[PATCH v3 1/1] doc: describe TPL/VPL/SPL boot
Paul Barker
paul.barker.ct at bp.renesas.com
Sat Aug 26 12:42:08 CEST 2023
On 26/08/2023 10:13, Heinrich Schuchardt wrote:
> This is a stub describing how TPL, VPL, and SPL load the next boot stages
> on a detail level for users.
>
> For sure we will need a few patches on top to catch the whole complexity.
>
> Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt at canonical.com>
> ---
> v3:
> Call TPL Tertiary Program Loader, VPL Verifying Program Loader
> Put Power PC flow into an info box to stick out
> Add link to Falcon Mode
> Fix typos
> v2:
> Mention that PowerPC uses a different naming convention.
> Group boot devices by type
> Correct reference to UBI
> Fix typos
> ---
> doc/usage/index.rst | 1 +
> doc/usage/spl_boot.rst | 323 +++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 324 insertions(+)
> create mode 100644 doc/usage/spl_boot.rst
>
> diff --git a/doc/usage/index.rst b/doc/usage/index.rst
> index 3326ec82ff..f45a7f5502 100644
> --- a/doc/usage/index.rst
> +++ b/doc/usage/index.rst
> @@ -4,6 +4,7 @@ Use U-Boot
> .. toctree::
> :maxdepth: 1
>
> + spl_boot
> blkmap
> dfu
> environment
> diff --git a/doc/usage/spl_boot.rst b/doc/usage/spl_boot.rst
> new file mode 100644
> index 0000000000..ad6bf0ab69
> --- /dev/null
> +++ b/doc/usage/spl_boot.rst
> @@ -0,0 +1,323 @@
> +.. SPDX-License-Identifier: GPL-2.0-or-later
> +
> +Booting from TPL/SPL
> +====================
> +
> +The main U-Boot binary may be too large to be loaded directly by the Boot ROM.
> +This was the original driver for splitting up U-Boot into multiple boot stages.
> +
> +U-Boot typically goes through the following boot phases where TPL, VPL, and SPL
> +are optional. While many boards use SPL only few use TPL.
> +
> +TPL
> + Tertiary Program Loader. Very early init, as tiny as possible. This loads SPL
> + (or VPL if enabled).
> +
> +VPL
> + Verifying Program Loader. Optional verification step, which can select one of
> + several SPL binaries, if A/B verified boot is enabled. Implementation of the
> + VPL logic is work-in-progress. For now it just boots into SPL.
> +
> +SPL
> + Secondary Program Loader. Sets up SDRAM and loads U-Boot proper. It may also
> + load other firmware components.
I'd fold the bullet points below (BL31, EDK II, Falcon mode & OpenSBI
loading) into this description to improve the flow of the document.
> +
> +U-Boot
> + U-Boot proper, containing the command line and the logic to load an
> + operating system, e.g. via UEFI.
Change after the first comma to "this is the only stage containing the
command line...", then the extra line below the following note saying
this can be dropped.
> +
> +.. note::
> +
> + The naming convention on the PowerPC architecture deviates from the other
> + archtitectures. Here the boot sequence is SPL->TPL->U-Boot.
> +
> +Only main U-Boot has a command line interface.
> +
> +Further usages for U-Boot SPL comprise:
> +
> +* launching BL31 of ARM Trusted Firmware which invokes U-Boot as BL33
> +* launching EDK II
> +* launching Linux, e.g. :doc:`Falcon Mode' <../develop/falcon>`
> +* launching RISC-V OpenSBI which invokes main U-Boot> +
> +Target binaries
> +---------------
> +
> +Binaries loaded by SPL/TPL can be:
> +
> +* raw binaries where the entry address equals the start address. This is the
> + only binary format supported by TPL.
> +* :doc:`FIT <fit/index>` images
> +* legacy U-Boot images
> +
> +Configuration
> +~~~~~~~~~~~~~
> +
> +Raw images are only supported in SPL if CONFIG_SPL_RAW_IMAGE_SUPPORT=y.
> +
> +CONFIG_SPL_FIT=y and CONFIG_SPL_LOAD_FIT=y are needed to load FIT images.
> +
> +CONFIG_SPL_LEGACY_IMAGE_FORMAT=y is needed to load legacy U-Boot images.
> +CONFIG_SPL_LEGACY_IMAGE_CRC_CHECK=y enables checking the CRC32 of legacy U-Boot
> +images.
> +
> +Image load methods
> +------------------
> +
> +The image boot methods available for a board must be defined in two places:
> +
> +The board code implements a function board_boot_order() enumerating up to
> +five boot methods and the sequence in which they are tried. (The maximum
> +number of boot methods is currently hard coded as variable spl_boot_list[]).
