80 | | |
81 | | [=#distro-config] |
82 | | == Distro Config |
83 | | The Venice Bootloader uses U-Boot's 'Distro Config' which is a well defined U-Boot env intended to make it easier for distro maintainers to develop compatible bootscripts. This primarily entails a set of 'boot scripts' and variables that control them. |
84 | | |
85 | | Ultimately this U-Boot environment is looking for a U-Boot [#bootscript boot script] on a 'bootable' partition (partitions with the 'boot' flag enabled). It searches in this order with these rules: |
86 | | - **boot_targets** - list of target device type/nums to search: defaults to mmc1 mmc2 usb0 usb1 pxe |
87 | | - **devplist** - ''dynamically created'' list of all partitions flagged as 'bootable' |
88 | | - **boot_prefixes** - list of directories within a partition searched for bootscripts |
89 | | - **boot_scripts** - list of boot script names searched for |
90 | | |
91 | | |
92 | | [=#bootscript] |
93 | | == Boot Scripts |
94 | | When writing bootscripts compatible with [#distro-config Distro Config] you can assume the following env variables: |
95 | | - **devtype** - the device type the script was loaded from (mmc|usb|sata) |
96 | | - **devnum** - the device number the script was loaded from (ie 0 for mmc0, 1 for mmc1, etc) |
97 | | - **distro_bootpart** - the partition number the script was loaded from (ie 0, 1, etc) |
98 | | - **fdtcontroladdr** - the address the device-tree is at (Note that the Venice bootloader does not load/manipulate the device-tree itself - this is done by the SPL which loads/manipulates the device-tree and passes it to the bootloader) |
99 | | - **kernel_addr_r** - address where kernel can be loaded |
100 | | - **bootargs** - default bootargs to pass to the kernel - you probably want to add to this and not overwrite it |
101 | | - **console** - the serial console device to pass to the kernel |
102 | | |
103 | | Additionally you should note the following: |
104 | | - use load/ls/save commands which support FAT/ext filesystem types automatically instead of the fs specific commands |
105 | | - if using a root filesystem that is not supported by the bootloader (ie F2FS or BTRFS) you can place your bootscript and kernel image in the FAT12 filesystem on partition 1 of the boot device. This filesystem is part of the 16MB 'Boot Firmware' image. If doing so you will need to compress the kernel and package it into a [#fit FIT image] in order to fit it in the available space. |
106 | | |
107 | | The Distro-Config environment supports legacy uImage scripts (it does not support FIT images with scripts). You can create these with the {{{mkimage}}} tool from U-Boot as such: |
108 | | {{{#!bash |
109 | | mkimage -A arm64 -T script -C none -d boot.txt boot.scr |
110 | | }}} |
111 | | |
112 | | The bootscript can be updated at runtime on the Linux target. For example: |
113 | | {{{#!bash |
114 | | mkimage -A arm64 -T script -C none -d boot.txt /boot/boot.scr |
115 | | }}} |
116 | | |
117 | | |
118 | | [=#boot_targets] |
119 | | === Boot Device Order (boot_targets) |
120 | | While the Venice product family can only boot from its primary boot device (typically eMMC), once you are booted to the bootloader you can choose from a wider variety of devices to boot the OS from. |
121 | | |
122 | | This OS boot device order is specified by the [#distro-config Distro Config] environment. Specifically it is controlled by the {{{boot_targets}}} env variable which defaults to {{{mmc1 mmc2 usb0 usb1 pxe}}}. |
123 | | |
124 | | For example, to limit OS booting to only USB: |
125 | | {{{#!bash |
126 | | setenv boot_targets usb0 usb1 |
127 | | saveenv |
128 | | }}} |
