spi: spidev_test: Warn when the mode is not the requested mode

Print a warning if the device mode doesn't match the requested mode.
The user doesn't enter the mode in hex so it isn't obvious when
setting the mode succeeds that the mode isn't the requested mode.  The
kernel logs a message, it will be more visible if the test also prints
a warning.  I was testing --quad, which is unsupported, but doesn't
cause the mode request to fail.
Signed-off-by: David Fries <David@Fries.net>
Link: https://lore.kernel.org/r/YqbNnSGtWHe/GG7w@spacedout.fries.netSigned-off-by: Mark Brown <broonie@kernel.org>

tools/spi/spidev_test.c

@@ -417,6 +417,7 @@ int main(int argc, char *argv[])
 {
 	int ret = 0;
 	int fd;
+	uint32_t request;
 
 	parse_opts(argc, argv);
 
@@ -430,13 +431,23 @@ int main(int argc, char *argv[])
 	/*
 	 * spi mode
 	 */
+	/* WR is make a request to assign 'mode' */
+	request = mode;
 	ret = ioctl(fd, SPI_IOC_WR_MODE32, &mode);
 	if (ret == -1)
 		pabort("can't set spi mode");
 
+	/* RD is read what mode the device actually is in */
 	ret = ioctl(fd, SPI_IOC_RD_MODE32, &mode);
 	if (ret == -1)
 		pabort("can't get spi mode");
+	/* Drivers can reject some mode bits without returning an error.
+	 * Read the current value to identify what mode it is in, and if it
+	 * differs from the requested mode, warn the user.
+	 */
+	if (request != mode)
+		printf("WARNING device does not support requested mode 0x%x\n",
+			request);
 
 	/*
 	 * bits per word