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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@linaro.org> Acked-by: Douglas Anderson <dianders@chromium.org> Link: https://lore.kernel.org/r/20230731163833.319258-2-krzysztof.kozlowski@linaro.org Signed-off-by: Andi Shyti <andi.shyti@kernel.org>
This commit is contained in:
Krzysztof Kozlowski
Andi Shyti
parent
4f68ead61b
commit
5578e75140
@ -1,82 +0,0 @@
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GPIO-based I2C Arbitration Using a Challenge & Response Mechanism
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=================================================================
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This uses GPIO lines and a challenge & response mechanism to arbitrate who is
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the master of an I2C bus in a multimaster situation.
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In many cases using GPIOs to arbitrate is not needed and a design can use
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the standard I2C multi-master rules. Using GPIOs is generally useful in
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the case where there is a device on the bus that has errata and/or bugs
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that makes standard multimaster mode not feasible.
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Note that this scheme works well enough but has some downsides:
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* It is nonstandard (not using standard I2C multimaster)
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* Having two masters on a bus in general makes it relatively hard to debug
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problems (hard to tell if i2c issues were caused by one master, another, or
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some device on the bus).
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Algorithm:
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All masters on the bus have a 'bus claim' line which is an output that the
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others can see. These are all active low with pull-ups enabled. We'll
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describe these lines as:
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- OUR_CLAIM: output from us signaling to other hosts that we want the bus
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- THEIR_CLAIMS: output from others signaling that they want the bus
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The basic algorithm is to assert your line when you want the bus, then make
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sure that the other side doesn't want it also. A detailed explanation is best
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done with an example.
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Let's say we want to claim the bus. We:
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1. Assert OUR_CLAIM.
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2. Waits a little bit for the other sides to notice (slew time, say 10
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microseconds).
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3. Check THEIR_CLAIMS. If none are asserted then the we have the bus and we are
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done.
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4. Otherwise, wait for a few milliseconds and see if THEIR_CLAIMS are released.
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5. If not, back off, release the claim and wait for a few more milliseconds.
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6. Go back to 1 (until retry time has expired).
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Required properties:
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- compatible: i2c-arb-gpio-challenge
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- our-claim-gpio: The GPIO that we use to claim the bus.
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- their-claim-gpios: The GPIOs that the other sides use to claim the bus.
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Note that some implementations may only support a single other master.
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- I2C arbitration bus node. See i2c-arb.txt in this directory.
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Optional properties:
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- slew-delay-us: microseconds to wait for a GPIO to go high. Default is 10 us.
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- wait-retry-us: we'll attempt another claim after this many microseconds.
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Default is 3000 us.
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- wait-free-us: we'll give up after this many microseconds. Default is 50000 us.
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Example:
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i2c@12ca0000 {
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compatible = "acme,some-i2c-device";
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#address-cells = <1>;
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#size-cells = <0>;
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};
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i2c-arbitrator {
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compatible = "i2c-arb-gpio-challenge";
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i2c-parent = <&{/i2c@12CA0000}>;
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our-claim-gpio = <&gpf0 3 1>;
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their-claim-gpios = <&gpe0 4 1>;
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slew-delay-us = <10>;
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wait-retry-us = <3000>;
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wait-free-us = <50000>;
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i2c-arb {
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#address-cells = <1>;
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#size-cells = <0>;
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i2c@52 {
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// Normal I2C device
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};
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};
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};
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@ -0,0 +1,135 @@
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# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
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%YAML 1.2
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---
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$id: http://devicetree.org/schemas/i2c/i2c-arb-gpio-challenge.yaml#
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$schema: http://devicetree.org/meta-schemas/core.yaml#
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title: GPIO-based I2C Arbitration Using a Challenge & Response Mechanism
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maintainers:
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- Doug Anderson <dianders@chromium.org>
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- Peter Rosin <peda@axentia.se>
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description: |
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This uses GPIO lines and a challenge & response mechanism to arbitrate who is
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the master of an I2C bus in a multimaster situation.
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In many cases using GPIOs to arbitrate is not needed and a design can use the
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standard I2C multi-master rules. Using GPIOs is generally useful in the case
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where there is a device on the bus that has errata and/or bugs that makes
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standard multimaster mode not feasible.