129 | | |
130 | | |
131 | | [=#fit] |
132 | | == Flattened Image Tree (FIT) images |
133 | | The U-Boot bootloader supports Flattened Image Tree (FIT) images which expand greatly on the legacy U-Boot image (uImage) format by allowing multiple binary blobs within an image. These blobs can be kernel images, ramdisk images, device-tree blobs, and bootloader scripts. Each image can also be optionally compressed (meaning U-Boot will decompress it) and check-sumed with a variety of hash mechanisms (meaning U-Boot will verify the image before using it). |
134 | | |
135 | | Quick summary of FIT Images: |
136 | | * introduced to resolve limitations with original single-image formats and follow-on multi-image format supported by UBoot bootm (boot memory) |
137 | | * uses power of the Device-Tree-Compiler (DTC) |
138 | | * FIT .itb files can be created with mkimage by passing in a .its file which in device-tree notation describes the images |
139 | | * U-Boot supports FIT with several commands: |
140 | | - {{{source <addr>:<name>}}} # source a script by name from FIT image in memory |
141 | | - {{{iminfo <fitaddress>}}} # print all the info contained in a FIT image in memory and verify (just not boot it) |
142 | | - {{{imextract <fitaddress> <item> <addr>}}} # extract item (ie kernel@1) to addr |
143 | | - {{{bootm <fitaddress>[#conf] - $fdtcontroladdr}}} # boot default or 'conf' configuration (ie #config@1) |
144 | | - {{{bootm start <fitaddress>[#conf] - $fdtcontroladdr}}} # boot from memory a specific configuration (or default configuration) from FIT image |
145 | | |
146 | | Example: |
147 | | * kernel.its with a single compressed kernel for ARM64 |
148 | | {{{#!bash |
149 | | /dts-v1/; |
150 | | / { |
151 | | description = "Simple image with single Linux kernel"; |
152 | | #address-cells = <1>; |
153 | | images { |
154 | | kernel@1 { |
155 | | description = "Linux kernel"; |
156 | | data = /incbin/("./Image.gz"); |
157 | | type = "kernel"; |
158 | | arch = "arm64"; |
159 | | os = "linux"; |
160 | | compression = "gzip"; |
161 | | load = <0x40200000>; |
162 | | entry = <0x40200000>; |
163 | | hash@1 { |
164 | | algo = "sha256"; |
165 | | }; |
166 | | }; |
167 | | }; |
168 | | |
169 | | configurations { |
170 | | default = "conf@1"; |
171 | | conf@1 { |
172 | | description = "Boot Linux kernel"; |
173 | | kernel = "kernel@1"; |
174 | | }; |
175 | | }; |
176 | | }; |
177 | | }}} |
178 | | * create image: |
179 | | {{{#!bash |
180 | | cp arch/arm64/boot/Image . |
181 | | gzip Image |
182 | | mkimage -f kernel.its /tftpboot/kernel.itb |
183 | | }}} |
184 | | * boot the default configuration from U-Boot: |
185 | | {{{#!bash |
186 | | tftpboot $loadaddr kernel.itb && bootm $loadaddr - $fdtcontroladdr |
187 | | }}} |
188 | | |
189 | | References: |
190 | | * [http://git.denx.de/?p=u-boot.git;a=tree;f=doc/uImage.FIT doc/uImage.FIT] |
191 | | * http://www.denx.de/wiki/pub/U-Boot/Documentation/multi_image_booting_scenarios.pdf |
192 | | * http://elinux.org/images/f/f4/Elc2013_Fernandes.pdf |
193 | | |
194 | | |
195 | | = U-boot env tools |
196 | | A detailed description of u-boot-tools usage can be found [wiki:/ventana/bootloader#U-Bootenvtoolsfw_printenvfw_setenv here]. |
197 | | |
198 | | In order to configure u-boot-tools to work correctly for Venice you will need a fw_env.config file the appropriate values. |
199 | | |
200 | | To create this file: |
201 | | {{{#!bash |
202 | | cat << EOF > /etc/fw_env.config |
203 | | # Device offset Env. size |
204 | | /dev/mmcblk2 0xff0000 0x8000 |
205 | | /dev/mmcblk2 0xff8000 0x8000 |
206 | | EOF |
207 | | }}} |
208 | | |
| 80 | see [wiki:uboot] for more info |