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doc: imx: psb: Document usage of SRC_GPR10 PERSIST_SECONDARY_BOOT for A/B switching

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Document SRC_GPR10 PERSIST_SECONDARY_BOOT functionality. This is useful for
reliable bootloader A/B updates, as it permits switching between two copies
of bootloader at different offsets of the same storage. The switch happens
in case one copy is corrupted OR can be enforced by user. This functionality
is present at least since i.MX53, however is poorly documented in all known
SoC datasheets, hence this document aims to clarify the usage, currently on
i.MX7D and i.MX8MM.

Signed-off-by: Marek Vasut <marex@denx.de> # Original MX7D work, this document
Signed-off-by: Igor Opaniuk <igor.opaniuk@foundries.io> # All the MX8M work
Cc: Christoph Niedermaier <cniedermaier@dh-electronics.de>
Cc: Fabio Estevam <festevam@gmail.com>
Cc: Harald Seiler <hws@denx.de>
Cc: Igor Opaniuk <igor.opaniuk@foundries.io>
Cc: Jan Kiszka <jan.kiszka@siemens.com>
Cc: Ludwig Zenz <lzenz@dh-electronics.com>
Cc: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Cc: Peng Fan <peng.fan@nxp.com>
Cc: Stefano Babic <sbabic@denx.de>
Cc: Ye Li <ye.li@nxp.com>
Cc: uboot-imx <uboot-imx@nxp.com>
Reviewed-by: Peng Fan <peng.fan@nxp.com>
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Marek Vasut 2021-03-25 01:20:48 +01:00 committed by Stefano Babic
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.. SPDX-License-Identifier: GPL-2.0+
NXP i.MX Machine-specific doc
=============================
.. toctree::
:maxdepth: 2
misc/index

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.. SPDX-License-Identifier: GPL-2.0+
Miscellaneous
=============
.. toctree::
:maxdepth: 2
psb

