From patchwork Tue Nov 13 11:11:35 2012 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Stefano Babic X-Patchwork-Id: 198632 X-Patchwork-Delegate: trini@ti.com Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Received: from theia.denx.de (theia.denx.de [85.214.87.163]) by ozlabs.org (Postfix) with ESMTP id 895EA2C0092 for ; Tue, 13 Nov 2012 22:12:12 +1100 (EST) Received: from localhost (localhost [127.0.0.1]) by theia.denx.de (Postfix) with ESMTP id A51854A087; Tue, 13 Nov 2012 12:12:06 +0100 (CET) X-Virus-Scanned: Debian amavisd-new at theia.denx.de Received: from theia.denx.de ([127.0.0.1]) by localhost (theia.denx.de [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id OIEfhIqMNNfO; Tue, 13 Nov 2012 12:12:06 +0100 (CET) Received: from theia.denx.de (localhost [127.0.0.1]) by theia.denx.de (Postfix) with ESMTP id 0784F4A057; Tue, 13 Nov 2012 12:12:03 +0100 (CET) Received: from localhost (localhost [127.0.0.1]) by theia.denx.de (Postfix) with ESMTP id 4D2484A036 for ; Tue, 13 Nov 2012 12:11:57 +0100 (CET) X-Virus-Scanned: Debian amavisd-new at theia.denx.de Received: from theia.denx.de ([127.0.0.1]) by localhost (theia.denx.de [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id tVxUSw1273Y6 for ; Tue, 13 Nov 2012 12:11:54 +0100 (CET) X-policyd-weight: NOT_IN_SBL_XBL_SPAMHAUS=-1.5 NOT_IN_SPAMCOP=-1.5 NOT_IN_BL_NJABL=-1.5 (only DNSBL check requested) Received: from smtpi4.ngi.it (smtpi4.ngi.it [88.149.128.104]) by theia.denx.de (Postfix) with ESMTP id 015914A029 for ; Tue, 13 Nov 2012 12:11:52 +0100 (CET) Received: from babic.homelinux.org (88-149-182-160.v4.ngi.it [88.149.182.160]) by smtpi4.ngi.it (Postfix) with ESMTP id E0F444218B; Tue, 13 Nov 2012 12:11:50 +0100 (CET) Received: from localhost (mail.babic.homelinux.org [127.0.0.1]) by babic.homelinux.org (Postfix) with ESMTP id D5B6E4540C44; Tue, 13 Nov 2012 12:11:49 +0100 (CET) X-Virus-Scanned: Debian amavisd-new at babicengineering.eu Received: from babic.homelinux.org ([127.0.0.1]) by localhost (mail.babic.homelinux.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id 21NMbwKl8P1s; Tue, 13 Nov 2012 12:11:41 +0100 (CET) Received: from papero.lan (papero.lan [192.168.2.247]) by babic.homelinux.org (Postfix) with ESMTP id 5A6924540C36; Tue, 13 Nov 2012 12:11:41 +0100 (CET) From: Stefano Babic To: U-Boot Mailing List Date: Tue, 13 Nov 2012 12:11:35 +0100 Message-Id: <1352805097-23042-1-git-send-email-sbabic@denx.de> X-Mailer: git-send-email 1.7.9.5 In-Reply-To: <1352717979-6284-1-git-send-email-sbabic@denx.de> References: <1352717979-6284-1-git-send-email-sbabic@denx.de> Cc: Tom Rini , marex@denx.de, otavio@ossystems.com.br Subject: [U-Boot] [PATCH v2 1/2] Add README for the "Falcon" mode X-BeenThere: u-boot@lists.denx.de X-Mailman-Version: 2.1.11 Precedence: list List-Id: U-Boot discussion List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , MIME-Version: 1.0 Sender: u-boot-bounces@lists.denx.de Errors-To: u-boot-bounces@lists.denx.de Simple howto to add support to a board for booting the kernel from SPL ("Falcon" mode). Signed-off-by: Stefano Babic --- 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, +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. + +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). + +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. + +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 + 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 + +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 [kernel_addr] [fdt_addr if = 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 , # 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