netdev - Re: [PATCH v7 4/7] can: Add Nuvoton NCT6694 CANFD support

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Message-ID: <20250228-magic-seahorse-of-abracadabra-f2a402-mkl@pengutronix.de>
Date: Fri, 28 Feb 2025 11:34:25 +0100
From: Marc Kleine-Budde <mkl@...gutronix.de>
To: Ming Yu <a0282524688@...il.com>
Cc: tmyu0@...oton.com, lee@...nel.org, linus.walleij@...aro.org, 
	brgl@...ev.pl, andi.shyti@...nel.org, mailhol.vincent@...adoo.fr, 
	andrew+netdev@...n.ch, davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org, 
	pabeni@...hat.com, wim@...ux-watchdog.org, linux@...ck-us.net, jdelvare@...e.com, 
	alexandre.belloni@...tlin.com, linux-kernel@...r.kernel.org, linux-gpio@...r.kernel.org, 
	linux-i2c@...r.kernel.org, linux-can@...r.kernel.org, netdev@...r.kernel.org, 
	linux-watchdog@...r.kernel.org, linux-hwmon@...r.kernel.org, linux-rtc@...r.kernel.org, 
	linux-usb@...r.kernel.org
Subject: Re: [PATCH v7 4/7] can: Add Nuvoton NCT6694 CANFD support

On 12.02.2025 10:49:43, Ming Yu wrote:
> > > +static void nct6694_can_handle_state_errors(struct net_device *ndev, u8 status)
> > > +{
> > > +     struct nct6694_can_priv *priv = netdev_priv(ndev);
> >
> > It seems you don't have dedicated RX and TX states, so call
> > nct6694_can_get_berr_counter() and use can_state_get_by_berr_counter()
> > to get the states. Then basically do that what what
> > mcp251xfd_handle_cerrif() does, starting with "new_state = max(tx_state, rx_state);"
> >
> 
> Excuse me, do you mean that nct6694_can_handle_state_change() the flow
> should like v5?
> https://lore.kernel.org/linux-can/CAMZ6RqLHEoukxDfV33iDWXjM1baK922QnWSkOP01VzZ0S_9H8g@mail.gmail.com/

The handling of
CAMZ6RqLHEoukxDfV33iDWXjM1baK922QnWSkOP01VzZ0S_9H8g@...l.gmail.com in v5
was better, but there were some questions by Vincent...

So let's continue the discussion from v5 here:

> > +static void nct6694_can_handle_state_change(struct net_device *ndev,
> > +                                           u8 status)
> > +{
> > +       struct nct6694_can_priv *priv = netdev_priv(ndev);
> > +       enum can_state new_state = priv->can.state;
> > +       enum can_state rx_state, tx_state;
> > +       struct can_berr_counter bec;
> > +       struct can_frame *cf;
> > +       struct sk_buff *skb;
> > +
> > +       nct6694_can_get_berr_counter(ndev, &bec);
> > +       can_state_get_by_berr_counter(ndev, &bec, &tx_state, &rx_state);
> 
> Here, you set up tx_state and rx_state...
> 

remove the switch (status)...

> > +       switch (status) {
> > +       case NCT6694_CAN_EVT_STS_ERROR_ACTIVE:
> > +               new_state = CAN_STATE_ERROR_ACTIVE;
> > +               break;
> > +       case NCT6694_CAN_EVT_STS_ERROR_PASSIVE:
> > +               new_state = CAN_STATE_ERROR_PASSIVE;
> > +               break;
> > +       case NCT6694_CAN_EVT_STS_BUS_OFF:
> > +               new_state = CAN_STATE_BUS_OFF;
> > +               break;
> > +       case NCT6694_CAN_EVT_STS_WARNING:
> > +               new_state = CAN_STATE_ERROR_WARNING;
> > +               break;
> > +       default:
> > +               netdev_err(ndev, "Receive unknown CAN status event.\n");
> > +               return;
> > +       }

replace it by:

	new_state = max(tx_state, rx_state);

> > +
> > +       /* state hasn't changed */
> > +       if (new_state == priv->can.state)
> > +               return;
> > +
> > +       skb = alloc_can_err_skb(ndev, &cf);
> > +

remove this VVV
> > +       tx_state = bec.txerr >= bec.rxerr ? new_state : 0;
> > +       rx_state = bec.txerr <= bec.rxerr ? new_state : 0;
            ^^^

> 
> ... but you never used the values returned by
> can_state_get_by_berr_counter() and just overwrote the tx and rx
> state.
> 
> What is the logic here? Why do you need to manually adjust those two
> values? Isn't the logic in can_change_state() sufficient?
> 
> > +       can_change_state(ndev, cf, tx_state, rx_state);
> > +
> > +       if (new_state == CAN_STATE_BUS_OFF) {

if (priv->can.state == CAN_STATE_BUS_OFF) {

> 
> Same for the new_state. The function can_change_state() calculate the
> new state from tx_state and rx_state and save it under
> can_priv->state. But here, you do your own calculation.
> 
> Only keep one of the two. If your device already tells you the state,
> then fine! Just use the information from your device and do not use
> can_change_state(). Here, you are doing double work resulting in a
> weird mix.
>

what does your device do when it goes into bus off?

> > +               can_bus_off(ndev);
> > +       } else if (skb) {
> > +               cf->can_id |= CAN_ERR_CNT;
> > +               cf->data[6] = bec.txerr;
> > +               cf->data[7] = bec.rxerr;
> > +       }
> > +

if (skb)

> > +       nct6694_can_rx_offload(&priv->offload, skb);
> > +}

regards,
Marc

-- 
Pengutronix e.K.                 | Marc Kleine-Budde          |
Embedded Linux                   | https://www.pengutronix.de |
Vertretung Nürnberg              | Phone: +49-5121-206917-129 |
Amtsgericht Hildesheim, HRA 2686 | Fax:   +49-5121-206917-9   |

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