[PATCH v2 0/3] can: provide GPIO based termination

[PATCH v2 0/3] can: provide GPIO based termination

[Oleksij Rempel]

changes v2:
- add CAN_TERMINATION_GPIO_MAX
- remove fsl,scu-index from yaml example. It is not used on imx6q

Oleksij Rempel (3):
  dt-bindings: can-controller: add support for termination-gpios
  dt-bindings: can: fsl,flexcan: enable termination-* bindings
  can: dev: provide optional GPIO based termination support

 .../bindings/net/can/can-controller.yaml      |  9 ++++
 .../bindings/net/can/fsl,flexcan.yaml         | 17 ++++++
 drivers/net/can/dev/dev.c                     | 54 +++++++++++++++++++
 include/linux/can/dev.h                       |  8 +++
 4 files changed, 88 insertions(+)

-- 
2.30.2

[PATCH v2 1/3] dt-bindings: can-controller: add support for termination-gpios

[Oleksij Rempel]

Some boards provide GPIO controllable termination resistor. Provide
binding to make use of it.

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
---
 .../devicetree/bindings/net/can/can-controller.yaml      | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/Documentation/devicetree/bindings/net/can/can-controller.yaml b/Documentation/devicetree/bindings/net/can/can-controller.yaml
index 9cf2ae097156..298ce69a8208 100644
--- a/Documentation/devicetree/bindings/net/can/can-controller.yaml
+++ b/Documentation/devicetree/bindings/net/can/can-controller.yaml
@@ -13,6 +13,15 @@ properties:
   $nodename:
     pattern: "^can(@.*)?$"
 
+  termination-gpios:
+    description: GPIO pin to enable CAN bus termination.
+
+  termination-ohms:
+    description: The resistance value of the CAN bus termination resistor.
+    $ref: /schemas/types.yaml#/definitions/uint16-array
+    minimum: 1
+    maximum: 65535
+
 additionalProperties: true
 
 ...
-- 
2.30.2

Re: [PATCH v2 1/3] dt-bindings: can-controller: add support for termination-gpios

[Rob Herring]

On Tue, Aug 17, 2021 at 06:13:04AM +0200, Oleksij Rempel wrote:
> Some boards provide GPIO controllable termination resistor. Provide
> binding to make use of it.
> 
> Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
> ---
>  .../devicetree/bindings/net/can/can-controller.yaml      | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/net/can/can-controller.yaml b/Documentation/devicetree/bindings/net/can/can-controller.yaml
> index 9cf2ae097156..298ce69a8208 100644
> --- a/Documentation/devicetree/bindings/net/can/can-controller.yaml
> +++ b/Documentation/devicetree/bindings/net/can/can-controller.yaml
> @@ -13,6 +13,15 @@ properties:
>    $nodename:
>      pattern: "^can(@.*)?$"
>  
> +  termination-gpios:
> +    description: GPIO pin to enable CAN bus termination.

maxItems: 1

> +
> +  termination-ohms:
> +    description: The resistance value of the CAN bus termination resistor.
> +    $ref: /schemas/types.yaml#/definitions/uint16-array

Standard unit properties already have a type and are uint32.

> +    minimum: 1
> +    maximum: 65535
> +
>  additionalProperties: true
>  
>  ...
> -- 
> 2.30.2
> 
> 

[PATCH v2 2/3] dt-bindings: can: fsl,flexcan: enable termination-* bindings

[Oleksij Rempel]

Enable termination-* binding and provide validation example for it.

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
---
 .../bindings/net/can/fsl,flexcan.yaml           | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/Documentation/devicetree/bindings/net/can/fsl,flexcan.yaml b/Documentation/devicetree/bindings/net/can/fsl,flexcan.yaml
index 55bff1586b6f..2ae5443b3ace 100644
--- a/Documentation/devicetree/bindings/net/can/fsl,flexcan.yaml
+++ b/Documentation/devicetree/bindings/net/can/fsl,flexcan.yaml
@@ -119,6 +119,9 @@ properties:
     minimum: 0
     maximum: 2
 
+  termination-gpios: true
+  termination-ohms: true
+
 required:
   - compatible
   - reg
@@ -148,3 +151,17 @@ examples:
         fsl,stop-mode = <&gpr 0x34 28>;
         fsl,scu-index = /bits/ 8 <1>;
     };
+  - |
+    #include <dt-bindings/interrupt-controller/irq.h>
+    #include <dt-bindings/gpio/gpio.h>
+
+    can@2090000 {
+        compatible = "fsl,imx6q-flexcan";
+        reg = <0x02090000 0x4000>;
+        interrupts = <0 110 IRQ_TYPE_LEVEL_HIGH>;
+        clocks = <&clks 1>, <&clks 2>;
+        clock-names = "ipg", "per";
+        fsl,stop-mode = <&gpr 0x34 28>;
+        termination-gpios = <&gpio1 0 GPIO_ACTIVE_LOW>;
+        termination-ohms = /bits/ 16 <150>;
+    };
-- 
2.30.2

[PATCH v2 3/3] can: dev: provide optional GPIO based termination support

[Oleksij Rempel]

For CAN buses to work, a termination resistor has to be present at both
ends of the bus. This resistor is usually 120 Ohms, other values may be
required for special bus topologies.

