On Mon. 16 Aug 2021 at 20:48, Oleksij Rempel <o.rempel@xxxxxxxxxxxxxx> wrote:
> 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@xxxxxxxxxxxxxx>
> ---
> drivers/net/can/dev/dev.c | 54 +++++++++++++++++++++++++++++++++++++++
> include/linux/can/dev.h | 7 +++++
> 2 files changed, 61 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..82bdc5b09a3a 100644
> --- a/include/linux/can/dev.h
> +++ b/include/linux/can/dev.h
> @@ -32,6 +32,11 @@ enum can_mode {
> CAN_MODE_SLEEP
> };
>
> +enum can_termination_gpio {
> + CAN_TERMINATION_GPIO_DISABLED = 0,
> + CAN_TERMINATION_GPIO_ENABLED,
I would add a last entry to automatically calculate the length of
the termination_gpio_ohms array.
+ CAN_TERMINATION_GPIO_MAX
> +};
> +
> /*
> * CAN common private data
> */
> @@ -55,6 +60,8 @@ struct can_priv {
> unsigned int termination_const_cnt;
> const u16 *termination_const;
> u16 termination;
> + struct gpio_desc *termination_gpio;
> + u16 termination_gpio_ohms[2];
This way, you can replace the constant value 2:
+ u16 termination_gpio_ohms[CAN_TERMINATION_GPIO_MAX];
>
> enum can_state state;
Yours sincerely,
Vincent
