linux-kernel - Re: [PATCH 3/7] can: m_can: m_can_handle_state_errors(): fix CAN state transition to Error Active

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Message-Id: <DC74JEKBB6HL.1LJ53UZJ0T0Q9@baylibre.com>
Date: Wed, 20 Aug 2025 10:49:35 +0200
From: "Markus Schneider-Pargmann" <msp@...libre.com>
To: "Marc Kleine-Budde" <mkl@...gutronix.de>, "Chandrasekar Ramakrishnan"
 <rcsekar@...sung.com>, "Vincent Mailhol" <mailhol.vincent@...adoo.fr>,
 "Patrik Flykt" <patrik.flykt@...ux.intel.com>, "Dong Aisheng"
 <b29396@...escale.com>, "Fengguang Wu" <fengguang.wu@...el.com>, "Varka
 Bhadram" <varkabhadram@...il.com>, "Wu Bo" <wubo.oduw@...il.com>, "Philipp
 Zabel" <p.zabel@...gutronix.de>
Cc: <linux-can@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
 <kernel@...gutronix.de>
Subject: Re: [PATCH 3/7] can: m_can: m_can_handle_state_errors(): fix CAN
 state transition to Error Active

Hi,

On Tue Aug 12, 2025 at 7:36 PM CEST, Marc Kleine-Budde wrote:
> The CAN Error State is determined by the receive and transmit error
> counters. The CAN error counters decrease when reception/transmission
> is successful, so that a status transition back to the Error Active
> status is possible. This transition is not handled by
> m_can_handle_state_errors().
>
> Add the missing detection of the Error Active state to
> m_can_handle_state_errors() and extend the handling of this state in
> m_can_handle_state_change().
>
> Fixes: e0d1f4816f2a ("can: m_can: add Bosch M_CAN controller support")
> Fixes: cd0d83eab2e0 ("can: m_can: m_can_handle_state_change(): fix state change")
> Signed-off-by: Marc Kleine-Budde <mkl@...gutronix.de>
> ---
>  drivers/net/can/m_can/m_can.c | 48 ++++++++++++++++++++++++++-----------------
>  1 file changed, 29 insertions(+), 19 deletions(-)
>
> diff --git a/drivers/net/can/m_can/m_can.c b/drivers/net/can/m_can/m_can.c
> index a51dc0bb8124..b485d2f3d971 100644
> --- a/drivers/net/can/m_can/m_can.c
> +++ b/drivers/net/can/m_can/m_can.c
> @@ -812,6 +812,10 @@ static int m_can_handle_state_change(struct net_device *dev,
>  	u32 timestamp = 0;
>  
>  	switch (new_state) {
> +	case CAN_STATE_ERROR_ACTIVE:
> +		/* error active state */

This comment and the one below don't really help IMHO.

> +		cdev->can.state = CAN_STATE_ERROR_ACTIVE;
> +		break;
>  	case CAN_STATE_ERROR_WARNING:
>  		/* error warning state */
>  		cdev->can.can_stats.error_warning++;
> @@ -841,6 +845,13 @@ static int m_can_handle_state_change(struct net_device *dev,
>  	__m_can_get_berr_counter(dev, &bec);
>  
>  	switch (new_state) {
> +	case CAN_STATE_ERROR_ACTIVE:
> +		/* error active state */
> +		cf->can_id |= CAN_ERR_CRTL | CAN_ERR_CNT;
> +		cf->data[1] = CAN_ERR_CRTL_ACTIVE;
> +		cf->data[6] = bec.txerr;
> +		cf->data[7] = bec.rxerr;
> +		break;
>  	case CAN_STATE_ERROR_WARNING:
>  		/* error warning state */
>  		cf->can_id |= CAN_ERR_CRTL | CAN_ERR_CNT;
> @@ -877,30 +888,29 @@ static int m_can_handle_state_change(struct net_device *dev,
>  	return 1;
>  }
>  
> +static enum can_state
> +m_can_can_state_get_by_psr(const u32 psr)
> +{
> +	if (psr & PSR_BO)
> +		return CAN_STATE_BUS_OFF;
> +	if (psr & PSR_EP)
> +		return CAN_STATE_ERROR_PASSIVE;
> +	if (psr & PSR_EW)
> +		return CAN_STATE_ERROR_WARNING;

Why should m_can_handle_state_errors() should be called if none of these
flags are set?

m_can_handle_state_errors() seems to only be called if IR_ERR_STATE
which is defined as:
  #define IR_ERR_STATE	(IR_BO | IR_EW | IR_EP)

This is the for the interrupt register but will the PSR register bits be
set without the interrupt register being set?

Best
Markus

> +
> +	return CAN_STATE_ERROR_ACTIVE;
> +}
> +
>  static int m_can_handle_state_errors(struct net_device *dev, u32 psr)
>  {
>  	struct m_can_classdev *cdev = netdev_priv(dev);
> -	int work_done = 0;
> +	enum can_state new_state;
>  
> -	if (psr & PSR_EW && cdev->can.state != CAN_STATE_ERROR_WARNING) {
> -		netdev_dbg(dev, "entered error warning state\n");
> -		work_done += m_can_handle_state_change(dev,
> -						       CAN_STATE_ERROR_WARNING);
> -	}
> +	new_state = m_can_can_state_get_by_psr(psr);
> +	if (new_state == cdev->can.state)
> +		return 0;
>  
> -	if (psr & PSR_EP && cdev->can.state != CAN_STATE_ERROR_PASSIVE) {
> -		netdev_dbg(dev, "entered error passive state\n");
> -		work_done += m_can_handle_state_change(dev,
> -						       CAN_STATE_ERROR_PASSIVE);
> -	}
> -
> -	if (psr & PSR_BO && cdev->can.state != CAN_STATE_BUS_OFF) {
> -		netdev_dbg(dev, "entered error bus off state\n");
> -		work_done += m_can_handle_state_change(dev,
> -						       CAN_STATE_BUS_OFF);
> -	}
> -
> -	return work_done;
> +	return m_can_handle_state_change(dev, new_state);
>  }
>  
>  static void m_can_handle_other_err(struct net_device *dev, u32 irqstatus)


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