Re: [PATCH v2 3/3] dt-bindings: iio: chemical: pms7003: add device tree support

On Thu, Jan 31, 2019 at 09:40:04PM +0100, Tomasz Duszynski wrote:

On Wed, Jan 30, 2019 at 10:12:54AM +0100, Johan Hovold wrote:

quoted

On Mon, Jan 28, 2019 at 07:43:33PM +0100, Tomasz Duszynski wrote:

quoted

On Mon, Jan 28, 2019 at 08:58:19AM +0100, Johan Hovold wrote:

quoted

On Sun, Jan 27, 2019 at 07:19:16PM +0100, Tomasz Duszynski wrote:

quoted

Add device tree support for Plantower PMS7003 particulate matter sensor.

Signed-off-by: Tomasz Duszynski <tduszyns@gmail.com>
---
 .../iio/chemical/plantower,pms7003.txt        | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/iio/chemical/plantower,pms7003.txt

diff --git a/Documentation/devicetree/bindings/iio/chemical/plantower,pms7003.txt b/Documentation/devicetree/bindings/iio/chemical/plantower,pms7003.txt
new file mode 100644
index 000000000000..e4c7f2fb1e30
--- /dev/null
+++ b/Documentation/devicetree/bindings/iio/chemical/plantower,pms7003.txt

@@ -0,0 +1,19 @@
+* Plantower PMS7003 particulate matter sensor
+
+Required properties:
+- compatible: must be "plantower,pms7003"
+
+Optional properties:
+- vcc-supply: phandle to the regulator that provides power to the sensor

Shouldn't this one be a required property?

Driver does not use regulator framework hence to me this property fits
here better.

The device tree describes hardware, not any particular driver.

That said, there is a bit of an on-going debate on whether mandatory
supplies (from a hardware perspective) should always be represented in
device tree or not.

	https://lore.kernel.org/lkml/20181123133126.GF2089@sirena.org.uk/T/#u (local)
        https://lore.kernel.org/lkml/20180409102244.GB11532@sirena.org.uk/T/#u (local)
	https://lore.kernel.org/lkml/20180425171123.xhyoay3nu463btoq@rob-hp-laptop/T/#u (local)

Even after going through this threads I am still unconvinced that
vcc-supply should be a requirement. Making this a mandatory property
would automatically imply using *_regulator_get() in a driver code
(on condition one is adding regulator support). In case there
isn't any physically connected we end up with a dummy one and a warning.

How would the device work at all without a physical vcc supply?

Is it how this should work?

As Mark mentioned in the threads above, you could add a fixed,
always-on regulator for cases where the device is always powered.

Boards failing to describe this supply would still work on Linux, but
would end up with a dummy regulator and a warning.

quoted

quoted

quoted

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+- set-gpios: phandle to the GPIO connected to the SET line
+- reset-gpios: phandle to the GPIO connected to the RESET line
+
+Refer to serial/slave-device.txt for generic serial attached device bindings.
+
+Example:
+
+&uart0 {
+	pms7003 {

The node name should be generic and reflect the functionality rather
than model. Perhaps "pms" will do here.

Agree, ideally we should have a generic dt name for this kind of sensors
(something like air-pollution-sensor perhaps?). But unfortunately there isn't
anything available now so I guess compatible part name should be okay
(besides this is the type of naming commonly used in other iio bindings).

What's wrong with particulate matter sensor ("pms")?

Seems like a better fix than any particular model name to me at least.

Personally I would vote for a more descriptive node name, for example:
particulate-matter-sensor or air-pollution-sensor or other name
which clearly shows what device we are dealing with.

Spelling it out seems preferable, yes. You know the domain better than
I do; I only suggest you come up with a generic node name.

Johan