Re: [coreboot] i2c_writeb vs i2c_raw_write output

[Kyösti Mälkki]

On Sun, Oct 9, 2016 at 2:09 AM, Duncan Laurie  wrote:
> On Fri, Oct 7, 2016 at 5:51 PM, Julius Werner 
> wrote:
> > Also, I think all of these functions only work on non-x86 devices
> > right now so they're probably not really helpful to you (I'd be
> > surprised if they even compile and link for your board). The I2C API
> > is unfortunately one of those areas where x86 and non-x86 coreboot
> > still lead very separate side-by-side lives right now. For x86 you
> > probably need the i2c_dev_xxx() functions, which should in theory work
>
> Skylake and Apollolake do support the I2C API and associated convenience
> functions. (finally!)  The i2c driver used is common for intel chipsets
> since haswell(core) and baytrail(atom), it just needs a bit of glue layer
> to map bus number to a base address.
>
> I added the i2c_dev_* variants around the same time in order to support
> drivers where the bus+address comes from devicetree, but the functions that
> take a bus+address will work too.
> > similar but I have no experience with them. You might also need to use
> > the smbus_xxx() functions instead (SMBUS is some
> > kinda-the-same-but-not-quite thing related to I2C on x86 that I never
> > bothered to fully understand).
>
> I agree this is likely what is needed for the ASROCK IMB-A180 as it looks
> like there is an smbus driver in the southbridge.  Look for
> i2c_smbus_send_byte() in include/device/smbus.h which is implemented in
> southbridge/amd/agesa/hudson/smbus.c

-duncan
>

I have not used this particular Beagle i2c/spi reade. As part of the
protocol, i2c/smbus master expects there is a slave device that first
acknowledges it address, and then also each byte you send to it. Maybe this
Beagle has a switch for that, but I think it acts more as LA just snooping
on the bus.

So you may need to add an actual i2c device (micro or PCF8574) on the bus
for the master side to work at all.

Kyösti
> On Thu, Sep 29, 2016 at 3:10 PM, Haleigh Novak  wrote:
> > > Hello All,
> > >
> > > I am currently trying to send POST codes from Coreboot (downloaded
> > > approximately a month ago) to a Beagle I2C/SPI reader, specifically via
> >
> > i2c.
> > > I don't know the register needed for i2c_writeb() so I figured I would
> >
> > use
> > > i2c_raw_write(). In general since I have been unable to locate anything
> > > explaining the difference between the two functions I would really
> > > appriciate it if someone could explain it or direct me to where I can
> >
> > find
> > > documentation. I am hoping that the explaination/resource will either
> >
> > tell
> > > me where / or direct me to how I can figure out where the i2c_raw_write
> >
> > will
> > > write to (if it will just write directly to the Beagle or somewhere
> >
> > else)?
> > > Or would it be better to send it to a register with i2c_writeb()? I am
> > > running Coreboot on an ASROCK Mainboard, model IMB-A180.
> > >
> > > Thank you.
> > >
> > > HN