linux-kernel - Re: [PATCH v2 1/2] can: m_can: set init flag earlier in probe

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Message-ID: <zqk3dsg6qdr7nvul34cv5qygtrcq3h2kpwojr7e4nsbgvo2i6a@xbmfcgtb3uad>
Date: Mon, 23 Sep 2024 10:12:01 +0200
From: Markus Schneider-Pargmann <msp@...libre.com>
To: Matthias Schiffer <matthias.schiffer@...tq-group.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>, 
	Martin Hundebøll <martin@...nix.com>, "Felipe Balbi (Intel)" <balbi@...nel.org>, 
	Raymond Tan <raymond.tan@...el.com>, Jarkko Nikula <jarkko.nikula@...ux.intel.com>, 
	linux-can@...r.kernel.org, netdev@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux@...tq-group.com
Subject: Re: [PATCH v2 1/2] can: m_can: set init flag earlier in probe

On Thu, Sep 19, 2024 at 01:27:27PM GMT, Matthias Schiffer wrote:
> While an m_can controller usually already has the init flag from a
> hardware reset, no such reset happens on the integrated m_can_pci of the
> Intel Elkhart Lake. If the CAN controller is found in an active state,
> m_can_dev_setup() would fail because m_can_niso_supported() calls
> m_can_cccr_update_bits(), which refuses to modify any other configuration
> bits when CCCR_INIT is not set.
> 
> To avoid this issue, set CCCR_INIT before attempting to modify any other
> configuration flags.
> 
> Fixes: cd5a46ce6fa6 ("can: m_can: don't enable transceiver when probing")
> Signed-off-by: Matthias Schiffer <matthias.schiffer@...tq-group.com>
> ---
> 
> v2: no changes
> 
>  drivers/net/can/m_can/m_can.c | 14 +++++++++-----
>  1 file changed, 9 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/net/can/m_can/m_can.c b/drivers/net/can/m_can/m_can.c
> index 012c3d22b01dd..47481afb9add3 100644
> --- a/drivers/net/can/m_can/m_can.c
> +++ b/drivers/net/can/m_can/m_can.c
> @@ -1681,6 +1681,14 @@ static int m_can_dev_setup(struct m_can_classdev *cdev)
>  		return -EINVAL;
>  	}
>  
> +	/* Forcing standby mode should be redundant, as the chip should be in
> +	 * standby after a reset. Write the INIT bit anyways, should the chip
> +	 * be configured by previous stage.
> +	 */

Could you please update the comment to reflect your findings?

Best
Markus

> +	err = m_can_cccr_update_bits(cdev, CCCR_INIT, CCCR_INIT);
> +	if (err)
> +		return err;
> +
>  	if (!cdev->is_peripheral)
>  		netif_napi_add(dev, &cdev->napi, m_can_poll);
>  
> @@ -1732,11 +1740,7 @@ static int m_can_dev_setup(struct m_can_classdev *cdev)
>  		return -EINVAL;
>  	}
>  
> -	/* Forcing standby mode should be redundant, as the chip should be in
> -	 * 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);
> +	return 0;
>  }
>  
>  static void m_can_stop(struct net_device *dev)
> -- 
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