On 15/03/2025 16:49, Sebastian Reichel wrote:
Hello,
On Sat, Mar 15, 2025 at 02:18:40PM +0100, David Heidelberg wrote:
On 14/03/2025 21:57, Sakari Ailus wrote:
Thanks for converting this to YAML.
On Fri, Mar 14, 2025 at 08:58:27PM +0100, David Heidelberg via B4 Relay wrote:
From: David Heidelberg <david@xxxxxxx>
Convert the Analog Devices ad5820 to DT schema format.
Add the previously undocumented io-channel-cells property,
which can be omitted. If present, it must be set to 0,
as the device provides only one channel.
What's the purpose of this property? The driver doesn't use it nor I think
it provides any information on the hardware either. The above description
also appears to be saying it's redundant.
Hello Sakari,
from my understanding, you're right.
I would prefer to drop it, see [1].
Anyway from reading of documentation I understood it may be right to have
the property empty, but also may be omitted. I saw both approaches in the
code.
If you choose not liking this redudancy, I push [1] and drop the property
here.
David
[1] https://patchwork.kernel.org/project/linux-omap/patch/20250213203208.93316-1-david@xxxxxxx/
Like all DT properties starting with #, this is not about hardware,
but about parsing the device tree itself and used by core DT code:
$ git grep io-channels drivers/of/property.c
drivers/of/property.c:DEFINE_SIMPLE_PROP(io_channels, "io-channels", "#io-channel-cells")
Have a look at the following example DT:
iio_device1: iio-provider1 {
#io-channel-cells = <2>;
};
iio_device2: iio-provider2 {
#io-channel-cells = <1>;
};
iio_device3: iio-provider3 {
#io-channel-cells = <0>;
};
example-iio-user {
my-iio-reference = <&iio_device1 AREA0 CHANNEL2>, <&iio_device3>, <&iio_device2 CHAN0>;
};
While you can easily understand that without the io-channel-cells,
please have a look what it looks like after sending it through the
DT compiler. You will get something like this:
iio-provider1 {
#io-channel-cells = <2>;
phandle = <23>;
};
iio-provider2 {
#io-channel-cells = <1>;
phandle = <10>;
};
iio-provider3 {
#io-channel-cells = <0>;
phandle = <37>;
};
example-iio-user {
my-iio-reference = <23 42 13 37 10 0>;
};
But you can safely drop it, when there are no references to the IIO
device. So it's obviously not required in all cases.
I hope I could explain the purpose well enough :)
This looks like a very good explanation, it helped me a lot.
Any chance to sneak it into the docs somewhere?
David
Greetings,
-- Sebastian
--
David Heidelberg
