[PATCH v8 2/3] I2C: mediatek: Add driver for MediaTek I2C controller
Uwe Kleine-König
u.kleine-koenig at pengutronix.de
Wed May 20 01:33:35 PDT 2015
Hello Eddie,
On Wed, May 20, 2015 at 03:59:35PM +0800, Eddie Huang wrote:
> On Wed, 2015-05-20 at 09:11 +0200, Uwe Kleine-König wrote:
> > On Wed, May 20, 2015 at 10:40:11AM +0800, Eddie Huang wrote:
> > > On Mon, 2015-05-18 at 20:43 +0200, Uwe Kleine-König wrote:
> > > > On Tue, May 19, 2015 at 12:40:08AM +0800, Eddie Huang wrote:
> > > > > +/* calculate i2c port speed */
> > > > It would be nice to summarize the clock frequency settings here.
> > > > Something like:
> > > >
> > > > /*
> > > > * The input clock is divided by the value specified in the
> > > > * device tree as clock-div. The actual bus speed is then
> > > > * derived from this frequency by the following formula:
> > > > * ....
> > > >
> > > > This would make it possible to verify your calculations below.
> > >
> > > The comment will be:
> > > /*
> > > * khz: I2C bus clock
> > > * hclk: The input clock is divided by the value specified in the
> > > * device tree as clock-div
> > and which one of the two clocks you're writing about is hclk now? I
> > assume the divided one.
> > > * div = (sample_cnt + 1) * (step_cnt + 1)
> > > * khz = (hclk / 2) / div
> > khz for the 2nd time.
> >
> > > *
> > > * The calculation is to get div value that let result of
> > > * ((hclk / 2) / div) most approach and less than khz
> > > */
> > I imagined something more hardware related. A list of register (or
> > register bit fields) that influence the frequency and a formula
>
> > i2c_freq = parent_clk / clock-div * (...)
> >
> > (It seems to be a bit more complicated here as there are two registers
> > involved that are set differently depending on the target frequency.)
>
> Yes, hardware is a little complicated. I rewrite the comment:
>
> /*
> * Calculate i2c port speed
> *
> * Hardware design:
> * i2c_bus_freq = parent_clk / (clock-div * 2 * (sample_cnt) *
> (step_cnt))
> * clock-div: fixed in hardware, but may be various in different SoCs
... fixed in hardware, but different on different SoCs.
> *
> * The calculation want to pick the highest bus frequency that is still
> * less than or equal to i2c->speed_hz. and the calculation try to get
> * sample_cnt and step_cnt to fill in hardware register.
"The calculation picks the highest bus frequency that is still less than
or equal to i2c->speed_hz." and I'd drop the last sentence.
With that in mind I'll reply once more to the original patch.
Best regards
Uwe
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