diff options
Diffstat (limited to 'doc')
| -rw-r--r-- | doc/README.efi | 237 | ||||
| -rw-r--r-- | doc/README.x86 | 324 | ||||
| -rw-r--r-- | doc/device-tree-bindings/misc/intel,irq-router.txt | 4 | ||||
| -rw-r--r-- | doc/driver-model/pci-info.txt | 6 |
4 files changed, 566 insertions, 5 deletions
diff --git a/doc/README.efi b/doc/README.efi new file mode 100644 index 0000000..7c95579 --- /dev/null +++ b/doc/README.efi @@ -0,0 +1,237 @@ +# +# Copyright (C) 2015 Google, Inc +# +# SPDX-License-Identifier: GPL-2.0+ +# + +U-Boot on EFI +============= +This document provides information about U-Boot running on top of EFI, either +as an application or just as a means of getting U-Boot onto a new platform. + + +In God's Name, Why? +------------------- +This is useful in several situations: + +- You have EFI running on a board but U-Boot does not natively support it +fully yet. You can boot into U-Boot from EFI and use that until U-Boot is +fully ported + +- You need to use an EFI implementation (e.g. UEFI) because your vendor +requires it in order to provide support + +- You plan to use coreboot to boot into U-Boot but coreboot support does +not currently exist for your platform. In the meantime you can use U-Boot +on EFI and then move to U-Boot on coreboot when ready + +- You use EFI but want to experiment with a simpler alternative like U-Boot + + +Status +------ +Only x86 is supported at present. If you are using EFI on another architecture +you may want to reconsider. However, much of the code is generic so could be +ported. + +U-Boot supports running as an EFI application for 32-bit EFI only. This is +not very useful since only a serial port is provided. You can look around at +memory and type 'help' but that is about it. + +More usefully, U-Boot supports building itself as a payload for either 32-bit +or 64-bit EFI. U-Boot is packaged up and loaded in its entirety by EFI. Once +started, U-Boot changes to 32-bit mode (currently) and takes over the +machine. You can use devices, boot a kernel, etc. + + +Build Instructions +------------------ +First choose a board that has EFI support and obtain an EFI implementation +for that board. It will be either 32-bit or 64-bit. + +To build U-Boot as an EFI application (32-bit EFI required), enable +CONFIG_EFI and CONFIG_EFI_APP. The efi-x86 config is set up for this. + +To build U-Boot as an EFI payload (32-bit or 64-bit EFI can be used), adjust +an existing config to enable CONFIG_EFI, CONFIG_EFI_STUB and either +CONFIG_EFI_STUB_32BIT or CONFIG_EFI_STUB_64BIT. + +Then build U-Boot as normal, e.g. + + make qemu-x86_defconfig + make menuconfig (or make xconfig if you prefer) + # change the settings as above + make + +You will end up with one of these files: + + u-boot-app.efi - U-Boot EFI application + u-boot-payload.efi - U-Boot EFI payload application + + +Trying it out +------------- +Qemu is an emulator and it can emulate an x86 machine. You can run the +payload with something like this: + + mkdir /tmp/efi + cp /path/to/u-boot*.efi /tmp/efi + qemu-system-x86_64 -bios bios.bin -hda fat:/tmp/efi/ + +Add -nographic if you want to use the terminal for output. Once it starts +type 'fs0:u-boot-payload.efi' to run the payload or 'fs0:u-boot-app.efi' to +run the application. 'bios.bin' is the EFI 'BIOS'. + +To try it on real hardware, put u-boot-app.efi on a suitable boot medium, +such as a USB stick. Then you can type something like this to start it: + + fs0:u-boot-payload.efi + +(or fs0:u-boot-app.efi for the application) + +This will start the payload, copy U-Boot into RAM and start U-Boot. Note +that EFI does not support booting a 64-bit application from a 32-bit +EFI (or vice versa). Also it will often fail to print an error message if +you get this wrong. + + +Inner workings +============== +Here follow a few implementation notes for those who want to fiddle with +this and perhaps contribute patches. + +The application and payload approaches sound similar but are in fact +implemented completely differently. + +EFI Application +--------------- +For the application the whole of U-Boot is built as a shared library. The +efi_main() function is in lib/efi/efi_app.c. It sets up some basic EFI +functions with efi_init(), sets up U-Boot global_data, allocates memory for +U-Boot's malloc(), etc. and enters the normal init sequence (board_init_f() +and board_init_r()). + +Since U-Boot limits its memory access to the allocated regions very little +special code is needed. The CONFIG_EFI_APP option controls a few things +that need to change so 'git grep CONFIG_EFI_APP' may be instructive. +The CONFIG_EFI option controls more general EFI adjustments. + +The only available driver is the serial driver. This calls back into EFI +'boot services' to send and receive characters. Although it is implemented +as a serial driver the console device is not necessarilly serial. If you +boot EFI with video output then the 'serial' device will operate on your +target devices's display instead and the device's USB keyboard will also +work if connected. If you have both serial and video output, then both +consoles will be active. Even though U-Boot does the same thing normally, +These are features of EFI, not U-Boot. + +Very little code is involved in implementing the EFI application feature. +U-Boot is highly portable. Most of the difficulty is in modifying the +Makefile settings to pass the right build flags. In particular there is very +little x86-specific code involved - you can find most of it in +arch/x86/cpu. Porting to ARM (which can also use EFI if you are brave +enough) should be straightforward. + +Use the 'reset' command to get back to EFI. + +EFI Payload +----------- +The payload approach is a different kettle of fish. It works by building +U-Boot exactly as normal for your target board, then adding the entire +image (including device tree) into a small EFI stub application responsible +for booting it. The stub application is built as a normal EFI application +except that it has a lot of data attached to it. + +The stub application is implemented in lib/efi/efi_stub.c. The efi_main() +function is called by EFI. It is responsible for copying U-Boot from its +original location into memory, disabling EFI boot services and starting +U-Boot. U-Boot then starts as normal, relocates, starts all drivers, etc. + +The stub application is architecture-dependent. At present it has some +x86-specific code and a comment at the top of efi_stub.c describes this. + +While the stub application does allocate some memory from EFI this is not +used by U-Boot (the payload). In fact when U-Boot starts it has all of the +memory available to it and can operate as it pleases (but see the next +section). + +Tables +------ +The payload can pass information to U-Boot in the form of EFI tables. At +present this feature is used to pass the EFI memory map, an inordinately +large list of memory regions. You can use the 'efi mem all' command to +display this list. U-Boot uses the list to work out where to relocate +itself. + +Although U-Boot can use any memory it likes, EFI marks some memory as used +by 'run-time services', code that hangs around while U-Boot is running and +is even present when Linux is running. This is common on x86 and provides +a way for Linux to call back into the firmware to control things like CPU +fan speed. U-Boot uses only 'conventional' memory, in EFI terminology. It +will relocate itself to the top of the largest block of memory it can find +below 4GB. + +Interrupts +---------- +U-Boot drivers typically don't use interrupts. Since EFI enables interrupts +it is possible that an interrupt will fire that U-Boot cannot handle. This +seems to cause problems. For this reason the U-Boot payload runs with +interrupts disabled at present. + +32/64-bit +--------- +While the EFI application can in principle be built as either 32- or 64-bit, +only 32-bit is currently supported. This means that the application can only +be used with 32-bit EFI. + +The payload stub can be build as either 32- or 64-bits. Only a small amount +of code is built this way (see the extra- line in lib/efi/Makefile). +Everything else is built as a normal U-Boot, so is always 32-bit on x86 at +present. + +Future work +----------- +This work could be extended in a number of ways: + +- Add a generic x86 EFI payload configuration. At present you need to modify +an existing one, but mostly the low-level x86 code is disabled when booting +on EFI anyway, so a generic 'EFI' board could be created with a suitable set +of drivers enabled. + +- Add ARM support + +- Add 64-bit application support + +- Figure out how to solve the interrupt problem + +- Add more drivers to the application side (e.g. video, block devices, USB, +environment access). This would mostly be an academic exercise as a strong +use case is not readily apparent, but it might be fun. + +- Avoid turning off boot services in the stub. Instead allow U-Boot to make +use of boot services in case it wants to. It is unclear what it might want +though. + +Where is the code? +------------------ +lib/efi + payload stub, application, support code. Mostly arch-neutral + +arch/x86/lib/efi + helper functions for the fake DRAM init, etc. These can be used by + any board that runs as a payload. + +arch/x86/cpu/efi + x86 support code for running as an EFI application + +board/efi/efi-x86/efi.c + x86 board code for running as an EFI application + +common/cmd_efi.c + the 'efi' command + + +-- +Ben Stoltz, Simon Glass +Google, Inc +July 2015 diff --git a/doc/README.x86 b/doc/README.x86 index 5d71244..af2459c 100644 --- a/doc/README.x86 +++ b/doc/README.x86 @@ -281,6 +281,11 @@ QEMU emulates a graphic card which U-Boot supports. Removing '-nographic' will show QEMU's VGA console window. Note this will disable QEMU's serial output. If you want to check both consoles, use '-serial stdio'. +Multicore is also supported by QEMU via '-smp n' where n is the number of cores +to instantiate. Currently the default U-Boot built for QEMU supports 2 cores. +In order to support more cores, you need add additional cpu nodes in the device +tree and change