usb: Only set configuration when needed

Setting the USB configurations triggers a soft reset on most devices, thus it
should be avoided as much as possible.

In particular, this allows running multiple commands in a row.

Signed-off-by: Paul Kocialkowski <contact@paulk.fr>

1 files changed, 12 insertions, 3 deletions

diff --git a/src/usb.c b/src/usb.c
index 8631c06..5742d7b 100644
--- a/src/usb.c
+++ b/src/usb.c
@@ -27,6 +27,7 @@
 int usb_open(struct context *context)
 {
 	struct libusb_device_handle *handle;
+	int configuration;
 	int rc;
 
 	if (context == NULL)
@@ -34,7 +35,7 @@ int usb_open(struct context *context)
 
 	rc = libusb_init(NULL);
 	if (rc < 0) {
-		fprintf(stderr, "Initializing libusb failed\n");
+		fprintf(stderr, "Initializing USB failed\n");
 		return -1;
 	}
 
@@ -47,12 +48,20 @@ int usb_open(struct context *context)
 
 	libusb_detach_kernel_driver(handle, USB_INTERFACE);
 
-	rc = libusb_set_configuration(handle, USB_CONFIGURATION);
+	rc = libusb_get_configuration(handle, &configuration);
 	if (rc < 0) {
-		fprintf(stderr, "Setting USB configuration failed\n");
+		fprintf(stderr, "Getting USB configuration failed\n");
 		goto error;
 	}
 
+	if (configuration != USB_CONFIGURATION) {
+		rc = libusb_set_configuration(handle, USB_CONFIGURATION);
+		if (rc < 0) {
+			fprintf(stderr, "Setting USB configuration failed\n");
+			goto error;
+		}
+	}
+
 	rc = libusb_claim_interface(handle, USB_INTERFACE);
 	if (rc < 0) {
 		fprintf(stderr, "Claiming USB interface failed\n");