This patch adds support for a generic GPIO based CAN termination. The
resistor value has to be specified via device tree, and it can only be
attached to or detached from the bus. By default the termination is not
active.

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
---
 drivers/net/can/dev/dev.c | 54 +++++++++++++++++++++++++++++++++++++++
 include/linux/can/dev.h   |  8 ++++++
 2 files changed, 62 insertions(+)

diff --git a/drivers/net/can/dev/dev.c b/drivers/net/can/dev/dev.c
index 311d8564d611..b4a6c7a6fc18 100644
--- a/drivers/net/can/dev/dev.c
+++ b/drivers/net/can/dev/dev.c
@@ -15,6 +15,7 @@
 #include <linux/can/dev.h>
 #include <linux/can/skb.h>
 #include <linux/can/led.h>
+#include <linux/gpio/consumer.h>
 #include <linux/of.h>
 
 #define MOD_DESC "CAN device driver interface"
@@ -400,10 +401,57 @@ void close_candev(struct net_device *dev)
 }
 EXPORT_SYMBOL_GPL(close_candev);
 
+static int can_set_termination(struct net_device *ndev, u16 term)
+{
+	struct can_priv *priv = netdev_priv(ndev);
+	int set;
+
+	if (term == priv->termination_gpio_ohms[CAN_TERMINATION_GPIO_ENABLED])
+		set = 1;
+	else
+		set = 0;
+
+	gpiod_set_value(priv->termination_gpio, set);
+
+	return 0;
+}
+
+static int can_get_termination(struct net_device *ndev)
+{
+	struct can_priv *priv = netdev_priv(ndev);
+	struct device *dev = ndev->dev.parent;
+	struct gpio_desc *gpio;
+	u16 term;
+	int ret;
+
+	/* Disabling termination by default is the safe choice: Else if many
+	 * bus participants enable it, no communication is possible at all.
+	 */
+	gpio = devm_gpiod_get_optional(dev, "termination", GPIOD_OUT_LOW);
+	if (IS_ERR(gpio))
+		return dev_err_probe(dev, PTR_ERR(gpio),
+				     "Cannot get termination-gpios\n");
+
+	ret = device_property_read_u16(dev, "termination-ohms", &term);
+	if (ret)
+		return ret;
+
+	priv->termination_const_cnt = ARRAY_SIZE(priv->termination_gpio_ohms);
+	priv->termination_const = priv->termination_gpio_ohms;
+	priv->termination_gpio = gpio;
+	priv->termination_gpio_ohms[CAN_TERMINATION_GPIO_DISABLED] =
+		CAN_TERMINATION_DISABLED;
+	priv->termination_gpio_ohms[CAN_TERMINATION_GPIO_ENABLED] = term;
+	priv->do_set_termination = can_set_termination;
+
+	return 0;
+}
+
 /* Register the CAN network device */
 int register_candev(struct net_device *dev)
 {
 	struct can_priv *priv = netdev_priv(dev);
+	int err;
 
 	/* Ensure termination_const, termination_const_cnt and
 	 * do_set_termination consistency. All must be either set or
@@ -419,6 +467,12 @@ int register_candev(struct net_device *dev)
 	if (!priv->data_bitrate_const != !priv->data_bitrate_const_cnt)
 		return -EINVAL;
 
+	if (!priv->termination_const) {
+		err = can_get_termination(dev);
+		if (err)
+			return err;
+	}
+
 	dev->rtnl_link_ops = &can_link_ops;
 	netif_carrier_off(dev);
 
diff --git a/include/linux/can/dev.h b/include/linux/can/dev.h
index 27b275e463da..2413253e54c7 100644
--- a/include/linux/can/dev.h
+++ b/include/linux/can/dev.h
@@ -32,6 +32,12 @@ enum can_mode {
 	CAN_MODE_SLEEP
 };
 
+enum can_termination_gpio {
+	CAN_TERMINATION_GPIO_DISABLED = 0,
+	CAN_TERMINATION_GPIO_ENABLED,
+	CAN_TERMINATION_GPIO_MAX,
+};
+
 /*
  * CAN common private data
  */
@@ -55,6 +61,8 @@ struct can_priv {
 	unsigned int termination_const_cnt;
 	const u16 *termination_const;
 	u16 termination;
+	struct gpio_desc *termination_gpio;
+	u16 termination_gpio_ohms[CAN_TERMINATION_GPIO_MAX];
 
 	enum can_state state;
 
-- 
2.30.2