Re: [PATCH 2/4] can: fix IFF_ECHO example in documentation

[Oliver Hartkopp]

On 04.08.26 21:55, Vincent Mailhol wrote:
> The documentation suggests doing:
>
>    dev->flags = (IFF_NOARP | IFF_ECHO);
>
> to set the IFF_ECHO flag. This is problematic because by doing so,
> other potentially enabled flags would be overwritten. Furthermore,
> none of the drivers do it like that.
>
> Replace the example by:
>
>    dev->flags |= IFF_ECHO;

IFF_NOARP is important for CAN interfaces and it looks like it could be 
missed now.

Please document that IFF_NOARP is already set in can_setup().
E.g. out of tree drivers might stumble into problems when they set up 
the flags differently.

> which is more robust and consistent with what all the drivers are doing.
>
> Signed-off-by: Vincent Mailhol <mailhol@xxxxxxxxxx>
> ---
>   Documentation/networking/can.rst | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/Documentation/networking/can.rst b/Documentation/networking/can.rst
> index 536ff411da1d..fbd0d501ea4e 100644
> --- a/Documentation/networking/can.rst
> +++ b/Documentation/networking/can.rst
> @@ -1126,7 +1126,7 @@ e.g. of tty devices. In this case the driver flag IFF_ECHO has to be
>   set to prevent the PF_CAN core from locally echoing sent frames
>   (aka loopback) as fallback solution::
>   
> -    dev->flags = (IFF_NOARP | IFF_ECHO);
> +    dev->flags |= IFF_ECHO;

Here also a documentation about IFF_NOARP is needed now.

Best regards,
Oliver