[bug report] HID: pidff: Add support for AXES_ENABLE field

[Dan Carpenter <dan.carpenter@linaro.org>]

Hello Tomasz Pakuła,

This is a semi-automatic email about new static checker warnings.

Commit 1d72e7bd340b ("HID: pidff: Add support for AXES_ENABLE field")
from Aug 13, 2025, leads to the following Smatch complaint:

    drivers/hid/usbhid/hid-pidff.c:1308 pidff_find_special_fields()
    error: we previously assumed 'pidff->axes_enable' could be null (see line 1302)

    drivers/hid/usbhid/hid-pidff.c:1322 pidff_find_special_fields()
    warn: variable dereferenced before check 'pidff->axes_enable' (see line 1308)

drivers/hid/usbhid/hid-pidff.c
  1295          if (PIDFF_FIND_SPECIAL_KEYS(operation_id, effect_operation_status,
  1296                                      effect_operation_status) !=
  1297              ARRAY_SIZE(pidff_effect_operation_status)) {
  1298                  hid_err(pidff->hid, "effect operation identifiers not found\n");
  1299                  return -1;
  1300          }
  1301  
  1302          if (!pidff->axes_enable)
                     ^^^^^^^^^^^^^^^^^^
This assumes pidff->axes_enable can be NULL

  1303                  hid_info(pidff->hid, "axes enable field not found!\n");
  1304          else
  1305                  hid_dbg(pidff->hid, "axes enable report count: %u\n",
  1306                          pidff->axes_enable->report_count);
  1307  
  1308          uint found = PIDFF_FIND_GENERAL_DESKTOP(direction_axis_id, axes_enable,
  1309                                                  direction_axis);

But the PIDFF_FIND_GENERAL_DESKTOP() function dereferences it without
checking so if it's NULL then it will crash.

  1310  
  1311          pidff->axis_count = found;
  1312          hid_dbg(pidff->hid, "found direction axes: %u", found);
  1313  
  1314          for (int i = 0; i < sizeof(pidff_direction_axis); i++) {
  1315                  if (!pidff->direction_axis_id[i])
  1316                          continue;
  1317  
  1318                  hid_dbg(pidff->hid, "axis %d, usage: 0x%04x, index: %d", i + 1,
  1319                          pidff_direction_axis[i], pidff->direction_axis_id[i]);
  1320          }
  1321  
  1322          if (pidff->axes_enable && found != pidff->axes_enable->report_count)
                    ^^^^^^^^^^^^^^^^^^
Checked for NULL again.

  1323                  hid_warn(pidff->hid, "axes_enable: %u != direction axes: %u",
  1324                           pidff->axes_enable->report_count, found);

regards,
dan carpenter