Re: [PATCH v2 07/20] can: netlink: refactor CAN_CTRLMODE_TDC_{AUTO,MANUAL} flag reset logic

[Vincent Mailhol <mailhol@kernel.org>]

On 10/09/2025 at 15:03, Vincent Mailhol wrote:
> CAN_CTRLMODE_TDC_AUTO and CAN_CTRLMODE_TDC_MANUAL are mutually
> exclusive. This means that whenever the user switches from auto to
> manual mode (or vice versa), the other flag which was set previously
> needs to be cleared.
> 
> Currently, this is handled with a masking operation. It can be done in
> a simpler manner by clearing any of the previous TDC flags before
> copying netlink attributes. The code becomes easier to understand and
> will make it easier to add the new upcoming CAN XL flags which will
> have a similar reset logic as the current TDC flags.
> 
> Signed-off-by: Vincent Mailhol <mailhol@kernel.org>
> ---
>  drivers/net/can/dev/netlink.c | 9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/net/can/dev/netlink.c b/drivers/net/can/dev/netlink.c
> index 274eaab10796b601d565c32f6315727a578970bb..72a82d4e9d6494771320ea035ed6f6098c0e8ce6 100644
> --- a/drivers/net/can/dev/netlink.c
> +++ b/drivers/net/can/dev/netlink.c
> @@ -254,6 +254,10 @@ static int can_changelink(struct net_device *dev, struct nlattr *tb[],
>  		if ((maskedflags & ctrlstatic) != ctrlstatic)
>  			return -EOPNOTSUPP;
>  
> +		/* If a top dependency flag is provided, reset all its dependencies */
> +		if (cm->mask & CAN_CTRLMODE_FD)
> +			priv->ctrlmode &= !CAN_CTRLMODE_FD_TDC_MASK;
                                          ^

This is a bug. The correct operation to unset the flag is:

		priv->ctrlmode &= ~CAN_CTRLMODE_FD_TDC_MASK;

(replace the ! operator by ~).

@Marc, do you think you can send your next PR to net soonish?

I would like to rebase this series and the "rework the CAN MTU logic" series on
top of the MTU fix:

https://lore.kernel.org/linux-can/20250918-can-fix-mtu-v1-0-0d1cada9393b@kernel.org/

But to do so, I first need to wait for the MTU fix to appear on net-next and
there is not so much time left before the end of the development windows.

If the schedule is too short, let me know and I will adjust accordingly by
dropping whatever patches are in conflict.


Yours sincerely,
Vincent Mailhol