fpga manager: xilinx-spi: provide better diagnostics on programming failure

When the DONE pin does not go high after programming to confirm programming
success, the INIT_B pin provides some info on the reason. Use it if
available to provide a more explanatory error message.
Reviewed-by: Tom Rix <trix@redhat.com>
Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net>
Signed-off-by: Moritz Fischer <mdf@kernel.org>

drivers/fpga/xilinx-spi.c

@@ -195,7 +195,21 @@ static int xilinx_spi_write_complete(struct fpga_manager *mgr,
 			return 0;
 	}
 
-	dev_err(&mgr->dev, "Timeout after config data transfer\n");
+	if (conf->init_b) {
+		ret = gpiod_get_value(conf->init_b);
+
+		if (ret < 0) {
+			dev_err(&mgr->dev, "Error reading INIT_B (%d)\n", ret);
+			return ret;
+		}
+
+		dev_err(&mgr->dev,
+			ret ? "CRC error or invalid device\n"
+			: "Missing sync word or incomplete bitstream\n");
+	} else {
+		dev_err(&mgr->dev, "Timeout after config data transfer\n");
+	}
+
 	return -ETIMEDOUT;
 }