doc: move README.falcon to HTML

Move the Falcon mode documentation to HTML.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>

2 files changed, 259 insertions, 0 deletions

diff --git a/doc/develop/falcon.rst b/doc/develop/falcon.rst
new file mode 100644
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+.. SPDX-License-Identifier: GPL-2.0-or-later
+
+Falcon Mode
+===========
+
+Introduction
+------------
+
+This document provides an overview of how to add support for Falcon Mode
+to a board.
+
+Falcon Mode is introduced to speed up the booting process, allowing
+to boot a Linux kernel (or whatever image) without a full blown U-Boot.
+
+Falcon Mode relies on the SPL framework. In fact, to make booting faster,
+U-Boot is split into two parts: the SPL (Secondary Program Loader) and U-Boot
+image. In most implementations, SPL is used to start U-Boot when booting from
+a mass storage, such as NAND or SD-Card. SPL has now support for other media,
+and can generally be seen as a way to start an image performing the minimum
+required initialization. SPL mainly initializes the RAM controller, and then
+copies U-Boot image into the memory.
+
+The Falcon Mode extends this way allowing to start the Linux kernel directly
+from SPL. A new command is added to U-Boot to prepare the parameters that SPL
+must pass to the kernel, using ATAGS or Device Tree.
+
+In normal mode, these parameters are generated each time before
+loading the kernel, passing to Linux the address in memory where
+the parameters can be read.
+With Falcon Mode, this snapshot can be saved into persistent storage and SPL is
+informed to load it before running the kernel.
+
+To boot the kernel, these steps under a Falcon-aware U-Boot are required:
+
+1. Boot the board into U-Boot.
+    After loading the desired legacy-format kernel image into memory (and DT as
+    well, if used), use the "spl export" command to generate the kernel
+    parameters area or the DT.  U-Boot runs as when it boots the kernel, but
+    stops before passing the control to the kernel.
+
+2. Save the prepared snapshot into persistent media.
+    The address where to save it must be configured into board configuration
+    file (CONFIG_CMD_SPL_NAND_OFS for NAND).
+
+3. Boot the board into Falcon Mode. SPL will load the kernel and copy
+    the parameters which are saved in the persistent area to the required
+    address. If a valid uImage is not found at the defined location, U-Boot
+    will be booted instead.
+
+It is required to implement a custom mechanism to select if SPL loads U-Boot
+or another image.
+
+The value of a GPIO is a simple way to operate the selection, as well as
+reading a character from the SPL console if CONFIG_SPL_CONSOLE is set.
+
+Falcon Mode is generally activated by setting CONFIG_SPL_OS_BOOT. This tells
+SPL that U-Boot is not the only available image that SPL is able to start.
+
+Configuration
+-------------
+
+CONFIG_CMD_SPL
+    Enable the "spl export" command.
+    The command "spl export" is then available in U-Boot mode.
+
+CONFIG_SYS_SPL_ARGS_ADDR
+    Address in RAM where the parameters must be copied by SPL.
+    In most cases, it is <start_of_ram> + 0x100.
+
+CONFIG_SYS_NAND_SPL_KERNEL_OFFS
+    Offset in NAND where the kernel is stored
+
+CONFIG_CMD_SPL_NAND_OFS
+    Offset in NAND where the parameters area was saved.
+
+CONFIG_CMD_SPL_NOR_OFS
+    Offset in NOR where the parameters area was saved.
+
+CONFIG_CMD_SPL_WRITE_SIZE
+    Size of the parameters area to be copied
+
+CONFIG_SPL_OS_BOOT
+    Activate Falcon Mode.
+
+Function that a board must implement
+------------------------------------
+
+void spl_board_prepare_for_linux(void)
+    optional, called from SPL before starting the kernel
+
+spl_start_uboot()
+    required, returns "0" if SPL should start the kernel, "1" if U-Boot
+    must be started.
+
+Environment variables
+---------------------
+
+A board may chose to look at the environment for decisions about falcon
+mode.  In this case the following variables may be supported:
+
+boot_os
+    Set to yes/Yes/true/True/1 to enable booting to OS,
+    any other value to fall back to U-Boot (including unset)
+
+falcon_args_file
+    Filename to load as the 'args' portion of falcon mode rather than the
+    hard-coded value.
+
+falcon_image_file
+    Filename to load as the OS image portion of falcon mode rather than the
+    hard-coded value.
+
+Using spl command
+-----------------
+
+spl - SPL configuration
+
+Usage::
+
+    spl export <img=atags|fdt> [kernel_addr] [initrd_addr] [fdt_addr ]
+
+img
+    "atags" or "fdt"
+
+kernel_addr
+    kernel is loaded as part of the boot process, but it is not started.
+    This is the address where a kernel image is stored.
+
+initrd_addr
+    Address of initial ramdisk
+    can be set to "-" if fdt_addr without initrd_addr is used
+
+fdt_addr
+    in case of fdt, the address of the device tree.
+
