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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