This is a preliminary documentation introducing different boot sequences, and notably the recovery mode.

Signed-off-by: Neil Armstrong narmstrong@baylibre.com Reviewed-by: Mattijs Korpershoek mkorpershoek@baylibre.com Reviewed-by: Simon Glass sjg@chromium.org --- Changes since v1: - Christian Hewitt did an overall grammar correction of the text, meaning of the text hasn't changed, thus I kept the Reviewed-by tags

doc/board/amlogic/boot-flow.rst | 134 ++++++++++++++++++++++++++++++++ doc/board/amlogic/index.rst | 1 + 2 files changed, 135 insertions(+) create mode 100644 doc/board/amlogic/boot-flow.rst

diff --git a/doc/board/amlogic/boot-flow.rst b/doc/board/amlogic/boot-flow.rst new file mode 100644 index 0000000000..1ca81f3c89 --- /dev/null +++ b/doc/board/amlogic/boot-flow.rst @@ -0,0 +1,134 @@ +.. SPDX-License-Identifier: GPL-2.0+ + +Amlogic SoC Boot Flow +===================== + +The Amlogic SoCs have a pre-defined boot sequence in the SoC ROM code. Here are +the possible boot sources of different SoC families supported by U-Boot: + +GX* & AXG family +---------------- + ++----------+--------------------+-------+-------+---------------+---------------+ +| | 1 | 2 | 3 | 4 | 5 | ++==========+====================+=======+=======+===============+===============+ +| S905 | POC=0: SPI NOR | eMMC | NAND | SD Card | USB Device | +| S905X | | | | | | +| S905L | | | | | | +| S905W | | | | | | +| S912 | | | | | | ++----------+--------------------+-------+-------+---------------+---------------+ +| S805X | POC=0: SPI NOR | eMMC | NAND | USB Device | - | +| A113D | | | | | | +| A113X | | | | | | ++----------+--------------------+-------+-------+---------------+---------------+ + +POC pin: `NAND_CLE` + +Some boards provide a button to force USB BOOT which disables the eMMC clock signal +to bypass the eMMC stage. Others have removable eMMC modules; removing the eMMC and +SDCard will allow boot from USB. + +An exception is the lafrite board (aml-s805x-xx) which has no SDCard slot and boots +from SPI. The only ways to boot the lafrite board from USB are: + + - Erase the first sectors of SPI NOR flash + - Insert an HDMI boot plug forcing boot over USB + +The VIM1 and initial VIM2 boards provide a test point on the eMMC signals to block +the storage from answering and continue to the next boot step. + +The USB Device boot uses the first USB interface. On some boards this port is only +available on an USB-A type connector and needs an special Type-A to Type-A cable to +communicate with the BootROM. + +G12* & SM1 family +----------------- + ++-------+-------+-------+---------------+---------------+---------------+---------------+ +| POC0 | POC1 | POC2 | 1 | 2 | 3 | 4 | ++=======+=======+=======+===============+===============+===============+===============+ +| 0 | 0 | 0 | USB Device | SPI NOR | NAND/eMMC | SDCard | ++-------+-------+-------+---------------+---------------+---------------+---------------+ +| 0 | 0 | 1 | USB Device | NAND/eMMC | SDCard | - | ++-------+-------+-------+---------------+---------------+---------------+---------------+ +| 0 | 1 | 0 | SPI NOR | NAND/eMMC | SDCard | USB Device | ++-------+-------+-------+---------------+---------------+---------------+---------------+ +| 0 | 1 | 1 | SPI NAND | NAND/eMMC | USB Device | - | ++-------+-------+-------+---------------+---------------+---------------+---------------+ +| 1 | 0 | 0 | USB Device | SPI NOR | NAND/eMMC | SDCard | ++-------+-------+-------+---------------+---------------+---------------+---------------+ +| 1 | 0 | 1 | USB Device | NAND/eMMC | SDCard | - | ++-------+-------+-------+---------------+---------------+---------------+---------------+ +| 1 | 1 | 0 | SPI NOR | NAND/eMMC | SDCard | USB Device | ++-------+-------+-------+---------------+---------------+---------------+---------------+ +| 1 | 1 | 1 | NAND/eMMC | SDCard | USB Device | - | ++-------+-------+-------+---------------+---------------+---------------+---------------+ + +The last option (1/1/1) is the normal default seen on production devices. + + * POC0 pin: `BOOT_4` (0 and all other 1 means SPI NAND boot first) + * POC1 pin: `BOOT_5` (0 and all other 1 means USB Device boot first + * POC2 pin: `BOOT_6` (0 and all other 1 means SPI NOR boot first) + +Most boards provide a button to force USB BOOT which lowers `BOOT_5` to 0. Some boards +provide a test point on the eMMC or SPI NOR clock signals to block the storage from +answering and continue to the next boot step. + +The Khadas VIM3/3L boards embed a microcontroller which sets POC signals according +to its configuration or a specific key press sequence to either boot from SPI NOR +or eMMC then SDCard, or boot as an USB Device. + +The Odroid N2/N2+ has a hardware switch to select between SPI NOR or eMMC boot. + +Boot Modes +---------- + + * SDCard + +The BootROM fetches the first SDCard sectors in one sequence, then checks the content +of the data. The BootROM expects to find the FIP binary in sector 1, 512 bytes offset +from the start. + + * eMMC + +The BootROM fetches the first sectors in one sequence, first on the main partition, +and then on the Boot0 followed by Boot1 HW partitions. After each read, the BootROM +checks the data and looks to the next partition if it fails. The BootROM expects to +find the FIP binary in sector 1, 512 bytes offset from the start. + + * SPI NOR + +The BootROM fetches the first SPI NOR sectors in one sequence, then checks the content +of the data. The BootROM expects to find the FIP binary in sector 1, 512 bytes offset +from the start. + + * NAND & SPI NAND + +These modes are rarely used in open platforms and no details are available. + + * USB Device + +The BootROM sets the USB Gadget interface to serve a custom USB protocol with the +USB ID 1b8e:c003. The Amlogic `update` utility is designed to use this protocol. It +is also implemented in the Amlogic Vendor U-Boot. + +The open-source `pyamlboot` utility https://github.com/superna9999/pyamlboot also +implements this protocol and can load U-Boot in memory in order to start the SoC +without any attached storage or to recover from a failed/incorrect image flash. + +HDMI Recovery +------------- + +The BootROM also briefly reads 8 bytes at address I2C 0x52 offset 0xf8 (248) on the +HDMI DDC bus. If the content is `boot@USB` it will force USB boot mode. If the content +is `boot@SDC` it will force SDCard boot mode. + +If USB Device doesn't enumerate or SD Card boot step doesn't work, the BootROM will +continue with the normal boot sequence. + +Special boot dongles can be built by connecting a 256bytes EEPROM set to answer on +address 0x52, and program `boot@USB` or `boot@SDC` at offset 0xf8 (248). + +Note: If the SoC is booted with USB Device forced at first step, it will keep the boot +order on warm reboot. Only cold reboot (power removed) will reset the boot order. diff --git a/doc/board/amlogic/index.rst b/doc/board/amlogic/index.rst index 9c7fadf2c0..8b9f1e2e1d 100644 --- a/doc/board/amlogic/index.rst +++ b/doc/board/amlogic/index.rst @@ -81,6 +81,7 @@ Boot Documentation :maxdepth: 1

pre-generated-fip + boot-flow

Board Documentation -------------------