+The *spl export* command does not write to a storage media. The user is
+responsible to transfer the gathered information (assembled ATAGS list
+or prepared FDT) from temporary storage in RAM into persistent storage
+after each run of *spl export*. Unfortunately the position of temporary
+storage can not be predicted nor provided at command line, it depends
+highly on your system setup and your provided data (ATAGS or FDT).
+However at the end of an successful *spl export* run it will print the
+RAM address of temporary storage. The RAM address of FDT will also be
+set in the environment variable *fdtargsaddr*, the new length of the
+prepared FDT will be set in the environment variable *fdtargslen*.
+These environment variables can be used in scripts for writing updated
+FDT to persistent storage.
+
+Now the user have to save the generated BLOB from that printed address
+to the pre-defined address in persistent storage
+(CONFIG_CMD_SPL_NAND_OFS in case of NAND).
+The following example shows how to prepare the data for Falcon Mode on
+twister board with ATAGS BLOB.
+
+The *spl export* command is prepared to work with ATAGS and FDT. However,
+using FDT is at the moment untested. The ppc port (see a3m071 example
+later) prepares the fdt blob with the fdt command instead.
+
+
+Usage on the twister board
+--------------------------
+
+Using mtd names with the following (default) configuration
+for mtdparts::
+
+    device nand0 <omap2-nand.0>, # parts = 9
+     #: name        size        offset      mask_flags
+     0: MLO                 0x00080000      0x00000000      0
+     1: u-boot              0x00100000      0x00080000      0
+     2: env1                0x00040000      0x00180000      0
+     3: env2                0x00040000      0x001c0000      0
+     4: kernel              0x00600000      0x00200000      0
+     5: bootparms           0x00040000      0x00800000      0
+     6: splashimg           0x00200000      0x00840000      0
+     7: mini                0x02800000      0x00a40000      0
+     8: rootfs              0x1cdc0000      0x03240000      0
+
+::
+
+    twister => nand read 82000000 kernel
+
+    NAND read: device 0 offset 0x200000, size 0x600000
+    6291456 bytes read: OK
+
+Now the kernel is in RAM at address 0x82000000::
+
+    twister => spl export atags 0x82000000
+    ## Booting kernel from Legacy Image at 82000000 ...
+       Image Name:   Linux-3.5.0-rc4-14089-gda0b7f4
+       Image Type:   ARM Linux Kernel Image (uncompressed)
+       Data Size:    3654808 Bytes = 3.5 MiB
+       Load Address: 80008000
+       Entry Point:  80008000
+       Verifying Checksum ... OK
+       Loading Kernel Image ... OK
+    OK
+    cmdline subcommand not supported
+    bdt subcommand not supported
+    Argument image is now in RAM at: 0x80000100
+
+The result can be checked at address 0x80000100::
+
+    twister => md 0x80000100
+    80000100: 00000005 54410001 00000000 00000000    ......AT........
+    80000110: 00000000 00000067 54410009 746f6f72    ....g.....ATroot
+    80000120: 65642f3d 666e2f76 77722073 73666e20    =/dev/nfs rw nfs
+
+The parameters generated with this step can be saved into NAND at the offset
+0x800000 (value for twister for CONFIG_CMD_SPL_NAND_OFS)::
+
+    nand erase.part bootparms
+    nand write 0x80000100 bootparms 0x4000
+
+Now the parameters are stored into the NAND flash at the address
+CONFIG_CMD_SPL_NAND_OFS (=0x800000).
+
+Next time, the board can be started into Falcon Mode moving the
+setting the GPIO (on twister GPIO 55 is used) to kernel mode.
+
+The kernel is loaded directly by the SPL without passing through U-Boot.
+
+Example with FDT: a3m071 board
+-------------------------------
+
+To boot the Linux kernel from the SPL, the DT blob (fdt) needs to get
+prepared/patched first. U-Boot usually inserts some dynamic values into
+the DT binary (blob), e.g. autodetected memory size, MAC addresses,
+clocks speeds etc. To generate this patched DT blob, you can use
+the following command:
+
+1. Load fdt blob to SDRAM::
+
+        => tftp 1800000 a3m071/a3m071.dtb
+
+2. Set bootargs as desired for Linux booting (e.g. flash_mtd)::
+
+        => run mtdargs addip2 addtty
+
+3. Use "fdt" commands to patch the DT blob::
+
+        => fdt addr 1800000
+        => fdt boardsetup
+        => fdt chosen
+
+4. Display patched DT blob (optional)::
+
+        => fdt print
+
+5. Save fdt to NOR flash::
+
+        => erase fc060000 fc07ffff
+        => cp.b 1800000 fc060000 10000
+        ...
+
+
+Falcon Mode was presented at the RMLL 2012. Slides are available at:
+
+http://schedule2012.rmll.info/IMG/pdf/LSM2012_UbootFalconMode_Babic.pdf
diff --git a/doc/develop/index.rst b/doc/develop/index.rst
index ddbf8dad4a..263d404b4c 100644
--- a/doc/develop/index.rst
+++ b/doc/develop/index.rst
@@ -45,6 +45,7 @@ Implementation
    printf
    smbios
    spl
+   falcon
    uefi/index
    vbe
    version