Grant Likely wrote:
> This is a solved problem. The device tree simple claims compatibility
> with an older part that has the identical register-level interface.
That would assume that the clock frequency is the only thing that decides
compatibility, which may technically be true now, but I don't think it's a good
idea.
I don't understand what's wrong with simply specifying the actual clock
frequency that the device uses? It varies from SOC to SOC, but U-Boot
calculates today already:
#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;
We need this ugliness in U-Boot. Let's take advantage of this and do something
clean and elegant in the device tree.
--
Timur Tabi
Linux kernel developer at Freescale
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