checkpoints: do not use SOF_TEST_INTERVAL in test _iterations_

The purpose of SOF_TEST_INTERVAL is to avoid log gaps between tests,
_not_ between test iterations of the same test.

Fixes issue where the (recent) check-kmod-load-unload.sh was catching
_multiple_ firmware boots, including boots from previous test
iterations, example:

sof-test/test-case/check-mod-load-unload.sh -l 50

Polling 'sof_firmware_boot_complete --since=@1646100584' every 1s for 10s
[ 2968.155103] kernel: sof-audio-pci-intel-tgl 0000:00:1f.3: firmware boot complete
[ 2970.706560] kernel: sof-audio-pci-intel-tgl 0000:00:1f.3: firmware boot complete
[ 2974.522111] kernel: sof-audio-pci-intel-tgl 0000:00:1f.3: firmware boot complete
Completed 'sof_firmware_boot_complete --since=@1646100584' after 0s and 1 attempts

This may fix other, similar tests too.

Signed-off-by: Marc Herbert <marc.herbert@intel.com>

Author: marc-hb

case-lib/hijack.sh

@@ -86,6 +86,8 @@ function func_exit_handler()
     fi
 
     if [[ "$KERNEL_CHECKPOINT" =~ ^[0-9]{10} ]]; then
+        # Do not collect the entire duration of the test but only the
+        # last iteration.
         journalctl_cmd --since=@"$KERNEL_CHECKPOINT" > "$LOG_ROOT/dmesg.txt"
     elif [[ "$KERNEL_CHECKPOINT" == "disabled" ]]; then
         journalctl_cmd > "$LOG_ROOT/dmesg.txt"

case-lib/lib.sh

@@ -82,7 +82,14 @@ setup_kernel_check_point()
     # appear in the next one, see comments in config.sh.  Add 3 extra
     # second to account for our own, sof-test delays after PASS/FAIL
     # decision: time spent collecting logs etc.
-    KERNEL_CHECKPOINT=$(($(date +%s) - SOF_TEST_INTERVAL - 3))
+    if [ -z "$KERNEL_CHECKPOINT" ]; then
+        KERNEL_CHECKPOINT=$(($(date +%s) - SOF_TEST_INTERVAL - 3))
+    else
+        # Not the first time we are called so this is a test
+        # _iteration_. Add just one extra second in case a test makes
+        # the mistake to call this function _after_ checking the logs.
+        KERNEL_CHECKPOINT=$(($(date +%s) - 1))
+    fi
 }
 
 # This function adds a fake error to dmesg (which is always saved by
@@ -425,6 +432,8 @@ journalctl_cmd()
      --no-hostname "$@"
 }
 
+# Force the exit handler to collect all the logs since boot time instead
+# of just the last test iteration.
 disable_kernel_check_point()
 {
     KERNEL_CHECKPOINT="disabled"