linux-kernel - Re: [PATCH v2 2/2] can: netlink: add interface for CAN-FD Transmitter Delay Compensation (TDC)

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Date:   Wed, 16 Jun 2021 16:29:40 +0200
From:   Marc Kleine-Budde <mkl@...gutronix.de>
To:     Vincent MAILHOL <mailhol.vincent@...adoo.fr>
Cc:     linux-can <linux-can@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        Oliver Hartkopp <socketcan@...tkopp.net>
Subject: Re: [PATCH v2 2/2] can: netlink: add interface for CAN-FD
 Transmitter Delay Compensation (TDC)

On 16.06.2021 22:53:02, Vincent MAILHOL wrote:
> On Wed. 16 Jun 2021 at 18:46, Marc Kleine-Budde <mkl@...gutronix.de> wrote:
> > On 04.06.2021 00:15:50, Vincent Mailhol wrote:
> > [...]
> >
> > > +static size_t can_tdc_get_size(const struct net_device *dev)
> > > +{
> > > +     struct can_priv *priv = netdev_priv(dev);
> > > +     size_t size;
> > > +
> > > +     if (!priv->tdc_const)
> > > +             return 0;
> > > +
> > > +     size = nla_total_size(0);                       /* nest IFLA_CAN_TDC */
> > > +     size += nla_total_size(sizeof(u32));            /* IFLA_CAN_TDCV_MAX */
> > > +     size += nla_total_size(sizeof(u32));            /* IFLA_CAN_TDCO_MAX */
> > > +     size += nla_total_size(sizeof(u32));            /* IFLA_CAN_TDCF_MAX */
> > > +
> > > +     if (priv->tdc.tdco) {
> >
> > Naively I'd say, iff the device has tdc_const give the user space the
> > tdc parameters, regardless if some value is 0 or not.
> >
> > What do you think?
> 
> I thought about that.
> The first important remark is that if tdc.tdco is zero, then TDC
> is off (c.f. documentation of struct can_tdc::tdco).
> 
> Let me illustrate my vision through examples.

[...]

examples makes sense \o/

[...]

> Finally, I have one side comment. It seems to me that you did not
> understand that the intent of
> |     if (priv->tdc.tdco)
> was to actually check whether TDC was on or off. In other words, my
> code was unclear.
> 
> I am now thinking to introduce an helper macro:
> static bool can_tdc_is_enabled(const struct can_priv *priv)
> |{
> |    return !!priv->tdc.tdco;
> |}
> 
> The code would look more clear like that.
> -     if (priv->tdc.tdco) {
> +     if (can_tdc_is_enabled(priv) {

Sounds good, I'm squashing this patch:

| diff --git a/drivers/net/can/dev/netlink.c b/drivers/net/can/dev/netlink.c
| index 6134bbf69c10..d48be574eae7 100644
| --- a/drivers/net/can/dev/netlink.c
| +++ b/drivers/net/can/dev/netlink.c
| @@ -311,7 +311,7 @@ static size_t can_tdc_get_size(const struct net_device *dev)
|         size += nla_total_size(sizeof(u32));            /* IFLA_CAN_TDCO_MAX */
|         size += nla_total_size(sizeof(u32));            /* IFLA_CAN_TDCF_MAX */
|  
| -       if (priv->tdc.tdco) {
| +       if (can_tdc_is_enabled(priv)) {
|                 size += nla_total_size(sizeof(u32));    /* IFLA_CAN_TDCV */
|                 size += nla_total_size(sizeof(u32));    /* IFLA_CAN_TDCO */
|                 size += nla_total_size(sizeof(u32));    /* IFLA_CAN_TDCF */
| @@ -352,6 +352,7 @@ static size_t can_get_size(const struct net_device *dev)
|                                        priv->data_bitrate_const_cnt);
|         size += sizeof(priv->bitrate_max);                      /* IFLA_CAN_BITRATE_MAX */
|         size += can_tdc_get_size(dev);                          /* IFLA_CAN_TDC */
| +
|         return size;
|  }
|  
| @@ -374,7 +375,7 @@ static int can_tdc_fill_info(struct sk_buff *skb, const struct net_device *dev)
|             nla_put_u32(skb, IFLA_CAN_TDC_TDCF_MAX, tdc_const->tdcf_max))
|                 goto err_cancel;
|  
| -       if (priv->tdc.tdco)
| +       if (can_tdc_is_enabled(priv)) {
|                 if (nla_put_u32(skb, IFLA_CAN_TDC_TDCV, tdc->tdcv) ||
|                     nla_put_u32(skb, IFLA_CAN_TDC_TDCO, tdc->tdco) ||
|                     nla_put_u32(skb, IFLA_CAN_TDC_TDCF, tdc->tdcf))
| diff --git a/include/linux/can/bittiming.h b/include/linux/can/bittiming.h
| index 9de6e9053e34..b6d1db1e7258 100644
| --- a/include/linux/can/bittiming.h
| +++ b/include/linux/can/bittiming.h
| @@ -83,6 +83,11 @@ struct can_tdc_const {
|         u32 tdcf_max;
|  };
|  
| +static inline bool can_tdc_is_enabled(const struct can_priv *priv)
| +{
| +       return !!priv->tdc.tdco;
| +}
| +
|  #ifdef CONFIG_CAN_CALC_BITTIMING
|  int can_calc_bittiming(struct net_device *dev, struct can_bittiming *bt,
|                        const struct can_bittiming_const *btc);

regards,
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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