> +If there is only one boot method function, spl_boot_device() may be implemented
> +instead.
> +
> +The configuration controls which of these boot methods are actually available.
> +
> +Loading from block devices
> +~~~~~~~~~~~~~~~~~~~~~~~~~~
> +
> +MMC1, MMC2, MMC2_2
> + These methods read an image from SD card or eMMC. The first digit after
> + 'MMC' indicates the device number. Required configuration settings include:
> +
> + * CONFIG_SPL_MMC=y or CONFIG_TPL_MMC=y
> +
> + To use a PCI connected MMC controller you need to additionally specify:
> +
> + * CONFIG_SPL_PCI=y
> +
> + * CONFIG_SPL_PCI_PNP=y
> +
> + * CONFIG_MMC=y
> +
> + * CONFIG_MMC_PCI=y
> +
> + * CONFIG_MMC_SDHCI=y
> +
> + To load from a file system use:
> +
> + * CONFIG_SPL_FS_FAT=y or CONFIG_SPL_FS_EXT=y
> +
> + * CONFIG_SPL_FS_LOAD_PAYLOAD_NAME="<filepath>"
> +
> +NVMe
> + This methods load the image from an NVMe drive.
> + Required configuration settings include:
> +
> + * CONFIG_SPL_PCI=y
> +
> + * CONFIG_SPL_PCI_PNP=y
> +
> + * CONFIG_SPL_NVME=y
> +
> + * CONFIG_SPL_NVME_PCI=y
> +
> + * CONFIG_SPL_NVME_BOOT_DEVICE (number of the NVMe device)
> +
> + * CONFIG_SYS_NVME_BOOT_PARTITION (partition to read from)
> +
> + To load from a file system use:
> +
> + * CONFIG_SPL_FS_FAT=y or CONFIG_SPL_FS_EXT=y
> +
> + * CONFIG_SPL_FS_LOAD_PAYLOAD_NAME="<filepath>"
> +
> +SATA
> + This method reads an image from a SATA drive.
> + Required configuration settings include:
> +
> + * CONFIG_SPL_SATA=y or CONFIG_TPL_SATA=y
> +
> + To use a PCIe connecte SATA controller you additionally need:
> +
> + * CONFIG_SPL_PCI=y
> +
> + * CONFIG_SPL_SATA=y
> +
> + * CONFIG_SPL_AHCI_PCI=y
> +
> + * CONFIG_SPL_PCI_PNP=y
> +
> + To load from a file system use:
> +
> + * CONFIG_SPL_FS_FAT=y
> +
> + * CONFIG_SYS_SATA_FAT_BOOT_PARTITION=<partition number>
> +
> + * CONFIG_SPL_FS_LOAD_PAYLOAD_NAME="<filepath>"
> +
> +USB
> + The USB method loads an image from a USB block device.
> + Required configuration settings include:
> +
> + * CONFIG_SPL_USB_HOST=y
> +
> + * CONFIG_SPL_USB_STORAGE=y
> +
> + To use a PCI connected USB 3.0 controller you additionally need:
> +
> + * CONFIG_SPL_FS_FAT=y
> +
> + * CONFIG_SPL_PCI=y
> +
> + * CONFIG_SPL_PCI_PNP=y
> +
> + * CONFIG_USB=y
> +
> + * CONFIG_USB_XHCI_HCD=y
> +
> + * CONFIG_USB_XHCI_PCI=y
> +
> + To load from a file system use:
> +
> + * CONFIG_SPL_FS_FAT=y or CONFIG_SPL_FS_EXT=y
> +
> + * CONFIG_SYS_USB_FAT_BOOT_PARTITION=<partition number>
> +
> + * CONFIG_SPL_FS_LOAD_PAYLOAD_NAME="<filepath>"
> +
> +Loading from flash devices
> +~~~~~~~~~~~~~~~~~~~~~~~~~~
I'd say "raw flash devices" to make the distinction from flash block
devices (e.g. SSD/NVMe) clear.
> +
> +NAND
> + This method loads the image from NAND flash. To read from raw NAND the
> + following configuration settings are required:
> +
> + * CONFIG_SPL_NAND_SUPPORT=y or CONFIG_TPL_NAND_SUPPORT=y
> +
> + If CONFIG_SPL_NAND_RAW_ONLY=y only raw images can be loaded.
> +
> + For using UBI (Unsorted Block Images) volumes to read from NAND the
> + following configuration settings are required:
> +
> + * CONFIG_SPL_UBI=y or CONFIG_TPL_UBI=y
> +
> + The UBI volume to read can either be specified
> +
> + * by name using CONFIG_SPL_UBI_LOAD_BY_VOLNAME or
> +
> + * by number using CONFIG_SPL_UBI_LOAD_MONITOR_ID.
