On 30-06-17 15:53, Jonathan Cameron wrote:
On Fri, 30 Jun 2017 10:44:42 +0200
Mike Looijmans <mike.looijmans@xxxxxxxx> wrote:
I'm writing an IIO driver for a custom IP, which is pretty simple:
- Map the registers to memory and register IRQ routine
- To start acquisition, write a value to the config register
- On interrupt, read data register, push it into queue
- To stop, write another value to config.
Would it be useful to provide this as a generic driver in Linux, so that you
can provide the config register and data register offsets and values in the
devicetree? That would make it work on a lot of similar project without
everyone coding the same thing.
Hi Mike,
I've brought in the devicetree bindings maintainers and list as well on this
discussion because in many ways it's more about the strategy on bindings
than the actual driver... Also Linus Walleij for any experience handing
the gpio-mmio driver which strikes me as fairly similar in aim.
To the driver question, yes absolutely this would be a good thing to have.
The majority of ADCs out there are irritatingly more complex than what
you have. Everyone seems to feel obliged to put in their own 'special
sauce'.
As for bindings, there are two options, either we
1) As you suggest push all differences between different parts into the
bindings. Note we'll still need a compatible list in the driver.
So this is something like gpio-mmio.c
2) Do something similar to the irq generic_chip (CONFIG_GENERIC_IRQ)
infrastructure and actually have very slim wrapper drivers around a
library. That allows those elements that are constrained by the
hardware to not need specifying in device tree bindings.
And a related question: Is there a driver that's close to this?
I can't immediately think of one, but it's possible that one
of the SoC ADC drivers is simple enough to describe this way.
So Mark / Rob. You guys have experience with how the bindings
worked out for each approach. Which do you prefer?
Either approach is fine with me.
Mike, perhaps you have an initial cut of some bindings that might
help the discussion to move along?
I was thinking along these lines:
... {
compatible = "iio-adc-generic-mmio";
reg = <0x43210000 4096>;
interrupt = <&gic 42 0>;
iio,start-sequence = <0x0 0x3> <0x4 0xff>;
iio,stop-sequence = <0x0 0x0>;
iio,data-register = <0x10>;
};
Required:
compatible: must be "iio-adc-generic-mmio";
reg: Memory address and range of IP platform device
interrupt: Data-ready interrupt binding
Optional:
iio,data-register: Offset where to read data. Defaults to <0>.
iio,start-sequence: Array of <offset value> pairs. On start of acquisition
the driver writes each value to each offset in order.
iio,stop-sequence: Array of <offset value> pairs to stop acquisition.
And we could make up more properties as we go, like the number of valid data
bits and shift, interrupt rate and fifo buffer properties...
We could add normal clock and power supply bindings as well, so it would
enable them on starting data acquisition.
For now the bad news is that the project was put on hold, so I'm not allowed
to spend serious development time now.
Kind regards,
Mike Looijmans
System Expert
TOPIC Products
Materiaalweg 4, NL-5681 RJ Best
Postbus 440, NL-5680 AK Best
Telefoon: +31 (0) 499 33 69 79
E-mail: mike.looijmans@xxxxxxxxxxxxxxxxx
Website: www.topicproducts.com
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