sh_msiof_spi_clk_table[k].div>= div)
>> -                       break;
>> +       for (k = 0; k<  ARRAY_SIZE(sh_msiof_spi_div_table); k++) {
>> +               brps = DIV_ROUND_UP(div, sh_msiof_spi_div_table[k].div);
>> +               if (brps>  32) /* max of brsv is 32 */
>
> max of brdv

Thanks, I will fix.

>
>> +                       continue;
>> +               break;
>
> Having a conditional "continue" followed by a "break" looks strange.
>
>          if (brps<= 32) /* max of brdv is 32 */
>                  break
>

OK, I will fix this.
>>          }
>
> "brps" may be larger than 32 after the loop.
> In the old code, the min_t() below handled that case.
>

Yes, and div is equal to or higher than 1024, this calculation does not work correctly.
This is the specifications of the device. If div is more than 1024, to add the process
of this function returns error.

>> -       k = min_t(int, k, ARRAY_SIZE(sh_msiof_spi_clk_table) - 1);
>> -
>> -       sh_msiof_write(p, TSCR, sh_msiof_spi_clk_table[k].scr);
>> +       scr = sh_msiof_spi_div_table[k].brdv | (brps -1)<<  8;
>
> "scr = sh_msiof_spi_div_table[k].brdv | SCR_BRPS(i);" would avoid the need
> for "- 1" and the hardcoded shift.
>

I see. I change to using SCR_BRPS(i).

>> +       sh_msiof_write(p, TSCR, scr);
>>          if (!(p->chipdata->master_flags&  SPI_MASTER_MUST_TX))
>> -               sh_msiof_write(p, RSCR, sh_msiof_spi_clk_table[k].scr);
>> +               sh_msiof_write(p, RSCR, scr);
>>   }
>
> Gr{oetje,eeting}s,
>
>                          Geert
>

Best regards,
   Nobuhiro