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Message-Id: <20230722095710.17496-2-krzysztof.kozlowski@linaro.org>
Date: Sat, 22 Jul 2023 11:57:10 +0200
From: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To: Peter Rosin <peda@...ntia.se>, Andi Shyti <andi.shyti@...nel.org>,
Rob Herring <robh+dt@...nel.org>,
Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
Conor Dooley <conor+dt@...nel.org>,
Doug Anderson <dianders@...omium.org>,
linux-i2c@...r.kernel.org, devicetree@...r.kernel.org,
linux-kernel@...r.kernel.org
Cc: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Subject: [PATCH 2/2] dt-bindings: i2c: arb-gpio-challange: convert to DT schema
Convert the bindings for GPIO-based I2C Arbitration Using a Challenge &
Response Mechanism to DT schema.
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Acked-by: Douglas Anderson <dianders@...omium.org>
---
The text of original bindings was written by Doug, so please kindly ack
if you agree to relicense it from GPL-2 to (GPL-2.0-only OR
BSD-2-Clause).
Changes in v2:
1. Drop i2c-controller $ref in top-level part, because only children are
I2C controllers.
2. Add Ack.
---
.../bindings/i2c/i2c-arb-gpio-challenge.txt | 82 -----------
.../bindings/i2c/i2c-arb-gpio-challenge.yaml | 135 ++++++++++++++++++
.../devicetree/bindings/i2c/i2c-arb.txt | 35 -----
3 files changed, 135 insertions(+), 117 deletions(-)
delete mode 100644 Documentation/devicetree/bindings/i2c/i2c-arb-gpio-challenge.txt
create mode 100644 Documentation/devicetree/bindings/i2c/i2c-arb-gpio-challenge.yaml
delete mode 100644 Documentation/devicetree/bindings/i2c/i2c-arb.txt
diff --git a/Documentation/devicetree/bindings/i2c/i2c-arb-gpio-challenge.txt b/Documentation/devicetree/bindings/i2c/i2c-arb-gpio-challenge.txt
deleted file mode 100644
index 548a73cde796..000000000000
--- a/Documentation/devicetree/bindings/i2c/i2c-arb-gpio-challenge.txt
+++ /dev/null
@@ -1,82 +0,0 @@
-GPIO-based I2C Arbitration Using a Challenge & Response Mechanism
-=================================================================
-This uses GPIO lines and a challenge & response mechanism to arbitrate who is
-the master of an I2C bus in a multimaster situation.
-
-In many cases using GPIOs to arbitrate is not needed and a design can use
-the standard I2C multi-master rules. Using GPIOs is generally useful in
-the case where there is a device on the bus that has errata and/or bugs
-that makes standard multimaster mode not feasible.
-
-Note that this scheme works well enough but has some downsides:
-* It is nonstandard (not using standard I2C multimaster)
-* Having two masters on a bus in general makes it relatively hard to debug
- problems (hard to tell if i2c issues were caused by one master, another, or
- some device on the bus).
-
-
-Algorithm:
-
-All masters on the bus have a 'bus claim' line which is an output that the
-others can see. These are all active low with pull-ups enabled. We'll
-describe these lines as:
-
-- OUR_CLAIM: output from us signaling to other hosts that we want the bus
-- THEIR_CLAIMS: output from others signaling that they want the bus
-
-The basic algorithm is to assert your line when you want the bus, then make
-sure that the other side doesn't want it also. A detailed explanation is best
-done with an example.
-
-Let's say we want to claim the bus. We:
-1. Assert OUR_CLAIM.
-2. Waits a little bit for the other sides to notice (slew time, say 10
- microseconds).
-3. Check THEIR_CLAIMS. If none are asserted then the we have the bus and we are
- done.
-4. Otherwise, wait for a few milliseconds and see if THEIR_CLAIMS are released.
-5. If not, back off, release the claim and wait for a few more milliseconds.
-6. Go back to 1 (until retry time has expired).
-
-
-Required properties:
-- compatible: i2c-arb-gpio-challenge
-- our-claim-gpio: The GPIO that we use to claim the bus.
-- their-claim-gpios: The GPIOs that the other sides use to claim the bus.
- Note that some implementations may only support a single other master.
-- I2C arbitration bus node. See i2c-arb.txt in this directory.
-
-Optional properties:
-- slew-delay-us: microseconds to wait for a GPIO to go high. Default is 10 us.
-- wait-retry-us: we'll attempt another claim after this many microseconds.
- Default is 3000 us.
-- wait-free-us: we'll give up after this many microseconds. Default is 50000 us.
-
-
-Example:
- i2c@...a0000 {
- compatible = "acme,some-i2c-device";
- #address-cells = <1>;
- #size-cells = <0>;
- };
-
- i2c-arbitrator {
- compatible = "i2c-arb-gpio-challenge";
-
- i2c-parent = <&{/i2c@...A0000}>;
-
- our-claim-gpio = <&gpf0 3 1>;
- their-claim-gpios = <&gpe0 4 1>;
- slew-delay-us = <10>;
- wait-retry-us = <3000>;
- wait-free-us = <50000>;
-
- i2c-arb {
- #address-cells = <1>;
- #size-cells = <0>;
-
- i2c@52 {
- // Normal I2C device
- };
- };
- };
diff --git a/Documentation/devicetree/bindings/i2c/i2c-arb-gpio-challenge.yaml b/Documentation/devicetree/bindings/i2c/i2c-arb-gpio-challenge.yaml
new file mode 100644
index 000000000000..5bf6ce14c2dc
--- /dev/null
+++ b/Documentation/devicetree/bindings/i2c/i2c-arb-gpio-challenge.yaml
@@ -0,0 +1,135 @@
+# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/i2c/i2c-arb-gpio-challenge.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: GPIO-based I2C Arbitration Using a Challenge & Response Mechanism
+
+maintainers:
+ - Doug Anderson <dianders@...omium.org>
+ - Peter Rosin <peda@...ntia.se>
+
+description: |
+ This uses GPIO lines and a challenge & response mechanism to arbitrate who is
+ the master of an I2C bus in a multimaster situation.
