linux-kernel - Re: [PATCH v4 1/4] can: dev: Add support for limiting configured bitrate

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Message-ID: <4a96c6a8-b8c5-24a1-5e99-44751a0ae987@pengutronix.de>
Date:   Thu, 10 Aug 2017 17:29:13 +0200
From:   Marc Kleine-Budde <mkl@...gutronix.de>
To:     Franklin S Cooper Jr <fcooper@...com>,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        netdev@...r.kernel.org, linux-can@...r.kernel.org,
        wg@...ndegger.com, robh+dt@...nel.org,
        quentin.schulz@...e-electrons.com, dev.kurt@...dijck-laurijssen.be,
        andrew@...n.ch, sergei.shtylyov@...entembedded.com,
        socketcan@...tkopp.net
Subject: Re: [PATCH v4 1/4] can: dev: Add support for limiting configured
 bitrate

Hello,

sorry for stepping in late....

On 08/10/2017 02:59 AM, Franklin S Cooper Jr wrote:
> Various CAN or CAN-FD IP may be able to run at a faster rate than
> what the transceiver the CAN node is connected to. This can lead to
> unexpected errors. However, CAN transceivers typically have fixed
> limitations and provide no means to discover these limitations at
> runtime. Therefore, add support for a can-transceiver node that
> can be reused by other CAN peripheral drivers to determine for both
> CAN and CAN-FD what the max bitrate that can be used. If the user
> tries to configure CAN to pass these maximum bitrates it will throw
> an error.
> 
> Signed-off-by: Franklin S Cooper Jr <fcooper@...com>
> ---
> Version 4 changes:
> Used can-transceiver instead of fixed-transceiver.
> 
>  drivers/net/can/dev.c   | 50 +++++++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/can/dev.h |  5 +++++
>  2 files changed, 55 insertions(+)
> 
> diff --git a/drivers/net/can/dev.c b/drivers/net/can/dev.c
> index 365a8cc..372108f 100644
> --- a/drivers/net/can/dev.c
> +++ b/drivers/net/can/dev.c
> @@ -27,6 +27,7 @@
>  #include <linux/can/skb.h>
>  #include <linux/can/netlink.h>
>  #include <linux/can/led.h>
> +#include <linux/of.h>
>  #include <net/rtnetlink.h>
>  
>  #define MOD_DESC "CAN device driver interface"
> @@ -814,6 +815,39 @@ int open_candev(struct net_device *dev)
>  }
>  EXPORT_SYMBOL_GPL(open_candev);
>  
> +#ifdef CONFIG_OF
> +/*
> + * Common function that can be used to understand the limitation of
> + * a transceiver when it provides no means to determine these limitations
> + * at runtime.
> + */
> +void of_can_transceiver(struct net_device *dev)
> +{
> +	struct device_node *dn;
> +	struct can_priv *priv = netdev_priv(dev);
> +	struct device_node *np;
> +	unsigned int max_bitrate;
> +	int ret;
> +
> +	np = dev->dev.parent->of_node;
> +
> +	dn = of_get_child_by_name(np, "can-transceiver");
> +	if (!dn)
> +		return;
> +
> +	max_bitrate = 0;
> +	ret = of_property_read_u32(dn, "max-bitrate", &max_bitrate);

IIRC the last argument is only modified in case of no error, so what about:
	ret = of_property_read_u32(dn, "max-bitrate",
			&priv->max_bitrate);

> +
> +	if (max_bitrate > 0) {
> +		priv->max_bitrate = max_bitrate;
> +		priv->is_bitrate_limited = true;

Do we need is_bitrate_limited...

> +	} else if (ret != -EINVAL) {
> +		netdev_warn(dev, "Invalid value for transceiver max bitrate\n");
> +	}
> +}
> +EXPORT_SYMBOL(of_can_transceiver);
> +#endif
> +
>  /*
>   * Common close function for cleanup before the device gets closed.
>   *
> @@ -913,6 +947,14 @@ static int can_changelink(struct net_device *dev, struct nlattr *tb[],
>  					priv->bitrate_const_cnt);
>  		if (err)
>  			return err;
> +
> +		if (priv->is_bitrate_limited &&
> +		    bt.bitrate > priv->max_bitrate) {

...can we just use priv->max_bitrate?

	if (priv->max_bitrate && bt.bitrate > priv->max_bitrate)

> +			netdev_err(dev, "arbitration bitrate surpasses transceiver capabilities of %d bps\n",
> +				   priv->max_bitrate);
> +			return -EINVAL;
> +		}
> +
>  		memcpy(&priv->bittiming, &bt, sizeof(bt));
>  
>  		if (priv->do_set_bittiming) {
> @@ -997,6 +1039,14 @@ static int can_changelink(struct net_device *dev, struct nlattr *tb[],
>  					priv->data_bitrate_const_cnt);
>  		if (err)
>  			return err;
> +
> +		if (priv->is_bitrate_limited &&
> +		    dbt.bitrate > priv->max_bitrate) {
> +			netdev_err(dev, "canfd data bitrate surpasses transceiver capabilities of %d bps\n",
> +				   priv->max_bitrate);
> +			return -EINVAL;
> +		}
> +
>  		memcpy(&priv->data_bittiming, &dbt, sizeof(dbt));
>  
>  		if (priv->do_set_data_bittiming) {
> diff --git a/include/linux/can/dev.h b/include/linux/can/dev.h
> index 141b05a..5519f59 100644
> --- a/include/linux/can/dev.h
> +++ b/include/linux/can/dev.h
> @@ -47,6 +47,9 @@ struct can_priv {
>  	unsigned int data_bitrate_const_cnt;
>  	struct can_clock clock;
>  
> +	unsigned int max_bitrate;
> +	bool is_bitrate_limited;
> +
>  	enum can_state state;
>  
>  	/* CAN controller features - see include/uapi/linux/can/netlink.h */
> @@ -165,6 +168,8 @@ void can_put_echo_skb(struct sk_buff *skb, struct net_device *dev,
>  unsigned int can_get_echo_skb(struct net_device *dev, unsigned int idx);
>  void can_free_echo_skb(struct net_device *dev, unsigned int idx);
>  
> +void of_can_transceiver(struct net_device *dev);
> +
>  struct sk_buff *alloc_can_skb(struct net_device *dev, struct can_frame **cf);
>  struct sk_buff *alloc_canfd_skb(struct net_device *dev,
>  				struct canfd_frame **cfd);
> 

Marc

-- 
Pengutronix e.K.                  | Marc Kleine-Budde           |
Industrial Linux Solutions        | Phone: +49-231-2826-924     |
Vertretung West/Dortmund          | Fax:   +49-5121-206917-5555 |
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