Subject: Re: I2C bus clock on MPC85XX systems

From: Wolfgang Grandegger <[email-masked]>
Date: Tue, 22 Dec 2009 17:18:45 +0100

Felix Radensky wrote:
> Hi,
> 
> Almost all MPC85XX based systems have the compatible=:"fsl-i2c" in
> respective
> i2c device tree nodes. This causes FSL i2c driver to use the following
> "backward
> compatible" values: FSR=0x31 DFSR=0x10. This is regardless of CCB clock
> frequency and i2c clock prescaler.
> 
> On my custom MPC8536 based board with 432MHz CCB clock this results in
> 65KHz i2c clock frequency (checked with scope). U-Boot correctly configures
> the clock to 400KHz.
> 
> I've fixed the problem by modifying device tree to use different
> compatible value,
> similar to what socrates board does. Is this the right approach ?

Are you aware of the properties described in
"Documentation/powerpc/dts-bindings/fsl/i2c.txt":

http://lxr.linux.no/#linux+v2.6.32/Documentation/powerpc/dts-bindings/fsl/i2c.txt

Wolfgang.