[PATCH] spi: spidev_test: Warn when the mode is not the requested mode

[David Fries <David@fries.net>]

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>
---
This is the kernel log, I just didn't see it at first.
spidev spi1.0: setup: ignoring unsupported mode bits 200

I was testing --quad on a Raspberry Pi where I didn't expect it to
work, which the ioctl didn't return an error, it just cleared the bits
it didn't support.

 tools/spi/spidev_test.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/tools/spi/spidev_test.c b/tools/spi/spidev_test.c
index 83844f8b862a..5629387bfc56 100644
--- a/tools/spi/spidev_test.c
+++ b/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
-- 
2.30.2