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i.MX7D/i.MX8MM SRC_GPR10 PERSIST_SECONDARY_BOOT for bootloader A/B switching
============================================================================
Introduction
------------
Since at least iMX53 until iMX8MM, it is possible to have two copies of
bootloader in SD/eMMC and switch between them. The switch is triggered
either by the BootROM in case the bootloader image is faulty OR can be
enforced by the user.
Operation
---------
#. Upon Power-On Reset (POR)
- SRC_GPR10 bit PERSIST_SECONDARY_BOOT is set to 0
- BootROM attempts to start bootloader A-copy
- if A-copy valid
- BootROM starts A-copy
- END
- if A-copy NOT valid
- BootROM sets SRC_GPR10 bit PERSIST_SECONDARY_BOOT to 1
- BootROM triggers WARM reset, GOTO 1)
- END
#. Upon COLD Reset
- GOTO 1)
- END
#. Upon WARM Reset
- SRC_GPR10 bit PERSIST_SECONDARY_BOOT is retained
- if SRC_GPR10 bit PERSIST_SECONDARY_BOOT is 0
- BootROM attempts to start bootloader A-copy
- if A-copy valid
- BootROM starts A-copy
- END
- if A-copy NOT valid
- BootROM sets SRC_GPR10 bit PERSIST_SECONDARY_BOOT to 1
- BootROM triggers WARM reset. GOTO 1.3)
- END
- if SRC_GPR10 bit PERSIST_SECONDARY_BOOT is 1
- BootROM attempts to start bootloader B-copy
- if B-copy valid
- BootROM starts B-copy
- END
- if B-copy NOT valid
- System hangs
- END
Setup
-----
The bootloader A-copy must be placed at predetermined offset in SD/eMMC. The
bootloader B-copy area offset is determined by an offset stored in Secondary
Image Table (SIT). The SIT must be placed at predetermined offset in SD/eMMC.
The following table contains offset of SIT, bootloader A-copy and recommended
bootloader B-copy offset. The offsets are in 512 Byte sector units (that is
offset 0x1 means 512 Bytes from the start of SD/eMMC card data partition).
For details on the addition of two numbers in recommended B-copy offset, see
SIT format below.
+----------+--------------------+-----------------------+-----------------------------+
| SoC | SIT offset (fixed) | A-copy offset (fixed) | B-copy offset (recommended) |
+----------+--------------------+-----------------------+-----------------------------+
| iMX7D | 0x1 | 0x2 | 0x800+0x2 |
+----------+--------------------+-----------------------+-----------------------------+
| iMX8MM | 0x41 | 0x42 | 0x1000+0x42 |
+----------+--------------------+-----------------------+-----------------------------+
SIT format
~~~~~~~~~~
SIT is a 20 byte long structure containing of 5 32-bit words. Those encode
bootloader B-copy area offset (called "firstSectorNumber"), magic value
(called "tag") that is always 0x00112233, and three unused words set to 0.
SIT is documented in [1] and [2]. Example SIT are below::
$ hexdump -vC sit-mx7d.bin
00000000 00 00 00 00
00000004 00 00 00 00
00000008 33 22 11 00 <--- This is the "tag"
0000000c 00 08 00 00 <--- This is the "firstSectorNumber"
00000010 00 00 00 00
$ hexdump -vC sit-mx8mm.bin
00000000 00 00 00 00
00000004 00 00 00 00
00000008 33 22 11 00 <--- This is the "tag"
0000000c 00 10 00 00 <--- This is the "firstSectorNumber"
00000010 00 00 00 00
B-copy area offset ("firstSectorNumber") is offset, in units of 512 Byte
sectors, that is added to the start of boot media when switching between
A-copy and B-copy. For A-copy, this offset is 0x0. For B-copy, this offset
is determined by SIT (e.g. if firstSectorNumber is 0x1000 as it is above
in sit-mx8mm.bin, then the B-copy offset is 0x1000 sectors = 2 MiB).
Bootloader A-copy (e.g. u-boot.imx or flash.bin) is placed at fixed offset
from A-copy area offset (e.g. 0x2 sectors from sector 0x0 for iMX7D, which
means u-boot.imx A-copy must be written to sector 0x2).
The same applies to bootloader B-copy, which is placed at fixed offset from
B-copy area offset determined by SIT (e.g. 0x2 sectors from sector 0x800 [see
sit-mx7d.bin example above, this can be changed in SIT firstSectorNumber] for
iMX7D, which means u-boot.imx B-copy must be written to sector 0x802)
**WARNING:**
B-copy area offset ("firstSectorNumber") is NOT equal to bootloader
(image, which is u-boot.imx or flash.bin) B-copy offset.
To generate SIT, use for example the following bourne shell printf command::
$ printf '\x0\x0\x0\x0\x0\x0\x0\x0\x33\x22\x11\x00\x00\x08\x00\x00\x0\x0\x0\x0' > sit-mx7d.bin
$ printf '\x0\x0\x0\x0\x0\x0\x0\x0\x33\x22\x11\x00\x00\x10\x00\x00\x0\x0\x0\x0' > sit-mx8mm.bin
Write bootloader A/B copy and SIT to SD/eMMC
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Examples of writing SIT and two copies of bootloader to SD or eMMC:
- iMX8MM, SD card at /dev/sdX, Linux command line
::
$ dd if=sit-mx8mm.bin of=/dev/sdX bs=512 seek=65
$ dd if=flash.bin of=/dev/sdX bs=512 seek=66
$ dd if=flash.bin of=/dev/sdX bs=512 seek=4162
- iMX8MM, eMMC 1 data partition, U-Boot command line
::
=> mmc partconf 1 0 0 0
=> dhcp ${loadaddr} sit-mx8mm.bin
=> mmc dev 1
=> mmc write ${loadaddr} 0x41 0x1
=> dhcp ${loadaddr} flash.bin
=> setexpr blkcnt ${filesize} + 0x1ff && setexpr blkcnt
=> mmc dev 1
=> mmc write ${loadaddr} 0x42 ${blkcnt}
=> mmc write ${loadaddr} 0x1042 ${blkcnt}
WARM reset into B-copy using WDT
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
To perform a reboot into B-copy, the PERSIST_SECONDARY_BOOT must be set
in SRC_GPR0 register. Example on iMX8MM::
=> mw 0x30390098 0x40000000
A WARM reset can be triggered using WDT as follows::
=> mw.w 0x30280000 0x25
References
----------
.. [1] i.MX 7Dual Applications Processor Reference Manual, Rev. 1, 01/2018 ; section 6.6.5.3.5 Redundant boot support for expansion device
.. [2] i.MX 8M Mini Applications Processor Reference Manual, Rev. 3, 11/2020 ; section 6.1.5.4.5 Redundant boot support for expansion device

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arch/index
Machine-specific doc
--------------------
These books provide programming details about machine-specific
implementation.
.. toctree::
:maxdepth: 2
imx/index
Board-specific doc
------------------