CONFIG_MAX_CPUS accordingly. + CPU Microcode ------------- Modern CPUs usually require a special bit stream called microcode [8] to be @@ -325,6 +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. @@ -388,6 +668,46 @@ boot progress. This can be good for debugging. If not, you can try to get serial working as early as possible. The early debug serial port may be useful here. See setup_early_uart() for an example. +During the U-Boot porting, one of the important steps is to write correct PIRQ +routing information in the board device tree. Without it, device drivers in the +Linux kernel won't function correctly due to interrupt is not working. Please +refer to U-Boot doc [14] for the device tree bindings of Intel interrupt router. +Here we have more details on the intel,pirq-routing property below. + + intel,pirq-routing = < + PCI_BDF(0, 2, 0) INTA PIRQA + ... + >; + +As you see each entry has 3 cells. For the first one, we need describe all pci +devices mounted on the board. For SoC devices, normally there is a chapter on +the chipset datasheet which lists all the available PCI devices. For example on +Bay Trail, this is chapter 4.3 (PCI configuration space). For the second one, we +can get the interrupt pin either from datasheet or hardware via U-Boot shell. +The reliable source is the hardware as sometimes chipset datasheet is not 100% +up-to-date. Type 'pci header' plus the device's pci bus/device/function number +from U-Boot shell below. + + => pci header 0.1e.1 + vendor ID = 0x8086 + device ID = 0x0f08 + ... + interrupt line = 0x09 + interrupt pin = 0x04 + ... + +It shows this PCI device is using INTD pin as it reports 4 in the interrupt pin +register. Repeat this until you get interrupt pins for all the devices. The last +cell is the PIRQ line which a particular interrupt pin is mapped to. On Intel +chipset, the power-up default mapping is INTA/B/C/D maps to PIRQA/B/C/D. This +can be changed by registers in LPC bridge. So far Intel FSP does not touch those +registers so we can write down the PIRQ according to the default mapping rule. + +Once we get the PIRQ routing information in the device tree, the interrupt +allocation and assignment will be done by U-Boot automatically. Now you can +enable CONFIG_GENERATE_PIRQ_TABLE for testing Linux kernel using i8259 PIC and +CONFIG_GENERATE_MP_TABLE for testing Linux kernel using local APIC and I/O APIC. + TODO List --------- - Audio @@ -406,3 +726,7 @@ 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 +[14] doc/device-tree-bindings/misc/intel,irq-router.txt diff --git a/doc/device-tree-bindings/misc/intel,irq-router.txt b/doc/device-tree-bindings/misc/intel,irq-router.txt index 598b4b1..e4d8ead 100644 --- a/doc/device-tree-bindings/misc/intel,irq-router.txt +++ b/doc/device-tree-bindings/misc/intel,irq-router.txt @@ -17,8 +17,8 @@ Required properties : - intel,pirq-link : Specifies the PIRQ link information with two cells. The first cell is the register offset that controls the first PIRQ link routing. The second cell is the total number of PIRQ links the router supports. -- intel,pirq-mask : Specifies the IRQ mask reprenting the 16 IRQs in 8259 PIC. - Bit N is 1 means IRQ N is available to be routed. +- intel,pirq-mask : Specifies the IRQ mask representing the 16 IRQs in the + 8259 PIC. Bit N is 1 means IRQ N is available to be routed. - intel,pirq-routing : Specifies all PCI devices' IRQ routing information, encoded as 3 cells a group for a device. The first cell is the device's PCI bus number, device number and function number encoding with PCI_BDF() macro. diff --git a/doc/driver-model/pci-info.txt b/doc/driver-model/pci-info.txt index 63efcb7..cf69167 100644 --- a/doc/driver-model/pci-info.txt +++ b/doc/driver-model/pci-info.txt @@ -6,7 +6,7 @@ How busses are scanned Any config read will end up at pci_read_config(). This uses uclass_get_device_by_seq() to get the PCI bus for a particular bus number. -Bus number 0 will need to be requested first, and the alias in the device +Bus number 0 will need to be requested first, and the alias in the device tree file will point to the correct device: @@ -23,7 +23,7 @@ tree file will point to the correct device: If there is no alias the devices will be numbered sequentially in the device tree. -The call to uclass_get_device by seq() will cause the PCI bus to be probed. +The call to uclass_get_device() will cause the PCI bus to be probed. This does a scan of the bus to locate available devices. These devices are bound to their appropriate driver if available. If there is no driver, then they are bound to a generic PCI driver which does nothing. @@ -32,7 +32,7 @@ After probing a bus, the available devices will appear in the device tree under that bus. Note that this is all done on a lazy basis, as needed, so until something is -touched on PCI it will not be probed. +touched on PCI (eg: a call to pci_find_devices()) it will not be probed. PCI devices can appear in the device tree. If they do this serves to specify the driver to use for the device. In this case they will be bound at |