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diff --git a/doc/README.x86 b/doc/README.x86 index 1cab42c..00b3ed0 100644 --- a/doc/README.x86 +++ b/doc/README.x86 @@ -330,6 +330,281 @@ mtrr - List and set the Memory Type Range Registers (MTRR). These are used to mode to use. U-Boot sets up some reasonable values but you can adjust then with this command. +Booting Ubuntu +-------------- +As an example of how to set up your boot flow with U-Boot, here are +instructions for starting Ubuntu from U-Boot. These instructions have been +tested on Minnowboard MAX with a SATA driver but are equally applicable on +other platforms and other media. There are really only four steps and its a +very simple script, but a more detailed explanation is provided here for +completeness. + +Note: It is possible to set up U-Boot to boot automatically using syslinux. +It could also use the grub.cfg file (/efi/ubuntu/grub.cfg) to obtain the +GUID. If you figure these out, please post patches to this README. + +Firstly, you will need Ubunutu installed on an available disk. It should be +possible to make U-Boot start a USB start-up disk but for now let's assume +that you used another boot loader to install Ubuntu. + +Use the U-Boot command line to find the UUID of the partition you want to +boot. For example our disk is SCSI device 0: + +=> part list scsi 0 + +Partition Map for SCSI device 0 -- Partition Type: EFI + + Part Start LBA End LBA Name + Attributes + Type GUID + Partition GUID + 1 0x00000800 0x001007ff "" + attrs: 0x0000000000000000 + type: c12a7328-f81f-11d2-ba4b-00a0c93ec93b + guid: 9d02e8e4-4d59-408f-a9b0-fd497bc9291c + 2 0x00100800 0x037d8fff "" + attrs: 0x0000000000000000 + type: 0fc63daf-8483-4772-8e79-3d69d8477de4 + guid: 965c59ee-1822-4326-90d2-b02446050059 + 3 0x037d9000 0x03ba27ff "" + attrs: 0x0000000000000000 + type: 0657fd6d-a4ab-43c4-84e5-0933c84b4f4f + guid: 2c4282bd-1e82-4bcf-a5ff-51dedbf39f17 + => + +This shows that your SCSI disk has three partitions. The really long hex +strings are called Globally Unique Identifiers (GUIDs). You can look up the +'type' ones here [11]. On this disk the first partition is for EFI and is in +VFAT format (DOS/Windows): + + => fatls scsi 0:1 + efi/ + + 0 file(s), 1 dir(s) + + +Partition 2 is 'Linux filesystem data' so that will be our root disk. It is +in ext2 format: + + => ext2ls scsi 0:2 + <DIR> 4096 . + <DIR> 4096 .. + <DIR> 16384 lost+found + <DIR> 4096 boot + <DIR> 12288 etc + <DIR> 4096 media + <DIR> 4096 bin + <DIR> 4096 dev + <DIR> 4096 home + <DIR> 4096 lib + <DIR> 4096 lib64 + <DIR> 4096 mnt + <DIR> 4096 opt + <DIR> 4096 proc + <DIR> 4096 root + <DIR> 4096 run + <DIR> 12288 sbin + <DIR> 4096 srv + <DIR> 4096 sys + <DIR> 4096 tmp + <DIR> 4096 usr + <DIR> 4096 var + <SYM> 33 initrd.img + <SYM> 30 vmlinuz + <DIR> 4096 cdrom + <SYM> 33 initrd.img.old + => + +and if you look in the /boot directory you will see the kernel: + + => ext2ls scsi 0:2 /boot + <DIR> 4096 . + <DIR> 4096 .. + <DIR> 4096 efi + <DIR> 4096 grub + 3381262 System.map-3.13.0-32-generic + 1162712 abi-3.13.0-32-generic + 165611 config-3.13.0-32-generic + 176500 memtest86+.bin + 178176 memtest86+.elf + 178680 memtest86+_multiboot.bin + 5798112 vmlinuz-3.13.0-32-generic + 165762 config-3.13.0-58-generic + 1165129 abi-3.13.0-58-generic + 5823136 vmlinuz-3.13.0-58-generic + 19215259 initrd.img-3.13.0-58-generic + 3391763 System.map-3.13.0-58-generic + 5825048 vmlinuz-3.13.0-58-generic.efi.signed + 28304443 initrd.img-3.13.0-32-generic + => + +The 'vmlinuz' files contain a packaged Linux kernel. The format is a kind of +self-extracting compressed