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Date:      Sun, 19 Aug 2018 19:23:22 +0530
From:      Rajesh Kumar <rajfbsd@gmail.com>
To:        ian@freebsd.org
Cc:        freebsd-drivers@freebsd.org, freebsd-hackers@freebsd.org
Subject:   Re: Need a clarification regarding I2C bus frequency in FreeBSD
Message-ID:  <CAAO%2BANOs_YVov-d21Em1EHzajQw7wHsxkzZCnsZwkfBr2=mEiA@mail.gmail.com>
In-Reply-To: <1534523216.27158.17.camel@freebsd.org>
References:  <CAAO%2BANOXwXAzJt%2BBZez6422jqKjrKPboSe_%2BudnOCWxYqE-=sQ@mail.gmail.com> <1534523216.27158.17.camel@freebsd.org>

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Hi Ian,

Basically, I want to set the I2C clock frequency for Designware IP in our
board to 150Mhz.  So, I was looking for the way in FreeBSD.

So, Is this the frequency which is configured through the clock high/low
registers? I see the those register are coded to 100 and 125 currently, I
am not sure how that value is arrived. If it needs to be configured for
150Mhz, how to derive the appropriate values? I looked at the DW_apb_i2c
databook section 3.11 to understand about it.  I am still unclear.  I see a
comment saying "Program based on 25000 Hz clock". In my case, should they
be programmed based on 150Mhz clock?


On Fri, Aug 17, 2018 at 9:57 PM Ian Lepore <ian@freebsd.org> wrote:

> 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
>



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