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

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

[Oleksij Rempel]

changes v3:
- use u32 instead of u16 for termination-ohms
- extend error handling

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                     | 66 +++++++++++++++++++
 include/linux/can/dev.h                       |  8 +++
 4 files changed, 100 insertions(+)

-- 
2.30.2

[PATCH v3 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..1f0e98051074 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.
+    minimum: 1
+    maximum: 65535
+
 additionalProperties: true
 
 ...
-- 
2.30.2

Re: [PATCH v3 1/3] dt-bindings: can-controller: add support for termination-gpios

[Rob Herring]

On Wed, 18 Aug 2021 09:12:30 +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(+)
> 

Reviewed-by: Rob Herring <robh@kernel.org>

[PATCH v3 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..3f0ee17c1461 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 = <120>;
+    };
-- 
2.30.2

Re: [PATCH v3 2/3] dt-bindings: can: fsl,flexcan: enable termination-* bindings

[Rob Herring]

On Wed, 18 Aug 2021 09:12:31 +0200, Oleksij Rempel wrote:
> 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(+)
> 

Reviewed-by: Rob Herring <robh@kernel.org>

[PATCH v3 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 | 66 +++++++++++++++++++++++++++++++++++++++
 include/linux/can/dev.h   |  8 +++++
 2 files changed, 74 insertions(+)

diff --git a/drivers/net/can/dev/dev.c b/drivers/net/can/dev/dev.c
index 311d8564d611..e3d840b81357 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 +401,69 @@ 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;
+	u32 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");
+
+	if (!gpio)
+		return 0;
+
+	ret = device_property_read_u32(dev, "termination-ohms", &term);
+	if (ret) {
+		netdev_err(ndev, "Cannot get termination-ohms: %pe\n",
+			   ERR_PTR(ret));
+		return ret;
+	}
+
+	if (term > U16_MAX) {
+		netdev_err(ndev, "Invalid termination-ohms value (%u > %u)\n",
+			   term, U16_MAX);
+		return -EINVAL;
+	}
+
+	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 +479,12 @@ 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

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

[Marc Kleine-Budde]

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On 18.08.2021 09:12:29, Oleksij Rempel wrote:
> changes v3:
> - use u32 instead of u16 for termination-ohms
> - extend error handling
> 
> 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

Applied to linux-can-next/testing

Thanks,
Marc
-- 
Pengutronix e.K.                 | Marc Kleine-Budde           |
Embedded Linux                   | https://www.pengutronix.de  |
Vertretung West/Dortmund         | Phone: +49-231-2826-924     |
Amtsgericht Hildesheim, HRA 2686 | Fax:   +49-5121-206917-5555 |

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