env: am57xx: Implement A/B boot process

Add support for A/B boot process on AM57xx based boards:

  1. Define 'slot_suffix' variable (using 'ab_select' command)
  2. Extend 'emmc_android_boot' boot command (add commands for A/B boot
     process)

'ab_select' command is used to decide which slot should be used for
booting up. A/B metadata resides in 'misc' partition.

To activate the A/B boot process, the following config options must be
set:

    CONFIG_ANDROID_AB=y
    CONFIG_CMD_AB_SELECT=y

For successful A/B boot, the corresponding A/B infrastructure must be
involved on Android side [1] (including mounting system as root), and
disk must be partitioned accordingly.

When A/B boot is enabled, there are some known limitations currently
exist (not related to A/B patches, need to be implemented later):

  1. The 'Verified Boot' sequence is not supported
  2. dev path to system partition (system_a or system_b) is passed via
     'bootargs' as 'root=' argument like 'root=/dev/mmcblk1p12', but
     further we'll need to rework it with respect to dm-verity
     requirements [2]

In case when A/B partitions are not present in system (and A/B boot is
enabled), boot up process will be terminated and next message will be
shown:

    "boot_a(b) partition not found"

[1] https://source.android.com/devices/tech/ota/ab
[2] https://source.android.com/devices/tech/ota/ab/ab_implement#kernel

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

include/environment/ti/boot.h

@@ -23,6 +23,18 @@
 #define VBMETA_PART			""
 #endif
 
+#if defined(CONFIG_CMD_AB_SELECT)
+#define COMMON_PARTS \
+	"name=boot_a,size=20M,uuid=${uuid_gpt_boot_a};" \
+	"name=boot_b,size=20M,uuid=${uuid_gpt_boot_b};" \
+	"name=system_a,size=1024M,uuid=${uuid_gpt_system_a};" \
+	"name=system_b,size=1024M,uuid=${uuid_gpt_system_b};"
+#else
+#define COMMON_PARTS \
+	"name=boot,size=20M,uuid=${uuid_gpt_boot};" \
+	"name=system,size=1024M,uuid=${uuid_gpt_system};"
+#endif
+
 #ifndef PARTS_DEFAULT
 /* Define the default GPT table for eMMC */
 #define PARTS_DEFAULT \
@@ -38,8 +50,7 @@
 	"name=uboot-env,start=2432K,size=256K,uuid=${uuid_gpt_reserved};" \
 	"name=misc,size=128K,uuid=${uuid_gpt_misc};" \
 	"name=recovery,size=40M,uuid=${uuid_gpt_recovery};" \
-	"name=boot,size=10M,uuid=${uuid_gpt_boot};" \
-	"name=system,size=1024M,uuid=${uuid_gpt_system};" \
+	COMMON_PARTS \
 	"name=vendor,size=256M,uuid=${uuid_gpt_vendor};" \
 	VBMETA_PART \
 	"name=userdata,size=-,uuid=${uuid_gpt_userdata}"
@@ -58,6 +69,35 @@
 #define AVB_VERIFY_CMD ""
 #endif
 
+#define CONTROL_PARTITION "misc"
+
+#if defined(CONFIG_CMD_AB_SELECT)
+#define AB_SELECT \
+	"if part number mmc 1 " CONTROL_PARTITION " control_part_number; " \
+	"then " \
+		"echo " CONTROL_PARTITION \
+			" partition number:${control_part_number};" \
+		"ab_select slot_name mmc ${mmcdev}:${control_part_number};" \
+	"else " \
+		"echo " CONTROL_PARTITION " partition not found;" \
+		"exit;" \
+	"fi;" \
+	"setenv slot_suffix _${slot_name};" \
+	"if part number mmc ${mmcdev} system${slot_suffix} " \
+	"system_part_number; then " \
+		"setenv bootargs_ab " \
+		"ro root=/dev/mmcblk${mmcdev}p${system_part_number} " \
+		"rootwait init=/init skip_initramfs " \
+		"androidboot.slot_suffix=${slot_suffix};" \
+		"echo A/B cmdline addition: ${bootargs_ab};" \
+		"setenv bootargs ${bootargs} ${bootargs_ab};" \
+	"else " \
+		"echo system${slot_suffix} partition not found;" \
+	"fi;"
+#else
+#define AB_SELECT ""
+#endif
+
 #define DEFAULT_COMMON_BOOT_TI_ARGS \
 	"console=" CONSOLEDEV ",115200n8\0" \
 	"fdtfile=undefined\0" \
@@ -86,10 +126,16 @@
 		"mmc dev $mmcdev; " \
 		"mmc rescan; " \
 		AVB_VERIFY_CHECK \
-		"part start mmc ${mmcdev} boot boot_start; " \
-		"part size mmc ${mmcdev} boot boot_size; " \
+		AB_SELECT \
+		"if part start mmc ${mmcdev} boot${slot_suffix} boot_start; " \
+		"then " \
+			"part size mmc ${mmcdev} boot${slot_suffix} " \
+				"boot_size; " \
 			"mmc read ${loadaddr} ${boot_start} ${boot_size}; " \
-		"bootm ${loadaddr}#${fdtfile};\0 "
+			"bootm ${loadaddr}#${fdtfile}; " \
+		"else " \
+			"echo boot${slot_suffix} partition not found; " \
+		"fi;\0"
 
 #ifdef CONFIG_OMAP54XX