greatfet: don't print misleading "unknown" libusb error text

Only lookup libusb error messages for negative return values which
communicate error codes. Positive return values are transmission counts
and are not an error.

The "UNKNOWN" messages only were seen at higher log levels. Users were
not affected by the issue.

diff --git a/src/hardware/greatfet/protocol.c b/src/hardware/greatfet/protocol.c
index 913f981c1f01e33cfba06159f5d228c68ff0a408..0c6c6c4ea60a208af0ed710a9e4dd9b78a892f28 100644 (file)
--- a/src/hardware/greatfet/protocol.c
+++ b/src/hardware/greatfet/protocol.c
@@ -169,7 +169,7 @@ static int greatfet_ctrl_out_in(const struct sr_dev_inst *sdi,
                flags, (void *)tx_data, tx_size, timeout_ms);
        if (sr_log_loglevel_get() >= SR_LOG_SPEW) {
                const char *msg;
-               msg = ret ? libusb_error_name(ret) : "-";
+               msg = ret < 0 ? libusb_error_name(ret) : "-";
                sr_spew("USB out, rc %d, %s", ret, msg);
        }
        if (ret < 0) {
@@ -197,7 +197,7 @@ static int greatfet_ctrl_out_in(const struct sr_dev_inst *sdi,
                0, rx_data, rx_size, timeout_ms);
        if (sr_log_loglevel_get() >= SR_LOG_SPEW) {
                const char *msg;
-               msg = ret ? libusb_error_name(ret) : "-";
+               msg = ret < 0 ? libusb_error_name(ret) : "-";
                sr_spew("USB in, rc %d, %s", ret, msg);
        }
        if (ret < 0) {