file mixed with some 'setup' configuration data. +Despite its size (uncompressed it is >10MB) this only includes a basic set of +device drivers, enough to boot on most hardware types. + +The 'initrd' files contain a RAM disk. This is something that can be loaded +into RAM and will appear to Linux like a disk. Ubuntu uses this to hold lots +of drivers for whatever hardware you might have. It is loaded before the +real root disk is accessed. + +The numbers after the end of each file are the version. Here it is Linux +version 3.13. You can find the source code for this in the Linux tree with +the tag v3.13. The '.0' allows for additional Linux releases to fix problems, +but normally this is not needed. The '-58' is used by Ubuntu. Each time they +release a new kernel they increment this number. New Ubuntu versions might +include kernel patches to fix reported bugs. Stable kernels can exist for +some years so this number can get quite high. + +The '.efi.signed' kernel is signed for EFI's secure boot. U-Boot has its own +secure boot mechanism - see [12] [13] and cannot read .efi files at present. + +To boot Ubuntu from U-Boot the steps are as follows: + +1. Set up the boot arguments. Use the GUID for the partition you want to +boot: + + => setenv bootargs root=/dev/disk/by-partuuid/965c59ee-1822-4326-90d2-b02446050059 ro + +Here root= tells Linux the location of its root disk. The disk is specified +by its GUID, using '/dev/disk/by-partuuid/', a Linux path to a 'directory' +containing all the GUIDs Linux has found. When it starts up, there will be a +file in that directory with this name in it. It is also possible to use a +device name here, see later. + +2. Load the kernel. Since it is an ext2/4 filesystem we can do: + + => ext2load scsi 0:2 03000000 /boot/vmlinuz-3.13.0-58-generic + +The address 30000000 is arbitrary, but there seem to be problems with using +small addresses (sometimes Linux cannot find the ramdisk). This is 48MB into +the start of RAM (which is at 0 on x86). + +3. Load the ramdisk (to 64MB): + + => ext2load scsi 0:2 04000000 /boot/initrd.img-3.13.0-58-generic + +4. Start up the kernel. We need to know the size of the ramdisk, but can use +a variable for that. U-Boot sets 'filesize' to the size of the last file it +loaded. + + => zboot 03000000 0 04000000 ${filesize} + +Type 'help zboot' if you want to see what the arguments are. U-Boot on x86 is +quite verbose when it boots a kernel. You should see these messages from +U-Boot: + + Valid Boot Flag + Setup Size = 0x00004400 + Magic signature found + Using boot protocol version 2.0c + Linux kernel version 3.13.0-58-generic (buildd@allspice) #97-Ubuntu SMP Wed Jul 8 02:56:15 UTC 2015 + Building boot_params at 0x00090000 + Loading bzImage at address 100000 (5805728 bytes) + Magic signature found + Initial RAM disk at linear address 0x04000000, size 19215259 bytes + Kernel command line: "console=ttyS0,115200 root=/dev/disk/by-partuuid/965c59ee-1822-4326-90d2-b02446050059 ro" + + Starting kernel ... + +U-Boot prints out some bootstage timing. This is more useful if you put the +above commands into a script since then it will be faster. + + Timer summary in microseconds: + Mark Elapsed Stage + 0 0 reset + 241,535 241,535 board_init_r + 2,421,611 2,180,076 id=64 + 2,421,790 179 id=65 + 2,428,215 6,425 main_loop + 48,860,584 46,432,369 start_kernel + + Accumulated time: + 240,329 ahci + 1,422,704 vesa display + +Now the kernel actually starts: + + [ 0.000000] Initializing cgroup subsys cpuset + [ 0.000000] Initializing cgroup subsys cpu + [ 0.000000] Initializing cgroup subsys cpuacct + [ 0.000000] Linux version 3.13.0-58-generic (buildd@allspice) (gcc version 4.8.2 (Ubuntu 4.8.2-19ubuntu1) ) #97-Ubuntu SMP Wed Jul 8 02:56:15 UTC 2015 (Ubuntu 3.13.0-58.97-generic 3.13.11-ckt22) + [ 0.000000] Command line: console=ttyS0,115200 root=/dev/disk/by-partuuid/965c59ee-1822-4326-90d2-b02446050059 ro + +It continues for a long time. Along the way you will see it pick up your +ramdisk: + + [ 0.000000] RAMDISK: [mem 0x04000000-0x05253fff] +... + [ 0.788540] Trying to unpack rootfs image as initramfs... + [ 1.540111] Freeing initrd memory: 18768K (ffff880004000000 - ffff880005254000) +... + +Later it actually starts using it: + + Begin: Running /scripts/local-premount ... done. + +You should also see your boot disk turn up: + + [ 4.357243] scsi 1:0:0:0: Direct-Access ATA ADATA SP310 5.2 PQ: 0 ANSI: 5 + [ 4.366860] sd 1:0:0:0: [sda] 62533296 512-byte logical blocks: (32.0 GB/29.8 GiB) + [ 4.375677] sd 1:0:0:0: Attached scsi generic sg0 type 0 + [ 4.381859] sd 1:0:0:0: [sda] Write Protect is off + [ 4.387452] sd 1:0:0:0: [sda] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA + [ 4.399535] sda: sda1 sda2 sda3 + +Linux has found the three partitions (sda1-3). Mercifully it doesn't print out +the GUIDs. In step 1 above we could have used: + + setenv bootargs root=/dev/sda2 ro + +instead of the GUID. However if you add another drive to your board the +numbering may change whereas the GUIDs will not. So if your boot partition +becomes sdb2, it will still boot. For embedded systems where you just want to +boot the first disk, you have that option. + +The last thing you will see on the console is mention of plymouth (which +displays the Ubuntu start-up screen) and a lot of 'Starting' messages: + + * Starting Mount filesystems on boot [ OK ] + +After a pause you should see a login screen on your display and you are done. + +If you want to put this in a script you can use something like this: + + setenv bootargs root=UUID=b2aaf743-0418-4d90-94cc-3e6108d7d968 ro + setenv boot zboot 03000000 0 04000000 \${filesize} + setenv bootcmd "ext2load scsi 0:2 03000000 /boot/vmlinuz-3.13.0-58-generic; ext2load scsi 0:2 04000000 /boot/initrd.img-3.13.0-58-generic; run boot" + saveenv + +The \ is to tell the shell not to evaluate ${filesize} as part of the setenv +command. + +You will also need to add this to your board configuration file, e.g. +include/configs/minnowmax.h: + + #define CONFIG_BOOTDELAY 2 + +Now when you reset your board it wait a few seconds (in case you want to +interrupt) and then should boot straight into Ubuntu. + +You can also bake this behaviour into your build by hard-coding the +environment variables if you add this to minnowmax.h: + +#undef CONFIG_BOOTARGS +#undef CONFIG_BOOTCOMMAND + +#define CONFIG_BOOTARGS \ + "root=/dev/sda2 ro" +#define CONFIG_BOOTCOMMAND \ + "ext2load scsi 0:2 03000000 /boot/vmlinuz-3.13.0-58-generic; " \ + "ext2load scsi 0:2 04000000 /boot/initrd.img-3.13.0-58-generic; " \ + "run boot" + +#undef CONFIG_EXTRA_ENV_SETTINGS +#define CONFIG_EXTRA_ENV_SETTINGS "boot=zboot 03000000 0 04000000 ${filesize}" + + Development Flow ---------------- These notes are for those who want to port U-Boot to a new x86 platform. @@ -411,3 +686,6 @@ References [8] http://en.wikipedia.org/wiki/Microcode [9] http://simplefirmware.org [10] http://www.intel.com/design/archives/processors/pro/docs/242016.htm +[11] https://en.wikipedia.org/wiki/GUID_Partition_Table +[12] http://events.linuxfoundation.org/sites/events/files/slides/chromeos_and_diy_vboot_0.pdf +[13] http://events.linuxfoundation.org/sites/events/files/slides/elce-2014.pdf |