On Tue, Feb 12, 2013 at 6:38 AM, Stefano Babic <sba...@denx.de> wrote: > Simple howto to add support to a board > for booting the kernel from SPL ("Falcon" mode). > > Signed-off-by: Stefano Babic <sba...@denx.de> > --- > Changes in v5: > - several fixes for the language, rephrasing some unclear parts (Vikram > Narayanan) > > Changes in v4: > - fix capitalization, styling, in spl help (Andreas Biessmann) > - move CONFIG_SPL_OS_BOOT before function in doc (Andreas Biessmann) > > Changes in v3: > - parameter initrd_addr was removed in V2 (Andreas Biessmann) > - added patch to fix help usage for spl export (Andreas Biessmann) > - Added empty lines (Otavio Salvador) > - add a more exhaustive description explaining that > spl export does not save into media (Lukasz Majewski). > > Changes in v2: > - spelling, language fixes (Andreas Biessman) > - rewrite some unclear sentences > - drop CONFIG_SPL_OS_BOOT_KEY > - make example with twister more exhaustive > > doc/README.falcon | 169 > +++++++++++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 169 insertions(+) > create mode 100644 doc/README.falcon > > diff --git a/doc/README.falcon b/doc/README.falcon > new file mode 100644 > index 0000000..72fe04a > --- /dev/null > +++ b/doc/README.falcon > @@ -0,0 +1,169 @@ > +U-Boot 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.
Add a newline after board or move Falcon Mode to same phrase. > +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. New line. > 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 usual U-Boot systems, these parameters are generated each time before "In usual U-Boot systems" Together with previous phrase and might be clear as: "In normal mode, these ..." > +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. > +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 area to the required > address. > + > +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_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 starts the kernel, "1" if U-Boot > + must be started. > + > + > +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 img is used > +fdt_addr : in case of fdt, the address of the device tree. > + > +The spl puts its result at a self gained position. The position is defined > at compile > +time or when generating the uImage but not at command line for 'spl export' > +(see spl_export(): gd->bd->bi_boot_params vs. images.ft_addr). > + > +spl export' does not write directly to a storage media. This command is > intended to save > +the prepared information in RAM. > +The user is responsible to save the data into the required media, as > described > +on the following example, at the offset set at compile time > +(CONFIG_CMD_SPL_NAND_OFS in case of NAND). > + > +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. > + > +Falcon Mode was presented at the RMLL 2012. Slides are available at: > + > +http://schedule2012.rmll.info/IMG/pdf/LSM2012_UbootFalconMode_Babic.pdf > -- > 1.7.9.5 > -- Otavio Salvador O.S. Systems E-mail: ota...@ossystems.com.br http://www.ossystems.com.br Mobile: +55 53 9981-7854 http://projetos.ossystems.com.br _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot