[PATCH] i2c: rk3x: adjust the LOW divison based on characteristics of SCL

Addy,

On Thu, Sep 25, 2014 at 6:40 PM, addy ke [off-list ref] wrote:

Hi, Doug

On 2014/9/26 5:52, Doug Anderson wrote:

quoted

Addy,

On Wed, Sep 24, 2014 at 9:36 PM, Doug Anderson [off-list ref] wrote:

quoted

Addy,

On Wed, Sep 24, 2014 at 6:56 PM, addy ke [off-list ref] wrote:

quoted

In my measurement,all paramter but "Data hold time" are match the characteristics of SCL bus line.
the measured value is 0.928us("data hold time on RK3X"  ~=  "the low period / 2")
but the maximum value described in table is 0.9us

About "Data hold time", there are described in I2C specification:
- for CBUS compatible masters for I2C-bus deivices
- the maximum data hold time has only be met if the device does not stretch the LOW period of the SCL signal.

I have tested on RK3288-Pinky board, there are no error.
But I don't known whether this paramter will affect i2c communications.

I'll have to spend more time tomorrow to really understand this, but
if changing the code to bias towards slightly longer "high" times
instead of "low" times helps fix it then that's fine with me.

So what you're saying is that you're seeing a case where the clock
goes low and the data is not valid until .928us.  Is this data that is
being driven by the master or data that is being driven by the slave?

It is driven by the master and will be release at half of LOW period in our IC design.

Ah, I didn't know this.  Is that in the TRM somewhere?

...so does it work to just replace:

    ideal_low_div = DIV_ROUND_UP(clk_rate * min_low_ns,
                                 scl_rate * 8 * min_total_ns)

...with:

    ideal_low_div = min_low_div


That will assign all "extra" time to the "high" part.

-Doug