dfu: add DFU virtual backend

Add a virtual DFU backend to allow board specific read and write
(for OTP update for example).

Acked-by: Lukasz Majewski <lukma@denx.de>
Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
diff --git a/drivers/dfu/Kconfig b/drivers/dfu/Kconfig
index 1e1dff3..9fe5bc0 100644
--- a/drivers/dfu/Kconfig
+++ b/drivers/dfu/Kconfig
@@ -60,5 +60,12 @@
 	help
 	  This option enables using DFU to read and write to on any MTD device.
 
+config DFU_VIRT
+	bool "VIRTUAL flash back end for DFU"
+	help
+	  This option enables using DFU to read and write to VIRTUAL device
+	  used at board level to manage specific behavior
+	  (OTP update for example).
+
 endif
 endmenu
diff --git a/drivers/dfu/Makefile b/drivers/dfu/Makefile
index ebb119f..0d7925c 100644
--- a/drivers/dfu/Makefile
+++ b/drivers/dfu/Makefile
@@ -10,3 +10,4 @@
 obj-$(CONFIG_$(SPL_)DFU_RAM) += dfu_ram.o
 obj-$(CONFIG_$(SPL_)DFU_SF) += dfu_sf.o
 obj-$(CONFIG_$(SPL_)DFU_TFTP) += dfu_tftp.o
+obj-$(CONFIG_$(SPL_)DFU_VIRT) += dfu_virt.o
diff --git a/drivers/dfu/dfu.c b/drivers/dfu/dfu.c
index 4f4a07b7..2697235 100644
--- a/drivers/dfu/dfu.c
+++ b/drivers/dfu/dfu.c
@@ -474,6 +474,9 @@
 	} else if (strcmp(interface, "sf") == 0) {
 		if (dfu_fill_entity_sf(dfu, devstr, s))
 			return -1;
+	} else if (strcmp(interface, "virt") == 0) {
+		if (dfu_fill_entity_virt(dfu, devstr, s))
+			return -1;
 	} else {
 		printf("%s: Device %s not (yet) supported!\n",
 		       __func__,  interface);
@@ -569,7 +572,7 @@
 const char *dfu_get_dev_type(enum dfu_device_type t)
 {
 	const char *const dev_t[] = {NULL, "eMMC", "OneNAND", "NAND", "RAM",
-				     "SF", "MTD"};
+				     "SF", "MTD", "VIRT"};
 	return dev_t[t];
 }
 
diff --git a/drivers/dfu/dfu_virt.c b/drivers/dfu/dfu_virt.c
new file mode 100644
index 0000000..ea8c71f
--- /dev/null
+++ b/drivers/dfu/dfu_virt.c
@@ -0,0 +1,49 @@
+// SPDX-License-Identifier: GPL-2.0+ OR BSD-3-Clause
+/*
+ * Copyright (C) 2019, STMicroelectronics - All Rights Reserved
+ */
+#include <common.h>
+#include <dfu.h>
+#include <errno.h>
+#include <malloc.h>
+
+int __weak dfu_write_medium_virt(struct dfu_entity *dfu, u64 offset,
+				 void *buf, long *len)
+{
+	debug("%s: off=0x%llx, len=0x%x\n", __func__, offset, (u32)*len);
+
+	return 0;
+}
+
+int __weak dfu_get_medium_size_virt(struct dfu_entity *dfu, u64 *size)
+{
+	*size = 0;
+
+	return 0;
+}
+
+int __weak dfu_read_medium_virt(struct dfu_entity *dfu, u64 offset,
+				void *buf, long *len)
+{
+	debug("%s: off=0x%llx, len=0x%x\n", __func__, offset, (u32)*len);
+	*len = 0;
+
+	return 0;
+}
+
+int dfu_fill_entity_virt(struct dfu_entity *dfu, char *devstr, char *s)
+{
+	debug("%s: devstr = %s\n", __func__, devstr);
+
+	dfu->dev_type = DFU_DEV_VIRT;
+	dfu->layout = DFU_RAW_ADDR;
+	dfu->data.virt.dev_num = simple_strtoul(devstr, NULL, 10);
+
+	dfu->write_medium = dfu_write_medium_virt;
+	dfu->get_medium_size = dfu_get_medium_size_virt;
+	dfu->read_medium = dfu_read_medium_virt;
+
+	dfu->inited = 0;
+
+	return 0;
+}