+
+ In many cases using GPIOs to arbitrate is not needed and a design can use the
+ standard I2C multi-master rules. Using GPIOs is generally useful in the case
+ where there is a device on the bus that has errata and/or bugs that makes
+ standard multimaster mode not feasible.
+
+ Note that this scheme works well enough but has some downsides:
+ * It is nonstandard (not using standard I2C multimaster)
+ * Having two masters on a bus in general makes it relatively hard to debug
+ problems (hard to tell if i2c issues were caused by one master, another,
+ or some device on the bus).
+
+ Algorithm:
+ All masters on the bus have a 'bus claim' line which is an output that the
+ others can see. These are all active low with pull-ups enabled. We'll
+ describe these lines as:
+ * OUR_CLAIM: output from us signaling to other hosts that we want the bus
+ * THEIR_CLAIMS: output from others signaling that they want the bus
+
+ The basic algorithm is to assert your line when you want the bus, then make
+ sure that the other side doesn't want it also. A detailed explanation is
+ best done with an example.
+
+ Let's say we want to claim the bus. We:
+ 1. Assert OUR_CLAIM.
+ 2. Waits a little bit for the other sides to notice (slew time, say 10
+ microseconds).
+ 3. Check THEIR_CLAIMS. If none are asserted then the we have the bus and we
+ are done.
+ 4. Otherwise, wait for a few milliseconds and see if THEIR_CLAIMS are released.
+ 5. If not, back off, release the claim and wait for a few more milliseconds.
+ 6. Go back to 1 (until retry time has expired).
+
+properties:
+ compatible:
+ const: i2c-arb-gpio-challenge
+
+ i2c-parent:
+ $ref: /schemas/types.yaml#/definitions/phandle
+ description:
+ The I2C bus that this multiplexer's master-side port is connected to.
+
+ our-claim-gpios:
+ maxItems: 1
+ description:
+ The GPIO that we use to claim the bus.
+
+ slew-delay-us:
+ default: 10
+ description:
+ Time to wait for a GPIO to go high.
+
+ their-claim-gpios:
+ minItems: 1
+ maxItems: 2
+ description:
+ The GPIOs that the other sides use to claim the bus. Note that some
+ implementations may only support a single other master.
+
+ wait-free-us:
+ default: 50000
+ description:
+ We'll give up after this many microseconds.
+
+ wait-retry-us:
+ default: 3000
+ description:
+ We'll attempt another claim after this many microseconds.
+
+ i2c-arb:
+ type: object
+ $ref: /schemas/i2c/i2c-controller.yaml
+ unevaluatedProperties: false
+ description:
+ I2C arbitration bus node.
+
+required:
+ - compatible
+ - i2c-arb
+ - our-claim-gpios
+ - their-claim-gpios
+
+additionalProperties: false
+
+examples:
+ - |
+ #include <dt-bindings/gpio/gpio.h>
+ #include <dt-bindings/interrupt-controller/irq.h>
+
+ i2c-arbitrator {
+ compatible = "i2c-arb-gpio-challenge";
+ i2c-parent = <&i2c_4>;
+
+ our-claim-gpios = <&gpf0 3 GPIO_ACTIVE_LOW>;
+ their-claim-gpios = <&gpe0 4 GPIO_ACTIVE_LOW>;
+ slew-delay-us = <10>;
+ wait-retry-us = <3000>;
+ wait-free-us = <50000>;
+
+ i2c-arb {
+ #address-cells = <1>;
+ #size-cells = <0>;
+
+ sbs-battery@b {
+ compatible = "sbs,sbs-battery";
+ reg = <0xb>;
+ sbs,poll-retry-count = <1>;
+ };
+
+ embedded-controller@1e {
+ compatible = "google,cros-ec-i2c";
+ reg = <0x1e>;
+ interrupts = <6 IRQ_TYPE_LEVEL_HIGH>;
+ interrupt-parent = <&gpx1>;
+ pinctrl-names = "default";
+ pinctrl-0 = <&ec_irq>;
+ wakeup-source;
+ };
+ };
+ };
diff --git a/Documentation/devicetree/bindings/i2c/i2c-arb.txt b/Documentation/devicetree/bindings/i2c/i2c-arb.txt
deleted file mode 100644
index 59abf9277bdc..000000000000
--- a/Documentation/devicetree/bindings/i2c/i2c-arb.txt
+++ /dev/null
@@ -1,35 +0,0 @@
-Common i2c arbitration bus properties.
-
-- i2c-arb child node
-
-Required properties for the i2c-arb child node:
-- #address-cells = <1>;
-- #size-cells = <0>;
-
-Optional properties for i2c-arb child node:
-- Child nodes conforming to i2c bus binding
-
-
-Example :
-
- /*
- An NXP pca9541 I2C bus master selector at address 0x74
- with a NXP pca8574 GPIO expander attached.
- */
-
- arb@74 {
- compatible = "nxp,pca9541";
- reg = <0x74>;
-
- i2c-arb {
- #address-cells = <1>;
- #size-cells = <0>;
-
- gpio@38 {
- compatible = "nxp,pca8574";
- reg = <0x38>;
- #gpio-cells = <2>;
- gpio-controller;
- };
- };
- };
--
2.34.1
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