Jon Smirl wrote:

For mpc5200 it is easy, mpc52xx_find_ipb_freq()  already exists to get
the source clock for the i2c devices. Each i2c node in the device tree
can then specify "clock-frequency = 400000;" or let it default. You

400KHz is the *speed* of the I2C bus, so let's be sure to use "speed" in the
property name.  Reserve the word "bus" for the input clock to the I2C device.

#if defined(CONFIG_MPC8540) || defined(CONFIG_MPC8541) || \
       defined(CONFIG_MPC8560) || defined(CONFIG_MPC8555)
       gd->i2c1_clk = sys_info.freqSystemBus;
#elif defined(CONFIG_MPC8544)
       /*
        * On the 8544, the I2C clock is the same as the SEC clock.  This can be
        * either CCB/2 or CCB/3, depending on the value of cfg_sec_freq. See
        * 4.4.3.3 of the 8544 RM.  Note that this might actually work for all
        * 85xx, but only the 8544 has cfg_sec_freq, so it's unknown if the
        * PORDEVSR2_SEC_CFG bit is 0 on all 85xx boards that are not an 8544.
        */
       if (gur->pordevsr2 & MPC85xx_PORDEVSR2_SEC_CFG)
               gd->i2c1_clk = sys_info.freqSystemBus / 3;
       else
               gd->i2c1_clk = sys_info.freqSystemBus / 2;
#else
       /* Most 85xx SOCs use CCB/2, so this is the default behavior. */
       gd->i2c1_clk = sys_info.freqSystemBus / 2;
#endif
       gd->i2c2_clk = gd->i2c1_clk;

I think the whole point is to eliminate duplicating this code in the Linux
driver.  It's hideously ugly, so it should be limited as much as possible.

-- 
Timur Tabi
Linux kernel developer at Freescale