Re: [PATCH v2 1/2] devicetree: i2c-hid: Add Wacom digitizer + regulator support

Hi Benjamin and Rob,

On Thu, Dec 01, 2016 at 03:34:34PM +0100, Benjamin Tissoires wrote:

On Nov 30 2016 or thereabouts, Brian Norris wrote:

quoted

From: Caesar Wang <redacted>

Add a compatible string and regulator property for Wacom W9103
digitizer. Its VDD supply may need to be enabled before using it.

Signed-off-by: Caesar Wang <redacted>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Jiri Kosina <jikos@kernel.org>
Cc: linux-input@vger.kernel.org
Signed-off-by: Brian Norris <briannorris@chromium.org>
---
v1 was a few months back. I finally got around to rewriting it based on
DT binding feedback.

v2:
 * add compatible property for wacom
 * name the regulator property specifically (VDD)

 Documentation/devicetree/bindings/input/hid-over-i2c.txt | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/Documentation/devicetree/bindings/input/hid-over-i2c.txt b/Documentation/devicetree/bindings/input/hid-over-i2c.txt
index 488edcb264c4..eb98054e60c9 100644
--- a/Documentation/devicetree/bindings/input/hid-over-i2c.txt
+++ b/Documentation/devicetree/bindings/input/hid-over-i2c.txt

@@ -11,12 +11,16 @@ If this binding is used, the kernel module i2c-hid will handle the communication
 with the device and the generic hid core layer will handle the protocol.
 
 Required properties:
-- compatible: must be "hid-over-i2c"
+- compatible: must be "hid-over-i2c", or a device-specific string like:
+    * "wacom,w9013"

NACK on this one.

After re-reading the v1 submission I realized Rob asked for this change,
but I strongly disagree.

HID over I2C is a generic protocol, in the same way HID over USB is. We
can not start adding device specifics here, this is opening the can of
worms. If the device is a HID one, nothing else should matter. The rest
(description of the device, name, etc...) is all provided by the
protocol.

I should have spoken up when Rob made the suggestion, because I more or
less agree with Benjamin here. I don't really see why this needs to have
a specialized compatible string, as the property is still fairly
generic, and the entire device handling is via a generic protocol. The
fact that we manage its power via a regulator is not very
device-specific.

quoted

 - reg: i2c slave address
 - hid-descr-addr: HID descriptor address
 - interrupt-parent: the phandle for the interrupt controller
 - interrupts: interrupt line
 
+Optional properties:
+- vdd-supply: phandle of the regulator that provides the supply voltage.

Agree on this one however.

Thanks.

As Benjamin noticed on patch 2, I added a delay property; I realized I
had been hacking that delay in to the regulator framework as a "ramp
delay" property, when in fact it was actually a property of *this*
device -- the 100 ms wait is a suggested wait for the HID firmware to
boot, not for the regulator to stabilize.

So, what do you two think about the following two properties?

 - vdd-supply, as in the quoted patch
 - init-delay-ms: time required by the device after power-on before it
   is ready for communication

And I'd drop the extra compatible property.

Brian