Need a clarification regarding I2C bus frequency in FreeBSD

[Ian Lepore]

On Fri, 2018-08-17 at 11:48 +0530, Rajesh Kumar wrote:
> Hi,
> 
> I am trying to use the I2C designware controller driver available in
> FreeBSD (ig4_iic.c) in our boards.
> 
> Is there a clean way, I can set the I2C bus frequency from the controller
> driver itself, rather than using device hints, FDT, tunables etc.,
> Something like, if the driver is loaded for our boards (identified using
> the PCI or ACPI ID's), then the frequency of the I2C bus needs to be
> hardcoded from driver itself. This is to avoid additional configs from the
> config file.
> 
> I tried adding a new interface "iicbus_set_frequency" (in line with
> iicbus_get_frequency) and tried calling that from the ig4 driver after the
> "iicbus" child is added.  But, iicbus instance is created only after ig4
> driver is loaded. So, calling iicbus_set_frequency after child addition
> leads to system panic (as there is no iicbus softc at this point).
> 
> Let me know if you need any details.
> 
> Thanks,
> Rajesh.

I don't really understand what you're asking for. The ig4_iic
controller driver doesn't appear to support bus frequency settings at
all, it just loads hard-coded values into the clock high/low registers
and never changes them. If you want to locally modify the driver to run
at a different hard-coded speed for your application, just change lines
589-592 in ig4_iic.c and continue to ignore the speed set by the bus
driver when handling iicbus_reset.

-- Ian