spi: spidev_test: add support for word delay

Support setting the word delay using the -w/--word-delay command line
parameter. Note that spidev exposes word delay only as an u8, allowing
for a maximum of 255us of delay to be inserted.

Signed-off-by: Jonas Rebmann <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Mark Brown <[e-mail]>

tools/spi/spidev_test.c

···
 static char *output_file;
 static uint32_t speed = 500000;
 static uint16_t delay;
+static uint16_t word_delay;
 static int verbose;
 static int transfer_size;
 static int iterations;
···
 		.rx_buf = (unsigned long)rx,
 		.len = len,
 		.delay_usecs = delay,
+		.word_delay_usecs = word_delay,
 		.speed_hz = speed,
 		.bits_per_word = bits,
 	};
···
 
 static void print_usage(const char *prog)
 {
-	printf("Usage: %s [-2348CDFHILMNORSZbdilopsv]\n", prog);
+	printf("Usage: %s [-2348CDFHILMNORSZbdilopsvw]\n", prog);
 	puts("general device settings:\n"
 		 "  -D --device         device to use (default /dev/spidev1.1)\n"
 		 "  -s --speed          max speed (Hz)\n"
 		 "  -d --delay          delay (usec)\n"
+		 "  -w --word-delay     word delay (usec)\n"
 		 "  -l --loop           loopback\n"
 		 "spi mode:\n"
 		 "  -H --cpha           clock phase\n"
···
 			{ "device",        1, 0, 'D' },
 			{ "speed",         1, 0, 's' },
 			{ "delay",         1, 0, 'd' },
+			{ "word-delay",    1, 0, 'w' },
 			{ "loop",          0, 0, 'l' },
 			{ "cpha",          0, 0, 'H' },
 			{ "cpol",          0, 0, 'O' },
···
 		};
 		int c;
 
-		c = getopt_long(argc, argv, "D:s:d:b:i:o:lHOLC3ZFMNR248p:vS:I:",
+		c = getopt_long(argc, argv, "D:s:d:w:b:i:o:lHOLC3ZFMNR248p:vS:I:",
 				lopts, NULL);
 
 		if (c == -1)
···
 			break;
 		case 'd':
 			delay = atoi(optarg);
+			break;
+		case 'w':
+			word_delay = atoi(optarg);
 			break;
 		case 'b':
 			bits = atoi(optarg);