dfu: tftp: update: Provide tftp support for the DFU subsystem

This commit adds initial support for using tftp for downloading and
upgrading firmware on the device.

Signed-off-by: Lukasz Majewski <l.majewski@majess.pl>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>
diff --git a/drivers/dfu/dfu_tftp.c b/drivers/dfu/dfu_tftp.c
new file mode 100644
index 0000000..cd71708
--- /dev/null
+++ b/drivers/dfu/dfu_tftp.c
@@ -0,0 +1,65 @@
+/*
+ * (C) Copyright 2015
+ * Lukasz Majewski <l.majewski@majess.pl>
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#include <common.h>
+#include <malloc.h>
+#include <errno.h>
+#include <dfu.h>
+
+int dfu_tftp_write(char *dfu_entity_name, unsigned int addr, unsigned int len,
+		   char *interface, char *devstring)
+{
+	char *s, *sb;
+	int alt_setting_num, ret;
+	struct dfu_entity *dfu;
+
+	debug("%s: name: %s addr: 0x%x len: %d device: %s:%s\n", __func__,
+	      dfu_entity_name, addr, len, interface, devstring);
+
+	ret = dfu_init_env_entities(interface, devstring);
+	if (ret)
+		goto done;
+
+	/*
+	 * We need to copy name pointed by *dfu_entity_name since this text
+	 * is the integral part of the FDT image.
+	 * Any implicit modification (i.e. done by strsep()) will corrupt
+	 * the FDT image and prevent other images to be stored.
+	 */
+	s = strdup(dfu_entity_name);
+	sb = s;
+	if (!s) {
+		ret = -ENOMEM;
+		goto done;
+	}
+
+	strsep(&s, "@");
+	debug("%s: image name: %s strlen: %d\n", __func__, sb, strlen(sb));
+
+	alt_setting_num = dfu_get_alt(sb);
+	free(sb);
+	if (alt_setting_num < 0) {
+		error("Alt setting [%d] to write not found!",
+		      alt_setting_num);
+		ret = -ENODEV;
+		goto done;
+	}
+
+	dfu = dfu_get_entity(alt_setting_num);
+	if (!dfu) {
+		error("DFU entity for alt: %d not found!", alt_setting_num);
+		ret = -ENODEV;
+		goto done;
+	}
+
+	ret = dfu_write_from_mem_addr(dfu, (void *)addr, len);
+
+done:
+	dfu_free_entities();
+
+	return ret;
+}