Early access I2C and/or clock for iMX6?

[Sascha Hauer]

On Mon, Jun 20, 2016 at 03:34:06PM -0400, Michael D. Burkey wrote:
> In a quest to support the new Variscite SOM's EEPROM based DDR
> configuration, I am continuing to try to get all the pieces together.
> 
> Now that I have the SOM actually booting from IRAM, I am actually
> trying to get the "real" DDR configuration values out of the EEPROM on
> the SOM.
> 
> Which brings me to the next hurdle -- getting early I2C access up and running.
> 
> Thanks to some pointers from Sascha, I have been working with the
> fsl_i2c.c code that had already been used for this task on the mpc85xx
> PPC platform, and while the I2C controller is essentially the same,
> the clock tree  setup, etc. for the iMX6 is quite different.

The fsl_i2c.c driver as currently in arch/ppc/ needs the input clock
frequency and some timer for a timeout loop. The timeout could be
dropped from the loop which is ok for a early bringup driver. For the
input clock frequency you can pass in the reset default value,
statically compiled into the binary; no need to calculate it during
runtime. I still think fsl_i2c.c is the way to go, but you could also
you whatever else "early" variant of the driver, I wouldn't start from a
driver implementing the Linux I2C API though.

Sascha

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