selftests: firmware: Use smaller dictionary for XZ compression

The xz -9 option leads to an unnecessarily too large dictionary that
isn't really suitable for the kernel firmware loader.  Pass the
dictionary size explicitly, instead.

While we're at it, make the xz command call defined in $RUN_XZ for
simplicity.

Fixes: 108ae07c ("selftests: firmware: Add compressed firmware tests")
Signed-off-by: NTakashi Iwai <tiwai@suse.de>
Link: https://lore.kernel.org/r/20220421152908.4718-3-tiwai@suse.deSigned-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

tools/testing/selftests/firmware/fw_filesystem.sh

@@ -11,6 +11,8 @@ TEST_REQS_FW_SET_CUSTOM_PATH="yes"
 TEST_DIR=$(dirname $0)
 source $TEST_DIR/fw_lib.sh
 
+RUN_XZ="xz -C crc32 --lzma2=dict=2MiB"
+
 check_mods
 check_setup
 verify_reqs
@@ -410,9 +412,9 @@ test_request_firmware_nowait_custom()
 	RANDOM_FILE_PATH=$(setup_random_file)
 	RANDOM_FILE="$(basename $RANDOM_FILE_PATH)"
 	if [ "$2" = "both" ]; then
-		xz -9 -C crc32 -k $RANDOM_FILE_PATH
+		$RUN_XZ -k $RANDOM_FILE_PATH
 	elif [ "$2" = "xzonly" ]; then
-		xz -9 -C crc32 $RANDOM_FILE_PATH
+		$RUN_XZ $RANDOM_FILE_PATH
 	fi
 	config_set_name $RANDOM_FILE
 	config_trigger_async
@@ -501,7 +503,7 @@ test_request_partial_firmware_into_buf_nofile 2 10
 test "$HAS_FW_LOADER_COMPRESS" != "yes" && exit 0
 
 # test with both files present
-xz -9 -C crc32 -k $FW
+$RUN_XZ -k $FW
 config_set_name $NAME
 echo
 echo "Testing with both plain and xz files present..."