Re: [PATCH 11/21] can: netlink: add can_dtb_changelink()

[kernel test robot <lkp@intel.com>]

Hi Vincent,

kernel test robot noticed the following build warnings:

[auto build test WARNING on 2fd4161d0d2547650d9559d57fc67b4e0a26a9e3]

url:    https://github.com/intel-lab-lkp/linux/commits/Vincent-Mailhol/can-dev-move-struct-data_bittiming_params-to-linux-can-bittiming-h/20250903-170807
base:   2fd4161d0d2547650d9559d57fc67b4e0a26a9e3
patch link:    https://lore.kernel.org/r/20250903-canxl-netlink-prep-v1-11-904bd6037cd9%40kernel.org
patch subject: [PATCH 11/21] can: netlink: add can_dtb_changelink()
config: x86_64-kexec (https://download.01.org/0day-ci/archive/20250905/202509050404.ZLQknagH-lkp@intel.com/config)
compiler: clang version 20.1.8 (https://github.com/llvm/llvm-project 87f0227cb60147a26a1eeb4fb06e3b505e9c7261)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250905/202509050404.ZLQknagH-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/202509050404.ZLQknagH-lkp@intel.com/

All warnings (new ones prefixed by >>):

   drivers/net/can/dev/netlink.c:111:6: warning: variable 'is_on' is used uninitialized whenever 'if' condition is false [-Wsometimes-uninitialized]
     111 |         if (ifla_can_data_bittiming == IFLA_CAN_DATA_BITTIMING) {
         |             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   drivers/net/can/dev/netlink.c:119:6: note: uninitialized use occurs here
     119 |         if (is_on) {
         |             ^~~~~
   drivers/net/can/dev/netlink.c:111:2: note: remove the 'if' if its condition is always true
     111 |         if (ifla_can_data_bittiming == IFLA_CAN_DATA_BITTIMING) {
         |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     112 |                 data_tdc = data[IFLA_CAN_TDC];
     113 |                 tdc_flags = flags & CAN_CTRLMODE_FD_TDC_MASK;
     114 |                 is_on = flags & CAN_CTRLMODE_FD;
     115 |         } else {
         |           ~~~~~~
     116 |                 WARN_ON(1); /* Place holder for CAN XL */
         |                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     117 |         }
         |         ~
   drivers/net/can/dev/netlink.c:108:12: note: initialize the variable 'is_on' to silence this warning
     108 |         bool is_on;
         |                   ^
         |                    = 0
>> drivers/net/can/dev/netlink.c:227:6: warning: variable 'data_bittiming' is used uninitialized whenever 'if' condition is false [-Wsometimes-uninitialized]
     227 |         if (fd) {
         |             ^~
   drivers/net/can/dev/netlink.c:236:7: note: uninitialized use occurs here
     236 |         if (!data_bittiming)
         |              ^~~~~~~~~~~~~~
   drivers/net/can/dev/netlink.c:227:2: note: remove the 'if' if its condition is always true
     227 |         if (fd) {
         |         ^~~~~~~
     228 |                 data_bittiming = data[IFLA_CAN_DATA_BITTIMING];
     229 |                 data_tdc = data[IFLA_CAN_TDC];
     230 |                 dbt_params = &priv->fd;
     231 |                 tdc_mask = CAN_CTRLMODE_FD_TDC_MASK;
     232 |         } else {
         |           ~~~~~~
     233 |                 WARN_ON(1); /* Place holder for CAN XL */
         |                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     234 |         }
         |         ~
   drivers/net/can/dev/netlink.c:219:31: note: initialize the variable 'data_bittiming' to silence this warning
     219 |         struct nlattr *data_bittiming, *data_tdc;
         |                                      ^
         |                                       = NULL
   2 warnings generated.


vim +227 drivers/net/can/dev/netlink.c

   215	
   216	static int can_dbt_changelink(struct net_device *dev, struct nlattr *data[],
   217				      bool fd, struct netlink_ext_ack *extack)
   218	{
   219		struct nlattr *data_bittiming, *data_tdc;
   220		struct can_priv *priv = netdev_priv(dev);
   221		struct data_bittiming_params *dbt_params;
   222		struct can_bittiming dbt;
   223		bool need_tdc_calc = false;
   224		u32 tdc_mask;
   225		int err;
   226	
 > 227		if (fd) {
   228			data_bittiming = data[IFLA_CAN_DATA_BITTIMING];
   229			data_tdc = data[IFLA_CAN_TDC];
   230			dbt_params = &priv->fd;
   231			tdc_mask = CAN_CTRLMODE_FD_TDC_MASK;
   232		} else {
   233			WARN_ON(1); /* Place holder for CAN XL */
   234		}
   235	
   236		if (!data_bittiming)
   237			return 0;
   238	
   239		/* Do not allow changing bittiming while running */
   240		if (dev->flags & IFF_UP)
   241			return -EBUSY;
   242	
   243		/* Calculate bittiming parameters based on data_bittiming_const
   244		 * if set, otherwise pass bitrate directly via do_set_bitrate().
   245		 * Bail out if neither is given.
   246		 */
   247		if (!dbt_params->data_bittiming_const && !dbt_params->do_set_data_bittiming &&
   248		    !dbt_params->data_bitrate_const)
   249			return -EOPNOTSUPP;
   250	
   251		memcpy(&dbt, nla_data(data_bittiming), sizeof(dbt));
   252		err = can_get_bittiming(dev, &dbt, dbt_params->data_bittiming_const,
   253					dbt_params->data_bitrate_const,
   254					dbt_params->data_bitrate_const_cnt, extack);
   255		if (err)
   256			return err;
   257	
   258		if (priv->bitrate_max && dbt.bitrate > priv->bitrate_max) {
   259			NL_SET_ERR_MSG_FMT(extack,
   260					   "CAN data bitrate %u bps surpasses transceiver capabilities of %u bps",
   261					   dbt.bitrate, priv->bitrate_max);
   262			return -EINVAL;
   263		}
   264	
   265		memset(&dbt_params->tdc, 0, sizeof(dbt_params->tdc));
   266		if (data[IFLA_CAN_CTRLMODE]) {
   267			struct can_ctrlmode *cm = nla_data(data[IFLA_CAN_CTRLMODE]);
   268	
   269			need_tdc_calc = !(cm->mask & tdc_mask);
   270		}
   271		if (data_tdc) {
   272			/* TDC parameters are provided: use them */
   273			err = can_tdc_changelink(dbt_params, data_tdc, extack);
   274			if (err) {
   275				priv->ctrlmode &= ~tdc_mask;
   276				return err;
   277			}
   278		} else if (need_tdc_calc) {
   279			/* Neither of TDC parameters nor TDC flags are provided:
   280			 * do calculation
   281			 */
   282			can_calc_tdco(&dbt_params->tdc, dbt_params->tdc_const, &dbt,
   283				      &priv->ctrlmode, priv->ctrlmode_supported);
   284		} /* else: both CAN_CTRLMODE_TDC_{AUTO,MANUAL} are explicitly
   285		   * turned off. TDC is disabled: do nothing
   286		   */
   287	
   288		memcpy(&dbt_params->data_bittiming, &dbt, sizeof(dbt));
   289	
   290		if (dbt_params->do_set_data_bittiming) {
   291			/* Finally, set the bit-timing registers */
   292			err = dbt_params->do_set_data_bittiming(dev);
   293			if (err)
   294				return err;
   295		}
   296	
   297		return 0;
   298	}
   299	

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