cmd: Add 'ab_select' command

For A/B system update support the Android boot process requires to send
'androidboot.slot_suffix' parameter as a command line argument. This
patch implementes 'ab_select' command which allows us to obtain current
slot by processing the A/B metadata.

The patch was extracted from commit [1] with one modification: the
separator for specifying the name of metadata partition was changed
from ';' to '#', because ';' is used for commands separation.

[1] https://android-review.googlesource.com/c/platform/external/u-boot/+/729880/2

Signed-off-by: Ruslan Trofymenko <ruslan.trofymenko@linaro.org>
Signed-off-by: Igor Opaniuk <igor.opaniuk@gmail.com>
Reviewed-by: Alistair Strachan <astrachan@google.com>
Reviewed-by: Sam Protsenko <semen.protsenko@linaro.org>
Reviewed-by: Simon Glass <sjg@chromium.org>

cmd/Kconfig

@@ -1198,6 +1198,21 @@ config CMD_SETEXPR
 
 endmenu
 
+menu "Android support commands"
+
+config CMD_AB_SELECT
+	bool "ab_select"
+	default n
+	depends on ANDROID_AB
+	help
+	  On Android devices with more than one boot slot (multiple copies of
+	  the kernel and system images) this provides a command to select which
+	  slot should be used to boot from and register the boot attempt. This
+	  is used by the new A/B update model where one slot is updated in the
+	  background while running from the other slot.
+
+endmenu
+
 if NET
 
 menuconfig CMD_NET

cmd/Makefile

@@ -12,6 +12,7 @@ obj-y += version.o
 
 # command
 obj-$(CONFIG_CMD_AES) += aes.o
+obj-$(CONFIG_CMD_AB_SELECT) += ab_select.o
 obj-$(CONFIG_CMD_ADC) += adc.o
 obj-$(CONFIG_CMD_ARMFLASH) += armflash.o
 obj-y += blk_common.o

cmd/ab_select.c

@@ -0,0 +1,52 @@
+// SPDX-License-Identifier: BSD-2-Clause
+/*
+ * Copyright (C) 2017 The Android Open Source Project
+ */
+
+#include <android_ab.h>
+#include <command.h>
+
+static int do_ab_select(cmd_tbl_t *cmdtp, int flag, int argc,
+			char * const argv[])
+{
+	int ret;
+	struct blk_desc *dev_desc;
+	disk_partition_t part_info;
+	char slot[2];
+
+	if (argc != 4)
+		return CMD_RET_USAGE;
+
+	/* Lookup the "misc" partition from argv[2] and argv[3] */
+	if (part_get_info_by_dev_and_name_or_num(argv[2], argv[3],
+						 &dev_desc, &part_info) < 0) {
+		return CMD_RET_FAILURE;
+	}
+
+	ret = ab_select_slot(dev_desc, &part_info);
+	if (ret < 0) {
+		printf("Android boot failed, error %d.\n", ret);
+		return CMD_RET_FAILURE;
+	}
+
+	/* Android standard slot names are 'a', 'b', ... */
+	slot[0] = BOOT_SLOT_NAME(ret);
+	slot[1] = '\0';
+	env_set(argv[1], slot);
+	printf("ANDROID: Booting slot: %s\n", slot);
+	return CMD_RET_SUCCESS;
+}
+
+U_BOOT_CMD(ab_select, 4, 0, do_ab_select,
+	   "Select the slot used to boot from and register the boot attempt.",
+	   "<slot_var_name> <interface> <dev[:part|#part_name]>\n"
+	   "    - Load the slot metadata from the partition 'part' on\n"
+	   "      device type 'interface' instance 'dev' and store the active\n"
+	   "      slot in the 'slot_var_name' variable. This also updates the\n"
+	   "      Android slot metadata with a boot attempt, which can cause\n"
+	   "      successive calls to this function to return a different result\n"
+	   "      if the returned slot runs out of boot attempts.\n"
+	   "    - If 'part_name' is passed, preceded with a # instead of :, the\n"
+	   "      partition name whose label is 'part_name' will be looked up in\n"
+	   "      the partition table. This is commonly the \"misc\" partition.\n"
+);