Re: [PATCH 05/04] *** NOT FOR RELEASE *** HACK *** Work around MII clock issue ***

[Wolfgang Grandegger <wg@grandegger.com>]

Wolfgang Denk wrote:
> Dear John,
> 
> in message <4b73d43f0906061708o763409d0u10a344dfc30e32c1@mail.gmail.com> you wrote:
>>> The big question seems to be what the RefMan means when talking about
>>> the "system clock frequency". Obiously it is NOT  the  CPU  clock  as
> ...
>>> But which one is it?
>> My best guess is still that it is ips clock.  I think I stated in a previous
>> email ipb, but I meant ips.  5200 has ibp and 5121 has ips.  Have you looked
>> at he MII clock on a scope to see how the calculated values compare to
>> actual?
> 
> Yes, it seems very much as if you were right again.
> 
> When using ips/ibp everything makes sense, and works.
> 
> Hm... so that means on MPC512x we should use mpc512x_find_ips_freq(),
> while on MPC5200 we should use  mpc52xx_find_ipb_freq()  -  but  hey,
> apart from the name these two functions are identical.
> 
> Grant - how would you like to see this handled? Should we merge these
> two code-wise identical functions into one?  What should be the name,
> and in which file should we put it?
> 
> [We need this clock thing for "drivers/net/fs_enet/mii-fec.c"...]

I2C and MSCAN need it as well. What about implementing the more generic
clk api for the MPC5200 as done for the MPC512x?

http://lxr.linux.no/linux+v2.6.29/arch/powerpc/platforms/512x/clock.c

The MSCAN can also operate with other clock sources, e.g. the external
oscillator (ref_clk). This would avoid cumbersome frequency calculations
from the clock bit settings in the driver as shown below:

  /*
   * Get the frequency of the external oscillator clock connected
   * to the SYS_XTAL_IN pin, or retrun 0 if it cannot be determined.
   */
  static unsigned int  __devinit mpc52xx_can_xtal_freq(struct device_node *np)
  {
        struct mpc52xx_cdm  __iomem *cdm;
        struct device_node *np_cdm;
        unsigned int freq;
        u32 val;

        freq = mpc52xx_find_ipb_freq(np);
        if (!freq)
                return 0;

        /*
         * Detemine SYS_XTAL_IN frequency from the clock domain settings
         */
        np_cdm = of_find_matching_node(NULL, mpc52xx_cdm_ids);
        cdm = of_iomap(np_cdm, 0);
        of_node_put(np_cdm);
        if (!np_cdm) {
                printk(KERN_ERR "%s() failed abnormally\n", __func__);
                return 0;
        }

        if (in_8(&cdm->ipb_clk_sel) & 0x1)
                freq *= 2;
        val  = in_be32(&cdm->rstcfg);
        if (val & (1 << 5))
                freq *= 8;
        else
                freq *= 4;
        if (val & (1 << 6))
                freq /= 12;
        else
                freq /= 16;

        iounmap(cdm);

        return freq;
  }

Wolfgang.