PSC clock divider

[Grant Likely]

On Fri, Aug 7, 2009 at 10:03 AM, Jon Smirl<jonsmirl at gmail.com> wrote:
> mpc52xx_set_psc_clkdiv() has problems. It take the clk divider as a
> parameter. But this divisor is not always gettting calculated
> correctly. My code in i2s was doing it wrong.
>
> Take this snippet from the SPI driver, it just assumes a fsystem of
> 512Mhz. fsystem is 533Mhz on my boards.
>
>        /* default sysclk is 512MHz */
>        mclken_div = (mps->sysclk ? mps->sysclk : 512000000) / MCLK;
>        mpc52xx_set_psc_clkdiv(psc_id, mclken_div);
>
> Is it also not accounting for the hardware adding one to the divisor.
>
> I've change i2s to this:
>
>                        if (!fsystem) {
>                                np = of_find_matching_node(NULL, mpc52xx_cdm_ids);
>                                mpc52xx_cdm = of_iomap(np, 0);
>                                fsystem = mpc5xxx_get_bus_frequency(np);
>                                of_node_put(np);
>                                val = in_be32(&mpc52xx_cdm->rstcfg);
>                                if (val & (1 << 5))
>                                        fsystem *= 8;
>                                else
>                                        fsystem *= 4;
>                                iounmap(mpc52xx_cdm);
>                        }
>                        clkdiv = fsystem / freq;
>                        err = fsystem % freq;
>                        if (err > freq / 2)
>                                clkdiv++;
>
>                        dev_dbg(psc_dma->dev, "psc_i2s_set_sysclk(clkdiv %d freq error=%dHz)\n",
>                                        clkdiv, (fsystem / clkdiv - freq));
>
>                        /* PSC is 1-6 */
>                        /* Hardware adds 1 to divisor */
>                        return mpc52xx_set_psc_clkdiv(psc_dma->id + 1, clkdiv - 1);
>
>
> Should I modify mpc52xx_set_psc_clkdiv() to take in a frequency and
> them move this code into mpc52xx_common.c? That allows the sysclk
> parameter to be eliminated for SPI.

Yes, please do.

g.

-- 
Grant Likely, B.Sc., P.Eng.
Secret Lab Technologies Ltd.