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Note that this scheme works well enough but has some downsides:
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* It is nonstandard (not using standard I2C multimaster)
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* Having two masters on a bus in general makes it relatively hard to debug
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problems (hard to tell if i2c issues were caused by one master, another,
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or some device on the bus).
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Algorithm:
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All masters on the bus have a 'bus claim' line which is an output that the
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others can see. These are all active low with pull-ups enabled. We'll
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describe these lines as:
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* OUR_CLAIM: output from us signaling to other hosts that we want the bus
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* THEIR_CLAIMS: output from others signaling that they want the bus
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The basic algorithm is to assert your line when you want the bus, then make
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sure that the other side doesn't want it also. A detailed explanation is
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best done with an example.
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Let's say we want to claim the bus. We:
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1. Assert OUR_CLAIM.
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2. Waits a little bit for the other sides to notice (slew time, say 10
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microseconds).
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3. Check THEIR_CLAIMS. If none are asserted then the we have the bus and we
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are done.
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4. Otherwise, wait for a few milliseconds and see if THEIR_CLAIMS are released.
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5. If not, back off, release the claim and wait for a few more milliseconds.
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6. Go back to 1 (until retry time has expired).
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properties:
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compatible:
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const: i2c-arb-gpio-challenge
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i2c-parent:
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$ref: /schemas/types.yaml#/definitions/phandle
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description:
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The I2C bus that this multiplexer's master-side port is connected to.
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our-claim-gpios:
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maxItems: 1
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description:
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The GPIO that we use to claim the bus.
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slew-delay-us:
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default: 10
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description:
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Time to wait for a GPIO to go high.
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their-claim-gpios:
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minItems: 1
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maxItems: 8
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description:
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The GPIOs that the other sides use to claim the bus. Note that some
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implementations may only support a single other master.
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wait-free-us:
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default: 50000
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description:
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We'll give up after this many microseconds.
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wait-retry-us:
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default: 3000
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description:
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We'll attempt another claim after this many microseconds.
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i2c-arb:
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type: object
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$ref: /schemas/i2c/i2c-controller.yaml
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unevaluatedProperties: false
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description:
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I2C arbitration bus node.
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required:
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- compatible
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- i2c-arb
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- our-claim-gpios
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- their-claim-gpios
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additionalProperties: false
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examples:
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- |
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#include <dt-bindings/gpio/gpio.h>
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#include <dt-bindings/interrupt-controller/irq.h>
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i2c-arbitrator {
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compatible = "i2c-arb-gpio-challenge";
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i2c-parent = <&i2c_4>;
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our-claim-gpios = <&gpf0 3 GPIO_ACTIVE_LOW>;
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their-claim-gpios = <&gpe0 4 GPIO_ACTIVE_LOW>;
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slew-delay-us = <10>;
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wait-retry-us = <3000>;
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wait-free-us = <50000>;
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i2c-arb {
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#address-cells = <1>;
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#size-cells = <0>;
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sbs-battery@b {
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compatible = "sbs,sbs-battery";
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reg = <0xb>;
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sbs,poll-retry-count = <1>;
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};
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embedded-controller@1e {
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compatible = "google,cros-ec-i2c";
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reg = <0x1e>;
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interrupts = <6 IRQ_TYPE_LEVEL_HIGH>;
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interrupt-parent = <&gpx1>;
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pinctrl-names = "default";
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pinctrl-0 = <&ec_irq>;
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wakeup-source;
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};
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};
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};
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@ -1,35 +0,0 @@
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Common i2c arbitration bus properties.
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- i2c-arb child node
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Required properties for the i2c-arb child node:
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- #address-cells = <1>;
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- #size-cells = <0>;
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Optional properties for i2c-arb child node:
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- Child nodes conforming to i2c bus binding
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Example :
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/*
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An NXP pca9541 I2C bus master selector at address 0x74
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with a NXP pca8574 GPIO expander attached.
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*/
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arb@74 {
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compatible = "nxp,pca9541";
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reg = <0x74>;
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i2c-arb {
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#address-cells = <1>;
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#size-cells = <0>;
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gpio@38 {
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compatible = "nxp,pca8574";
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reg = <0x38>;
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#gpio-cells = <2>;
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gpio-controller;
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};
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};
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};
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