am7xxx: split declaration and initialization of the "transferred" variable

[libam7xxx.git] / src / am7xxx.c

diff --git a/src/am7xxx.c b/src/am7xxx.c
index 3ba56f3..d619f89 100644 (file)
--- a/src/am7xxx.c
+++ b/src/am7xxx.c
@@ -381,8 +381,9 @@ static void trace_dump_buffer(am7xxx_context *ctx, const char *message,
 static int read_data(am7xxx_device *dev, uint8_t *buffer, unsigned int len)
 {
        int ret;
-       int transferred = 0;
+       int transferred;
 
+       transferred = 0;
        ret = libusb_bulk_transfer(dev->usb_device, 0x81, buffer, len, &transferred, 0);
        if (ret != 0 || (unsigned int)transferred != len) {
                error(dev->ctx, "%s. Transferred: %d (expected %u)\n",
@@ -398,10 +399,11 @@ static int read_data(am7xxx_device *dev, uint8_t *buffer, unsigned int len)
 static int send_data(am7xxx_device *dev, uint8_t *buffer, unsigned int len)
 {
        int ret;
-       int transferred = 0;
+       int transferred;
 
        trace_dump_buffer(dev->ctx, "sending -->", buffer, len);
 
+       transferred = 0;
        ret = libusb_bulk_transfer(dev->usb_device, 0x1, buffer, len, &transferred, 0);
        if (ret != 0 || (unsigned int)transferred != len) {
                error(dev->ctx, "%s. Transferred: %d (expected %u)\n",
@@ -744,13 +746,24 @@ static int open_device(am7xxx_context *ctx,
 
        if (current_configuration != (*dev)->desc->configuration) {
                /*
-                * In principle kernel drivers bound to each interface should
-                * be detached before setting the configuration, but in
-                * practice this is not necessary for most devices.
+                * In principle, before setting a new configuration, kernel
+                * drivers should be detached from _all_ interfaces; for
+                * example calling something like the following "invented"
+                * function _before_ setting the new configuration:
                 *
-                * For example something like the following function would be
-                * called:
-                *      libusb_detach_all_kernel_drivers((*dev)->usb_device);
+                *   libusb_detach_all_kernel_drivers((*dev)->usb_device);
+                *
+                * However, in practice, this is not necessary for most
+                * devices as they have only one configuration.
+                *
+                * When a device only has one configuration:
+                *
+                *   - if there was a kernel driver bound to the device, it
+                *     had already set the configuration and the call below
+                *     will be skipped;
+                *
+                *   - if no kernel driver was bound to the device, the call
+                *     below will suceed.
                 */
                ret = libusb_set_configuration((*dev)->usb_device,
                                               (*dev)->desc->configuration);
@@ -1090,8 +1103,10 @@ AM7XXX_PUBLIC int am7xxx_init(am7xxx_context **ctx)
        (*ctx)->log_level = AM7XXX_LOG_TRACE;
 
        ret = libusb_init(&((*ctx)->usb_context));
-       if (ret < 0)
+       if (ret < 0) {
+               error(*ctx, "libusb_init failed: %s\n", libusb_error_name(ret));
                goto out_free_context;
+       }
 
        libusb_set_debug((*ctx)->usb_context, LIBUSB_LOG_LEVEL_INFO);