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

[Vincent Mailhol <mailhol@kernel.org>]

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@intel.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 will first send a separate fix for can_calc_tdco() targeting
> net/main and send the v2 for this series once the can_calc_tdco() fix
> reaches net-next/main.

N.B. this issue does not impact the code when
CONFIG_CAN_CALC_BITTIMING is set. So you can continue to review while
this problem is getting addressed.


Yours sincerely,
Vincent Mailhol