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SubjectRe: meter ABI: (was Re: [PATCH v2 1/3] staging:iio:meter: Replaces IIO_DEV_ATTR_CH_OFF by IIO_DEVICE_ATTR)
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> On Mar 25, 2018, at 9:54 AM, Jonathan Cameron <jic23@kernel.org> wrote:
>
> On Sun, 25 Mar 2018 01:29:41 -0700
> John Syne <john3909@gmail.com> wrote:
>
>> Hi Jonathan,
> Hi John,
>
> Please wrap your normal emails (excepting tables) to 80 chars.
Yeah, I’m trying to do that, but I use a Mac and Apple Mail doesn’t
have a feature to wrap at 80 automatically so I have to do
this manually.
>
>>
>> I was speaking with Rodrigo and here is what I think must be done to move
>> ADE7878 out of staging
>>
>> Here are the steps as I see them:
>>
>> 1) Define the IIO Attributes so they are consistent with the IIO ABI. This
>> should be pretty simple given agreement on the naming convention.
> Please don't go just changing attribute names - the driver needs to
> use the standard approach of iio_chan_spec and create the vast
> majority of attributes automatically via that. There 'may' be
> a few corner cases wee don't want to make generic and they 'might'
> be exposed as attributes.
>
> I suspect this change is the 'big' job. The core support necessary
> for RMS and MAV (computedtype or whatever we call it) will need adding
> as well. That is a separate patch set with support for some examples
> in the dummy driver.
Great that you mentioned this, because I though we only needed to
modify the IIO_ATTR naming. I’ll take a look at iio_chan_spec and
the examples in the dummy driver.
>
>> 2) Map the ADE7854 interrupt status to IIO events. This requires an
>> interrupt processing section.
>> 3) Add DeviceTree support.
>> 4) Create DeviceTree overlay for the ADE7854.
> More a case of bindings for now. If those are used via an overlay
> fine but given we don't have any boards with one one in mainline,
> this is an implementation detail for the user rather than part
> of moving this driver out of staging.
I was thinking more along the lines of documentation to show a
developer what was needed to get the driver working.
>
>> 5) Update ADE7854 probe to read in the DeviceTree register settings.
>> 6) Add support for power modes (PM1, PM2).
> This isn't necessary for a move out of staging (nice to have though).
>
>> 7) Not sure if we will support measurement streaming on the ADE7854.
>> The problem is ADE7854 is designed as an SPI master, which means
>> it controls the SPI clock, so the driver must support SPI slave
>> mode. However, the Linux Kernel does not currently support SPI
>> slave mode. We have three choices to make this work and they
>> are all a lot of work: 1) Add support for SPI Slave mode to the
>> kernel, 2) Use hardware to convert SPI signals to I2S signals
>> and with the use of a custom codec, use the ALSA framework to
>> stream the samples (this is an approach I used, but I don’t like
>> it), 3) Move the I2S driver out of the sound subsystem and use it
>> together with DMA to stream samples directly into the ADE7854 driver
>> (my preferred solutions). Perhaps Mark Brown has some ideas on how
>> to make this work.
> I'll be honest, this is an end of line part and frankly more than
> a little crazy. I would go with simply not supporting the measurement
> streaming at all for this part. If you really need it we can then
> move onto the how part, but from what you have said I'm guessing you
> don't care except in an abstract 'it would be nice' sort of a way?
Yeah, I’m moving to the ADE9000 so I’ll drop this.
>
>>
>> The ADE9000 will be much easier because it uses an SPI Slave interface.
>>
>> I hope I have captured everything, but let me know if I have missed anything.
>>
>
> That will do for now ;) I'm sure there will be details that need
> tidying up once we have the above done, but that's true for any new
> driver (and this will be nearly a new driver before things are done).
Thank you again for all the detailed feedback.
>
> Jonathan

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