linux-kernel - Re: [PATCH 8/9] can: calc_bittiming: add PWM calculation

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Message-ID: <3067598f-9465-4544-a35f-6c09b5a8d4ad@kernel.org>
Date: Tue, 14 Oct 2025 11:32:04 +0900
From: Vincent Mailhol <mailhol@...nel.org>
To: kernel test robot <lkp@...el.com>, Marc Kleine-Budde
 <mkl@...gutronix.de>, Oliver Hartkopp <socketcan@...tkopp.net>
Cc: oe-kbuild-all@...ts.linux.dev,
 Stéphane Grosjean <stephane.grosjean@...-networks.com>,
 Robert Nawrath <mbro1689@...il.com>, Minh Le <minh.le.aj@...esas.com>,
 Duy Nguyen <duy.nguyen.rh@...esas.com>, linux-can@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 8/9] can: calc_bittiming: add PWM calculation

On 14/10/2025 at 11:19, Vincent Mailhol wrote:
> On 14/10/2025 at 11:05, Vincent Mailhol wrote:
>> On 14/10/2025 at 06:21, kernel test robot wrote:
>>> Hi Vincent,
>>>
>>> kernel test robot noticed the following build warnings:
>>>
>>> [auto build test WARNING on cb6649f6217c0331b885cf787f1d175963e2a1d2]
>>>
>>> url:    https://github.com/intel-lab-lkp/linux/commits/Vincent-Mailhol/can-dev-can_dev_dropped_skb-drop-CAN-FD-skbs-if-FD-is-off/20251013-191232
>>> base:   cb6649f6217c0331b885cf787f1d175963e2a1d2
>>> patch link:    https://lore.kernel.org/r/20251013-canxl-netlink-v1-8-f422b7e2729f%40kernel.org
>>> patch subject: [PATCH 8/9] can: calc_bittiming: add PWM calculation
>>> config: riscv-randconfig-001-20251014 (https://download.01.org/0day-ci/archive/20251014/202510140553.qo3f0I9s-lkp@intel.com/config)
>>> compiler: riscv64-linux-gcc (GCC) 10.5.0
>>> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20251014/202510140553.qo3f0I9s-lkp@intel.com/reproduce)
>>>
>>> If you fix the issue in a separate patch/commit (i.e. not just a new version of
>>> the same patch/commit), kindly add following tags
>>> | Reported-by: kernel test robot <lkp@...el.com>
>>> | Closes: https://lore.kernel.org/oe-kbuild-all/202510140553.qo3f0I9s-lkp@intel.com/
>>>
>>> All warnings (new ones prefixed by >>):
>>>
>>>    In file included from include/linux/can/dev.h:18,
>>>                     from net/can/raw.c:53:
>>>    include/linux/can/bittiming.h: In function 'can_calc_pwm':
>>>>> include/linux/can/bittiming.h:204:1: warning: no return statement in function returning non-void [-Wreturn-type]
>>>      204 | }
>>>          | ^
>>>
>>> Kconfig warnings: (for reference only)
>>>    WARNING: unmet direct dependencies detected for ARCH_HAS_ELF_CORE_EFLAGS
>>>    Depends on [n]: BINFMT_ELF [=y] && ELF_CORE [=n]
>>>    Selected by [y]:
>>>    - RISCV [=y]
>>>
>>>
>>> vim +204 include/linux/can/bittiming.h
>>>
>>>    200	
>>>    201	static inline int
>>>    202	can_calc_pwm(struct net_device *dev, struct netlink_ext_ack *extack)
>>>    203	{
>>>  > 204	}
>>>    205	#endif /* CONFIG_CAN_CALC_BITTIMING */
>>>    206	
>>
>> I see, this only occurs if CONFIG_CAN_CALC_BITTIMING is not set.
>>
>> What is surprising enough is that can_calc_tdco() has the exact same
>> issue but we never received a report.
> 
> Actually, can_calc_tdco() is not getting a warning because it returns
> void. But this doesn't change the fact that it should be returning an
> error when CONFIG_CAN_CALC_BITTIMING is not set.

I spoke too quickly. can_calc_tdco() is only called when no TDC
parameters are provided. In that case, if CONFIG_CAN_CALC_BITTIMING is
not set, doing nothing is the correct approach. i.e. there is nothing
to fix here. So there will be no fix patch to net/main and I will
directly incorporate the fix in a v2.

Sorry for the noise!


Yours sincerely,
Vincent Mailhol