[PATCH 1/3] Device tree binding documentation for gpio-switch

On 07/12/15 17:37, Rob Herring wrote:

+Linus W

On Fri, Dec 04, 2015 at 05:31:13PM +0000, Martyn Welch wrote:

quoted

This patch adds documentation for the gpio-switch binding. This binding
provides a mechanism to bind named links to gpio, with the primary
purpose of enabling standardised access to switches that might be standard
across a group of devices but implemented differently on each device.

This is good and what I suggested, but it now makes me wonder if switch
is generic enough. This boils down to needing to expose single gpio
lines to userspace with a defined function/use. IIRC, there's been some
discussion about this before along with improving the userspace
interface for GPIO in general. So I'd like to get Linus' thoughts on
this.

No problem. Rename gpio-signal?

quoted

Signed-off-by: Martyn Welch <martyn.welch@collabora.co.uk>
---
  .../devicetree/bindings/misc/gpio-switch.txt       | 47 ++++++++++++++++++++++
  1 file changed, 47 insertions(+)
  create mode 100644 Documentation/devicetree/bindings/misc/gpio-switch.txt

diff --git a/Documentation/devicetree/bindings/misc/gpio-switch.txt b/Documentation/devicetree/bindings/misc/gpio-switch.txt
new file mode 100644
index 0000000..13528bd
--- /dev/null
+++ b/Documentation/devicetree/bindings/misc/gpio-switch.txt

@@ -0,0 +1,47 @@
+Device-Tree bindings for gpio attached switches.
+
+This provides a mechanism to provide a named link to specified gpios. This can
+be useful in instances such as when theres a need to monitor a switch, which is
+common across a family of devices, but attached to different gpios and even
+implemented in different ways on differnet devices.
+
+Required properties:
+	- compatible = "gpio-switch";
+
+Each signal is represented as a sub-node of "gpio-switch". The naming of
+sub-nodes is arbitrary.
+
+Required sub-node properties:
+
+	- label: Name to be given to gpio switch.
+	- gpios: OF device-tree gpio specification.
+
+Optional sub-node properties:
+
+	- read-only: Boolean flag to mark the gpio as read-only, i.e. the line
+	  should not be driven by the host.

In terms a a switch use, allowing driving it would be an override of the
switch. Is that the idea here?

Yeah - since it had become a lot more generic and a lot of 
switches/signals would probably be implemented with a pull-up resistor 
of something like that, it seemed to make sense to allow them to be 
driven as well.

quoted

+
+Example nodes:
+
+        gpio-switch {
+                compatible = "gpio-switch";

Both from a binding and driver perspective, there is no point in
grouping these. Each node can simply have this compatible string.

True. I did it this way as this is how gpio-keys is implemented. OK, 
that has one optional parameter (autorepeat) for the block and this has 
none. Though I can also see that these probably have less in common than 
the individual lines used in gpio-keys.

quoted

+
+                write-protect {
+                        label = "write-protect";
+                        gpios = <&gpx3 0 GPIO_ACTIVE_LOW>;
+                        read-only;
+                };
+
+                developer-switch {
+                        label = "developer-switch";
+                        gpios = <&gpx1 3 GPIO_ACTIVE_HIGH>;
+                        read-only;
+                };
+
+                recovery-switch {
+                        label = "recovery-switch";
+                        gpios = <&gpx0 7 GPIO_ACTIVE_LOW>;
+                        read-only;
+                };
+        };
+
--
2.1.4