Re: Doubts in getting started with the Analog AD7928 driver

["Ardelean, Alexandru" <alexandru.Ardelean@analog.com>]

On Tue, 2019-09-17 at 21:47 -0300, Daniel Junho wrote:
> On Tue, Sep 17, 2019 at 3:24 AM Ardelean, Alexandru
> <alexandru.Ardelean@analog.com> wrote:
> > On Mon, 2019-09-16 at 20:50 -0300, Daniel Junho wrote:
> > > [External]
> > > 
> > > Hello everybody.
> > > 
> > > I am still learning about kernel developing. I would like to try to
> > > develop a device driver for the AD7928 [1], from Analog Device.
> > > 
> > > Can someone give some words to guide me?
> > > 
> > > I was thinking about forking the analog kernel repo [2] but I don't
> > > know to which branch should I commit to when doing a pull request. Or
> > > if this is the correct way for the devices from Analog.
> > > 
> > 
> > Hey,
> > 
> > Thanks for the interest in writing the driver for this.
> > 
> > In some cases, some new parts may have an existing driver available
> > already
> > that can be re-used partially or completely.
> > 
> > You're in luck.
> > There is driver seems to be partially implemented via
> > drivers/iio/adc/ad7923.c
> > 
> > I've done only a minor/quick check but the control register bits are
> > compatible for the AD7928 as well.
> > 
> > Typically, you can extend that driver and add the new parts and test
> > them.
> > 
> > So, my suggestion would be:
> > 1. Get an eval-board or a AD7928 part; depending on the case we could
> > help
> > with this
> > 2. Try to set it up with a Raspberry Pi with the eval board
> >    a. it looks to me that you need a 7V-9V power-supply
> >    b. you can hook the SPI to the test-points on the eval board
> > 3. Write a basic device-tree overlay ; you can adapt something from
> > other
> > examples.
> > Look here:
> > https://github.com/analogdevicesinc/linux/blob/rpi-4.19.y/arch/arm/boot/dts/overlays/Makefile
> > Usually  rpi-adXXX.dts  are ADI parts.
> > 4. Enable the driver for the kernel.
> > If using the ADI kernel, there's a guide here for RPi.
> > https://wiki.analog.com/resources/tools-software/linux-build/generic/raspberrypi
> > Check the branch that matches your Raspbian image (rpi-4.19.y is the
> > latest)
> > 5. Build the kernel
> > 6. Write it to the SD-card image
> > 7. Test
> > 8. Modify & repeat
> > 
> > Thanks
> > Alex
> > 
> > > [1] https://www.analog.com/en/products/ad7928.html
> > > [2] https://github.com/analogdevicesinc/linux
> > > 
> > > Daniel Junho
> 
> Hi Alex.
> 
> It seems that using AD7923 will be the best choice. They are very
> similar.
> 
> Thank you for your reply and suggestion.
> I don't have an EVB, but at work, we have a board with the AD7928

If you have the chip already connected, then it's even better.
You don't need to go through the trouble of interfacing it anymore.

> using a user driver. So I will try to use it for this development, at

And if you've already validated with a user-driver, it's again better, as
the connections have been validated.

> least for now.
> 
> I believe that will be fun =)

Should be.
If this whole thing is new to you, it's always easier to start with a
base/existing driver and extend than go through the process of writing it
from scratch.
It's mostly how I learn(ed) things: taking things apart, seeing what people
have done, and then using the best ideas in my future processes.

> 
> Daniel Junho