[PATCH 2/3 V3] i2c: mxs: Rework the PIO mode operation

[Wolfram Sang]

On Mon, Sep 30, 2013 at 01:23:54AM +0200, Marek Vasut wrote:
> Analyze and rework the PIO mode operation. The PIO mode operation
> was unreliable on MX28, by analyzing the bus with LA, the checks
> for when data were available or were to be sent were wrong.
> 
> The PIO WRITE has to be completely reworked as it multiple problems.
> The MX23 datasheet helped here, see comments in the code for details.
> The problems boil down to:
> - RUN bit in CTRL0 must be set after DATA register was written
> - The PIO transfer must be 4 bytes long tops, otherwise use
>   clock stretching.
> Both of these fixes are implemented.
> 
> The PIO READ operation can only be done for up to four bytes as
> we are unable to read out the data from the DATA register fast
> enough.
> 
> This patch also tries to document the investigation within the
> code.
> 
> Signed-off-by: Marek Vasut <marex at denx.de>

Please fix the checkpatch errors and build warning.

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