RE: [EXTERNAL] Re: [PATCH v3 3/5] Documentation: DT bindings for HID over SPI.

[Dmitry Antipov <dmanti@xxxxxxxxxxxxx>]

Hello Rob,

I just submitted patch v4 that addresses most of your feedback.

On Thu, Jan 20, 2022 at 12:07 PM,Rob Herring wrote:
> From: Rob Herring <robh@xxxxxxxxxx>
> 
> On Fri, Jan 14, 2022 at 06:31:33PM -0800, Dmitry Antipov wrote:
> > From: Dmitry Antipov <dmanti@xxxxxxxxxxxxx>
> >
> > Added documentation describes the required properties for implementing
> > Device Tree for a device supporting HID over SPI and also provides an
> > example.
> 
> Bindings are in DT schema format now.
> 
> >
> > Signed-off-by: Dmitry Antipov <dmanti@xxxxxxxxxxxxx>
> > ---
> >  .../bindings/input/hid-over-spi.txt           | 43 +++++++++++++++++++
> >  1 file changed, 43 insertions(+)
> >  create mode 100755
> > Documentation/devicetree/bindings/input/hid-over-spi.txt
> >
> > diff --git a/Documentation/devicetree/bindings/input/hid-over-spi.txt
> > b/Documentation/devicetree/bindings/input/hid-over-spi.txt
> > new file mode 100755
> > index 000000000000..5eba95b5724e
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/input/hid-over-spi.txt
> > @@ -0,0 +1,43 @@
> > +* HID over SPI Device-Tree bindings
> > +
> > +HID over SPI provides support for Human Interface Devices over the
> > +SPI bus. HID Over SPI Protocol Specification 1.0 was written by
> > +Microsoft and is available at
> https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.m
> icrosoft.com%2Fen-
> us%2Fdownload%2Fdetails.aspx%3Fid%3D103325&amp;data=04%7C01%7Cd
> manti%40microsoft.com%7Cb0b84680fa2c45bc2f3a08d9dc5063f6%7C72f988
> bf86f141af91ab2d7cd011db47%7C1%7C0%7C637783060144589082%7CUnkn
> own%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1h
> aWwiLCJXVCI6Mn0%3D%7C3000&amp;sdata=bWGZDRYtVovy3XYlpDsZ8xR2AL
> be5YoP0iSZ8xORSyA%3D&amp;reserved=0.
> > +
> > +If this binding is used, the kernel module spi-hid will handle the
> > +communication
> 
> What's a kernel module? ;) Bindings are OS independent (or supposed to be), so
> kernel details do not belong here.
> 
> > +with the device and the generic hid core layer will handle the protocol.
> > +
> > +Required properties:
> > +- compatible: must be "hid-over-spi"
> 
> Bindings describe devices, not protocols. There is no such 'hid-over-spi' device.
> Please see the existing hid-over-i2c binding.
> It's fine to have this compatible, but only as a fallback compatible.

In the v4 patch the yaml file expects the device-specific compatible
string, but also 'hid-over-spi'.

> 
> > +- interrupts: interrupt line
> > +- vdd-supply: phandle of the regulator that provides the supply
> > +voltage
> 
> What happens when the device has 2 supplies? And there's some timing
> requirement between them?

I am not sure if there is a way to account for all possible scenarios.
Our device only has one power regulator and the binding is now
device-specific.

> 
> > +- reset_gpio-gpios: gpio wired to the device reset line
> 
> 'reset-gpios' is the standard name.
> 
> > +- post-power-on-delay-ms: time required by the device after enabling
> > +its regulators or powering it on, before it is ready for
> > +communication
> > +- minimal-reset-delay-ms: minimum amount of time that device needs to
> > +be in reset state for the reset to take effect
> 
> These properties are what happens when we try to do generic bindings.
> It's a never-ending addition of more properties to try to describe
> (poorly) the power sequencing requirements.

I have made these optional in the v4 patch.

> 
> > +- input-report-header-address: this property and the rest are
> > +described in HID Over SPI Protocol Spec 1.0
> > +- input-report-body-address
> > +- output-report-address
> > +- read-opcode
> > +- write-opcode
> > +- flags
> 
> A bit too generic. We generally want to avoid having a property name with 2
> different types/meaning. It's not something we check for yet, but I plan to at
> some point.

I've made "flags" more specific in the v4 patch.

> 
> > +
> > +Example:
> > +	spi-hid-dev0 {
> > +		compatible = "hid-over-spi";
> > +		reg = <0>;
> > +		interrupts-extended = <&tlmm 42 IRQ_TYPE_EDGE_FALLING>;
> > +		vdd-supply = <&pm8350c_l3>;
> > +		input-report-header-address = <0x1000>;
> > +		input-report-body-address = <0x1004>;
> > +		output-report-address = <0x2000>;
> > +		read-opcode = <0x0b>;
> > +		write-opcode = <0x02>;
> > +		flags = <0x00>;
> > +		reset_gpio-gpios = <&tlmm 25 GPIO_ACTIVE_LOW>;
> > +		post-power-on-delay-ms = <5>;
> > +		minimal-reset-delay-ms = <5>;
> > +
> > +	};
> > --
> > 2.25.1
> >
> >