Re: Doubts in getting started with the Analog AD7928 driver

[Jonathan Cameron <jic23@jic23.retrosnub.co.uk>]

On 28 November 2019 15:13:56 GMT, Daniel Junho <djunho@gmail.com> wrote:
>Hello.
>
>After some effort to extend the AD7923 to include the AD7928, I got
>stuck because it won't work.
>
>After several days trying to figure out, I could use an oscilloscope
>to analyze and, it seems that the cs_change does not affect the
>driver.
>
>```
>  struct spi_transfer t[] = {
>           {
>                   .tx_buf = &st->tx_buf[0],
>                   .len = 2,
>                   .cs_change = 1,
>           }, {
>                   .rx_buf = &st->rx_buf[0],
>                   .len = 2,
>           },
>   };
>   ret = spi_sync_transfer(st->spi, t, ARRAY_SIZE(t));
>```
>
>The code above sends the first cmd and does not deselect the cs to get
>the answer.
>
>I am using kernel 4.4.107 from Toradex to deploy the driver. That is
>the version used on the project of the board.
>
>Does anyone have any idea what I am doing wrong? Should I update the
>kernel, or it should work as well in this version? Or any ideas of how
>to debug it?

Sounds like an spi master driver issue.  What spi controller are you using? 

>
>Daniel E. M. Junho
>
>
>On Wed, Sep 18, 2019 at 3:13 AM Ardelean, Alexandru
><alexandru.Ardelean@analog.com> wrote:
>>
>> 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

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