--- Tony Lindgren <[email protected]> wrote:
> Hi,
>
> * Jean Delvare <[email protected]> [060805 11:31]:
> >
> > > >> + if (armxor_rate > 16000000)
> > > >> + psc = (armxor_rate + 8000000) / 12000000;
> > > >> + else
> > > >> + psc = 0;
> > >
> > > >Can you please explain this formula?
> > >
> > > The OMAP core uses 8-bit value to divide the system clock (SCLK)
> and
> > > generates its own sampling clock (ICLK), and the core logic is
> sampled
> > > at clock rate of the system clock for the module, divided by
> (prescaler value + 1)
> >
> > I should have been more precise, I guess. What surprises me are the
> > numbers themselves. It's frequent to see forumlae of the form
> > "a = (b + c/2) / c" to divide with proper rounding, but here you
> have
> > 2c/3 instread of c/2. My question was more like: is it intentional,
> or a
> > typo? Also, with the code above, psc will never have value 1. The
> "if"
> > part will always compute to at least 2, and the "else" part to 0.
> Is
> > this OK?
> >
>
> Hmmm, this sounds like a bug somewhere. TRM for 5912 says the I2C
> clock
> must be prescaled to be between 7 - 12 MHz [1]. The XOR input clock
> is
> typically 12, 13 or 19.2 MHz. So we should have code that produces:
>
> XOR Mhz Divider Prescaler
> 12 1 0
> 13 2 1
> 19.2 2 1
>
> Then again the original old code produces something different too
> [2]...
>
> I suspect the original code had some hw workarounds and and later
> code
> may have a conversion bug somewhere :)
>
> I suggest we keep the code as is for now since it's known to work on
> all omaps, and then submit a follow-up patch later once we have
> verified that that code based on the TRM works on all omaps.
I have updated the driver with all other review comments except comment
on formula above by Jean. I can some part of description from Tony's
explanation along with removing the following code line
/* Set Own Address */
omap_i2c_write_reg(dev, OMAP_I2C_OA_REG, dev->own_address);
As it is not needed. Please confirm so that I can send the revised
patch soon.
---Komal Shah
http://komalshah.blogspot.com/
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