linux-kernel - Re: [PATCH] net: can: fix build dependency

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Message-ID: <cdcb2a82-e05f-4cdb-907b-15643f615a58@hartkopp.net>
Date: Thu, 4 Dec 2025 19:03:12 +0100
From: Oliver Hartkopp <socketcan@...tkopp.net>
To: Arnd Bergmann <arnd@...nel.org>, Marc Kleine-Budde <mkl@...gutronix.de>,
 Vincent Mailhol <mailhol@...nel.org>
Cc: Arnd Bergmann <arnd@...db.de>, Jimmy Assarsson <extja@...ser.com>,
 linux-can@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: can: fix build dependency

Hello Arnd,

On 04.12.25 11:00, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@...db.de>
> 
> A recent bugfix introduced a new problem with Kconfig dependencies:
> 
> WARNING: unmet direct dependencies detected for CAN_DEV
>    Depends on [n]: NETDEVICES [=n] && CAN [=m]
>    Selected by [m]:
>    - CAN [=m] && NET [=y]
> 
> Since the CAN core code now links into the CAN device code, that
> particular function needs to be available, though the rest of it
> does not.
> 
> Revert the incomplete fix and instead use Makefile logic to avoid
> the link failure.
> 
> Fixes: cb2dc6d2869a ("can: Kconfig: select CAN driver infrastructure by default")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

Tested-by: Oliver Hartkopp <socketcan@...tkopp.net>
Acked-by: Oliver Hartkopp <socketcan@...tkopp.net>

I'm still not sure what this patch really does but it works excellent 
and fits exactly what is intended! ;-)

Many thanks,
Oliver

> ---
>   drivers/net/can/Kconfig      | 4 ++--
>   drivers/net/can/Makefile     | 2 +-
>   drivers/net/can/dev/Makefile | 5 ++---
>   net/can/Kconfig              | 1 -
>   4 files changed, 5 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/net/can/Kconfig b/drivers/net/can/Kconfig
> index e15e320db476..bc074218d0ee 100644
> --- a/drivers/net/can/Kconfig
> +++ b/drivers/net/can/Kconfig
> @@ -1,7 +1,7 @@
>   # SPDX-License-Identifier: GPL-2.0-only
>   
>   menuconfig CAN_DEV
> -	tristate "CAN Device Drivers"
> +	bool "CAN Device Drivers"
>   	default y
>   	depends on CAN
>   	help
> @@ -20,7 +20,7 @@ menuconfig CAN_DEV
>   	  To compile as a module, choose M here: the module will be called
>   	  can-dev.
>   
> -if CAN_DEV
> +if CAN_DEV && CAN
>   
>   config CAN_VCAN
>   	tristate "Virtual Local CAN Interface (vcan)"
> diff --git a/drivers/net/can/Makefile b/drivers/net/can/Makefile
> index d7bc10a6b8ea..37e2f1a2faec 100644
> --- a/drivers/net/can/Makefile
> +++ b/drivers/net/can/Makefile
> @@ -7,7 +7,7 @@ obj-$(CONFIG_CAN_VCAN)		+= vcan.o
>   obj-$(CONFIG_CAN_VXCAN)		+= vxcan.o
>   obj-$(CONFIG_CAN_SLCAN)		+= slcan/
>   
> -obj-y				+= dev/
> +obj-$(CONFIG_CAN_DEV)		+= dev/
>   obj-y				+= esd/
>   obj-y				+= rcar/
>   obj-y				+= rockchip/
> diff --git a/drivers/net/can/dev/Makefile b/drivers/net/can/dev/Makefile
> index 633687d6b6c0..64226acf0f3d 100644
> --- a/drivers/net/can/dev/Makefile
> +++ b/drivers/net/can/dev/Makefile
> @@ -1,9 +1,8 @@
>   # SPDX-License-Identifier: GPL-2.0
>   
> -obj-$(CONFIG_CAN_DEV) += can-dev.o
> -
> -can-dev-y += skb.o
> +obj-$(CONFIG_CAN) += can-dev.o
>   
> +can-dev-$(CONFIG_CAN_DEV) += skb.o
>   can-dev-$(CONFIG_CAN_CALC_BITTIMING) += calc_bittiming.o
>   can-dev-$(CONFIG_CAN_NETLINK) += bittiming.o
>   can-dev-$(CONFIG_CAN_NETLINK) += dev.o
> diff --git a/net/can/Kconfig b/net/can/Kconfig
> index e4ccf731a24c..af64a6f76458 100644
> --- a/net/can/Kconfig
> +++ b/net/can/Kconfig
> @@ -5,7 +5,6 @@
>   
>   menuconfig CAN
>   	tristate "CAN bus subsystem support"
> -	select CAN_DEV
>   	help
>   	  Controller Area Network (CAN) is a slow (up to 1Mbit/s) serial
>   	  communications protocol. Development of the CAN bus started in