linux-kernel - Re: [PATCH v3] can: m_can: don't enable transceiver when probing

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Date: Sat, 1 Jun 2024 14:10:53 +0100
From: Simon Horman <horms@...nel.org>
To: Martin Hundebøll <martin@...nix.com>
Cc: Chandrasekar Ramakrishnan <rcsekar@...sung.com>,
	Marc Kleine-Budde <mkl@...gutronix.de>,
	Vincent Mailhol <mailhol.vincent@...adoo.fr>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Markus Schneider-Pargmann <msp@...libre.com>,
	linux-can@...r.kernel.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] can: m_can: don't enable transceiver when probing

On Thu, May 30, 2024 at 12:57:58PM +0200, Martin Hundebøll wrote:
> The m_can driver sets and clears the CCCR.INIT bit during probe (both
> when testing the NON-ISO bit, and when configuring the chip). After
> clearing the CCCR.INIT bit, the transceiver enters normal mode, where it
> affects the CAN bus (i.e. it ACKs frames). This can cause troubles when
> the m_can node is only used for monitoring the bus, as one cannot setup
> listen-only mode before the device is probed.
> 
> Rework the probe flow, so that the CCCR.INIT bit is only cleared when
> upping the device. First, the tcan4x5x driver is changed to stay in
> standby mode during/after probe. This in turn requires changes when
> setting bits in the CCCR register, as its CSR and CSA bits are always
> high in standby mode.
> 
> Signed-off-by: Martin Hundebøll <martin@...nix.com>
> ---
>  drivers/net/can/m_can/m_can.c         | 169 ++++++++++++++++----------
>  drivers/net/can/m_can/tcan4x5x-core.c |  13 +-
>  2 files changed, 116 insertions(+), 66 deletions(-)
> 
> diff --git a/drivers/net/can/m_can/m_can.c b/drivers/net/can/m_can/m_can.c

...

> @@ -1694,21 +1732,26 @@ static int m_can_dev_setup(struct m_can_classdev *cdev)
>  		return -EINVAL;
>  	}
>  
> -	if (cdev->ops->init)
> -		cdev->ops->init(cdev);
> -
> -	return 0;
> +	/* Forcing standby mode should be redunant, as the chip should be in

Hi Martin,

A minor nit from my side as it looks like there will be another revision
anyway.

redunant -> redundant

> +	 * standby after a reset. Write the INIT bit anyways, should the chip
> +	 * be configured by previous stage.
> +	 */
> +	return m_can_cccr_update_bits(cdev, CCCR_INIT, CCCR_INIT);
>  }

...