[U-Boot] [PATCH v2 1/2] Add README for the "Falcon" mode
Otavio Salvador
otavio at ossystems.com.br
Wed Nov 14 11:29:05 CET 2012
On Tue, Nov 13, 2012 at 9:11 AM, Stefano Babic <sbabic at denx.de> wrote:
> Simple howto to add support to a board
> for booting the kernel from SPL ("Falcon" mode).
>
> Signed-off-by: Stefano Babic <sbabic at denx.de>
> ---
> 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 | 163
> +++++++++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 163 insertions(+)
> create mode 100644 doc/README.falcon
>
> diff --git a/doc/README.falcon b/doc/README.falcon
> new file mode 100644
> index 0000000..94126fd
> --- /dev/null
> +++ b/doc/README.falcon
> @@ -0,0 +1,163 @@
> +U-Boot "Falcon" Mode
> +====================
> +
> +Introduction
> +------------
> +
> +This documents provides an overview 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,
>
In the text you have the offset to save the image onto a NAND offset so I
fail to see how it'd be used for SD-Card.
Can you elaborate it a bit?
> +and can be generalized seen as a way to start an image performing the
> minimum
> +required initialization. SPL initializes mainly the RAM controller, and
> after
> +that 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.
> +
> +Falcon adds a command under U-Boot to reuse all code responsible to
> prepare
> +the interface with the kernel. In usual U-boot systems, 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, this snapshot can be saved into persistent storage and SPL is
> +informed to load it before running the kernel.
>
You mix Falcon and falcon. I'd say you always use Falcon as it is the name
of the feature so it ought to be in upper case. Another thing, 'With
falcon, ' ought to be move to the previous line or have an empty line
before it.
> +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. Saves 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).
>
And for others?
> +3. Boot the board into "Falcon" mode. SPL will load the kernel and copy
> +the parameters 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.
>
An empty line before "The value"?
> +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_SPL_OS_BOOT Activate Falcon mode.
> + A board should implement the following functions:
> +
> +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
>
And other media?
> +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
> +
> +Function that a board must implement
> +------------------------------------
>
Is there others optional? Otherwise you could call it as:
Adding Falcon mode support for a board
+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] [fdt_addr if <img> = fdt] -
> export a kernel parameter image
> +
> +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.
> +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).
> +
> +Example (for the twister board):
> +--------------------------------
> +
> +Using mtd names and 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 2011. Slides are available at:
> +
> +http://schedule2012.rmll.info/IMG/pdf/LSM2012_UbootFalconMode_Babic.pdf
> --
> 1.7.9.5
>
>
Regards,
--
Otavio Salvador O.S. Systems
E-mail: otavio at ossystems.com.br http://www.ossystems.com.br
Mobile: +55 53 9981-7854 http://projetos.ossystems.com.br
More information about the U-Boot
mailing list