[PATCH] at91sam9g45: fix i2c bus speed

[Jean-Christophe PLAGNIOL-VILLARD]

On 10:31 Thu 23 Sep     , Russell King - ARM Linux wrote:
> On Thu, Sep 23, 2010 at 11:22:36AM +0200, Peter Korsgaard wrote:
> > >>>>> "Nicolas" == Nicolas Ferre <nicolas.ferre at atmel.com> writes:
> > 
> > Hi,
> > 
> >  Nicolas> By the way, I suspect that at91sam9g20 has the same issue
> >  Nicolas> (400MHz core also)...
> > 
> >  Nicolas> We may also have a look at at91sam9g10 which embeds a 266MHz
> >  Nicolas> core....
> > 
> > Yes, but I don't have access that hw, so it's hard to know exact udelay
> > values. udelay=5 for 9g20 and udelay=3 for 9g10 probably aren't far off,
> > but it would be nice if someone with hw could test.
> 
> udelay(5) should always give something approximating a 5us delay, as we
> calibrate this delay loop against the system timer.  What I could believe
> is probably going on here is that writing to the hardware is adding
> additional delays - but that's nothing to do with the CPU speed itself.
 yeah right

I guess as the amba bus and the other IP also is faster so the time spend to
change the state of the pio differ for a chip to an other

and we can not fix it easly so I do think it will be better to pass the speed
of the bus that we want from the board and then calcualte it depending on the
SOC

as we will only have this issue when using bitbanging but we can do the same
for hardware i2c

Best Regards,
J.