> +
> +NOR
> + This method loads the image from NOR flash.
> + Required configuration settings include:
> +
> + * CONFIG_SPL_NOR_SUPPORT=y or CONFIG_TPL_NOR_SUPPORT=y
> +
> +OneNAND
> + This methods loads the image from a OneNAND device. To read from raw OneNAND
> + the following configuration settings are required:
> +
> + * CONFIG_SPL_ONENAND_SUPPORT=y or CONFIG_TPL_ONENAND_SUPPORT=y
> +
> + For using the Ubi file system to read from NAND the following configuration
> + settings are required:
> +
> + * CONFIG_SPL_UBI=y or CONFIG_TPL_UBI=y
> +
> +SPI
> + This method loads an image form SPI NOR flash.
> + Required configuration settings include:
> +
> + * CONFIG_SPL_DM_SPI=y
> +
> + * CONFIG_SPL_SPI_FLASH=y
> +
> + * CONFIG_SPI_LOAD=y or CONFIG_TPL_SPI_LOAD=y
> +
> +
> +Sunxi SPI
> + This method which is specific to Allwinner SoCs loads an image form SPI NOR
> + flash. Required configuration settings include:
> +
> + * CONFIG_SPL_SPI_SUNXI=y
> +
> +Loading from other devices
> +~~~~~~~~~~~~~~~~~~~~~~~~~~
> +
> +BOOTROM
> + The binary is loaded by the boot ROM.
> + Required configuration settings include:
> +
> + * CONFIG_SPL_BOOTROM_SUPPORT=y or CONFIG_TPL_BOOTROM_SUPPORT=y
> +
> +DFU
> + :doc:`Device Firmware Upgrade <dfu>` is used to load the binary into RAM.
> + Required configuration settings include:
> +
> + * CONFIG_DFU=y
> +
> + * CONFIG_SPL_RAM_SUPPORT=y or CONFIG TPL_RAM_SUPPORT=y
> +
> +Ethernet
> + This method loads an image over Ethernet. The BOOTP protocol is used to find
> + a TFTP server and binary name. The binary is downloaded via the TFTP
> + protocol. Required configuration settings include:
> +
> + * CONFIG_SPL_NET=y or CONFIG_TPL_NET=y
> +
> + * CONFIG_SPL_ETH_DEVICE=y or CONFIG_DM_USB_GADGET=y
> +
> +FEL
> + This method does not actually load an image for U-Boot.
> + FEL is a routine contained in the boot ROM of Allwinner SoCs which serves
> + for the initial programming or recovery via USB
> +
> +RAM
> + This method uses an image preloaded into RAM.
> + Required configuration settings include:
> +
> + * CONFIG_SPL_RAM_SUPPORT=y or CONFIG_TPL_RAM_SUPPORT=y
> +
> + * CONFIG_RAM_DEVICE=y
> +
> +Sandbox file
> + On the sandbox this method loads an image from the host file system.
> +
> +Sandbox image
> + On the sandbox this method loads an image from the host file system.
> +
> +Semihosting
> + When running in an ARM or RISC-V virtual machine the semihosting method can
> + be used to load an image from the host file system.
> + Required configuration settings include:
> +
> + * CONFIG_SPL_SEMIHOSTING=y
> +
> + * CONFIG_SPL_SEMIHOSTING_FALLBACK=y
> +
> + * CONFIG_SPL_FS_LOAD_PAYLOAD_NAME=<path to file>
> +
> +UART
> + This method loads an image via the Y-Modem protocol from the UART.
> + Required configuration settings include:
> +
> + * CONFIG_SPL_YMODEM_SUPPORT=y or CONFIG_TPL_YMODEM_SUPPORT=y
> +
> +USB SDP
> + This method loads the image using the Serial Download Protocol as
> + implemented by the boot ROM of the i.MX family of SoCs.
> +
> + Required configuration settings include:
> +
> + * CONFIG_SPL_SERIAL=y
> +
> + * CONFIG_SPL_USB_SDP_SUPPORT=y or CONFIG_TPL_USB_SDP_SUPPORT
> +
> +VBE Simple
> + This method is used by the VPL stage to extract the next stage image from
> + the loaded image.
> +
> + Required configuration settings include:
> +
> + * CONFIG_VPL=y
> +
> + * CONFIG_SPL_BOOTMETH_VBE_SIMPLE_FW=y or CONFIG_TPL_BOOTMETH_VBE_SIMPLE_FW=y
> +
> +XIP
> + This method executes an image in place.
> +
> + Required configuration settings include:
> +
> + * CONFIG_SPL_XIP_SUPPORT
My comments above are minor style suggestions so whether or not they're
changed:
Reviewed-by: Paul Barker <paul.barker.ct at bp.renesas.com>
Thanks,
Paul
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