zephyr: Add support for devices without erase and reduced erases

Add Kconfig options:
  - CONFIG_MCUBOOT_STORAGE_WITHOUT_ERASE that enables MCUboot
    configuration MCUBOOT_SUPPORT_DEV_WITHOUT_ERASE
  - CONFIG_MCUBOOT_STORAGE_WITH_ERASE that enables MCUboot
    configuration MCUBOOT_SUPPORT_DEV_WITH_ERASE
  - CONFIG_MCUBOOT_STORAGE_MINIMAL_SCRAMBLE that enables MCUboot
    configuration MCUBOOT_MINIMAL_SCRAMBLE

Adds implementation of flash_area_erase_required, which is required when
MCUBOOT_STORAGE_DEV_WITHOUT_ERASE is enabled.

Signed-off-by: Dominik Ermel <dominik.ermel@nordicsemi.no>

boot/zephyr/Kconfig

@@ -838,6 +838,44 @@ endif # BOOT_DECOMPRESSION_SUPPORT
 
 endmenu
 
+config MCUBOOT_STORAGE_WITHOUT_ERASE
+	bool "Support for devices without erase"
+	depends on FLASH_HAS_NO_EXPLICIT_ERASE
+	help
+	  Not all devices require erase before write and, depending on driver,
+	  may emulate erase by write, as a way to scramble data rather then
+	  by hardware requirement. This unfortunately means that code that
+	  does erase before write, when not needed, will write device twice
+	  which not only reduces device life time but also doubles time
+	  of any write operation (one write for erase and one write for actual
+	  write).
+	  When this option is enabled, MCUboot will check for type of device
+	  and will avoid erase where not needed.
+
+# The depends on FLASH_HAS_EXPLICIT_ERASE is intentionlally missing for now
+# as so far Zephyr emulates erase on such devices anyway.
+config MCUBOOT_STORAGE_WITH_ERASE
+	bool "Support for devices with erase"
+	default y
+	help
+	  Support for devices with erase
+
+config MCUBOOT_STORAGE_MINIMAL_SCRAMBLE
+	bool "Do minimal required work to remove data"
+	help
+	  In some cases MCUboot has to remove data, which usually means make
+	  it non-viable for MCUboot rather then completely destroyed.
+	  For example when MCUboot does not want to bother with broken image
+	  in some slot it will remove it.
+	  The same can be achieved with just removal of header, leaving the
+	  rest of image untouched, as without header MCUboot will not be able
+	  to recognize image in slot as bootable.
+	  When this option is enabled, MCUboot will not attempt to erase
+	  entire slot or image, instead it will just remove enough of
+	  data from slot to not recognize it as image anymore.
+	  Depending on type of device this may be done by erase of minimal
+	  number of pages or overwrite of part of image.
+
 config MCUBOOT_DEVICE_SETTINGS
 	# Hidden selector for device-specific settings
 	bool

boot/zephyr/include/flash_map_backend/flash_map_backend.h

@@ -106,6 +106,23 @@ static inline uint32_t flash_sector_get_size(const struct flash_sector *fs)
 int flash_area_get_sector(const struct flash_area *fa, off_t off,
                           struct flash_sector *fs);
 
+
+#if defined(CONFIG_MCUBOOT)
+static inline bool flash_area_erase_required(const struct flash_area *fa)
+{
+#if defined(CONFIG_FLASH_HAS_EXPLICIT_ERASE) && defined(CONFIG_FLASH_HAS_NO_EXPLICIT_ERASE)
+    const struct flash_parameters *fp = flash_get_parameters(flash_area_get_device(fa));
+
+    return flash_params_get_erase_cap(flash_get_parameters(flash_area_get_device(fa))) &
+            FLASH_ERASE_C_EXPLICIT;
+#elif defined(CONFIG_FLASH_HAS_EXPLICIT_ERASE)
+    return true;
+#else
+    return false;
+#endif
+}
+#endif
+
 #ifdef __cplusplus
 }
 #endif

boot/zephyr/include/mcuboot_config/mcuboot_config.h

@@ -280,6 +280,29 @@
 #define MCUBOOT_ERASE_PROGRESSIVELY
 #endif
 
+/*
+ * Devices that do not require erase prior to write or do not support
+ * erase should avoid emulation of erase by additional write.
+ * The emulation is also taking time which doubles required write time
+ * for such devices.
+ */
+#ifdef CONFIG_MCUBOOT_STORAGE_WITHOUT_ERASE
+#define MCUBOOT_SUPPORT_DEV_WITHOUT_ERASE
+#endif
+
+#ifdef CONFIG_MCUBOOT_STORAGE_WITH_ERASE
+#define MCUBOOT_SUPPORT_DEV_WITH_ERASE
+#endif
+
+/*
+ * MCUboot often calls erase on device just to remove data or make application
+ * image not recognizable. In such instances it may be faster to just remove
+ * portion of data to make image unrecognizable.
+ */
+#ifdef CONFIG_MCUBOOT_STORAGE_MINIMAL_SCRAMBLE
+#define MCUBOOT_MINIMAL_SCRAMBLE
+#endif
+
 /*
  * Enabling this option uses newer flash map APIs. This saves RAM and
  * avoids deprecated API usage.