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

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Message-ID: <5de9b33e-6129-4765-95a7-e3e12de1f8cd@kernel.org>
Date: Fri, 5 Dec 2025 00:30:14 +0100
From: Vincent Mailhol <mailhol@...nel.org>
To: Arnd Bergmann <arnd@...nel.org>, Marc Kleine-Budde <mkl@...gutronix.de>,
 Oliver Hartkopp <socketcan@...tkopp.net>
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

Hi Arnd,

Thanks for the fix!

On 04/12/2025 at 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>
> ---
>  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
                                  ^^^^^^^^
After this change, it is not possible to "choose M" for CAN_DEV anymore. I would
suggest to modify (or remove) the above sentence.

>  	  can-dev.> -if CAN_DEV
> +if CAN_DEV && CAN
              ^^^^^^
Is this needed? CAN_DEV depends on CAN, so the condition

  CAN_DEV && !CAN

should not be reachable.

>  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


Yours sincerely,
Vincent Mailhol