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Date: Fri, 25 Jul 2008 11:04:54 +0200
From: Wolfgang Grandegger <wg@grandegger.com>
MIME-Version: 1.0
To: Jochen Friedrich <jochen@scram.de>
Subject: Re: [PATCH] powerpc: i2c-mpc: make speed registers configurable via
	FDT
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Cc: Scott Wood <scottwood@freescale.com>, Linuxppc-dev@ozlabs.org
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Jochen Friedrich wrote:
> Hi Wolfgang,
> 
>> The I2C driver for the MPC currently uses a fixed speed hard-coded into
>> the driver. This patch adds the FDT properties "fdr" and "dfsrr" for the
>> corresponding I2C registers to make the speed configurable via FDT, 
>> e.g.:
>>
>>     i2c@3100 {
>>         compatible = "fsl-i2c";
>>         reg = <0x3100 0x100>;
>>         interrupts = <43 2>;
>>         interrupt-parent = <&mpic>;
>>         dfsrr = <0x20>;
>>         fdr = <0x03>;
>>     };
> 
> 
> Would it be possible to use the standard property "clock-frequency" for this
> and calculate the register settings in the driver?

Almost everything is possible in software, just for what price ;-). 
U-Boot has some code in drivers/i2c/fsl_i2c.c to determine reasonable 
fdr and dfsrr values for the MPC83/5/6xx boards. For the MPC82xx and 
MPC85xx it's even more sophisticated.

I was also thinking to just overtake the U-Boot settings if fdt and 
dfsrr is not defined for the I2C node (instead of the debatable default 
values).

Wolfgang.