The note is based on Linux version 5.15.43 in OpenBMC.
(TBD)
The virtual filesystem encompasses various file types, including character and block devices that serve as interfaces exposed to user space.
Typically, these device files are organized under the /dev/ directory.
By listing the files in this directory, we can observe the type, major number, and minor number associated with each file.
Alternatively, we can create device files in different locations using the mknod command, as long as we accurately specify the aforementioned attributes.
The behavior of these device files remains consistent regardless of their location.
root@romulus:~# ls -l /dev/
...
crw------- 1 root root 89, 1 Oct 23 04:00 /dev/i2c-1
crw------- 1 root root 89, 10 Oct 23 04:00 /dev/i2c-10
crw------- 1 root root 89, 11 Oct 23 04:00 /dev/i2c-11
...
brw-rw---- 1 root disk 31, 0 Oct 23 04:00 /dev/mtdblock0
brw-rw---- 1 root disk 31, 1 Oct 23 04:00 /dev/mtdblock1
brw-rw---- 1 root disk 31, 2 Oct 23 04:00 /dev/mtdblock2
| | |
v v v
file type major minor
Character files encompass a wide range of non-storage devices such as I2C, SPI, TTY, and more.
While the underlying devices may differ, applications interact with them using standard file operations similar to regular files.
However, the kernel does not provide uniform functions for managing these devices, as each driver has specific knowledge of how to handle its hardware.
Therefore, the kernel primarily offers the open function, which locates the corresponding driver based on the type, major, and minor numbers of the device.
-
open:- The virtual filesystem creates a
filestructure in kernel space, accessible through a file identifier from user space. - It identifies the target character device (
cdev) based on the provided type, major, and minor numbers, and retrieves the associated file operations (fops) from the corresponding device's table. - The specific file operations, which replace the default ones, are immediately attached to the opened file.
- The virtual filesystem creates a
-
read:- No default function is available for reading from character devices.
-
write:- No default function is available for writing to character devices.
-
ioctl:- No default function is available for performing ioctl operations on character devices.
More Details
struct inode {
umode_t i_mode; // file type: char or block
dev_t i_rdev; // dev#
union {
const struct file_operations *i_fop; // file operations
void (*free_inode)(struct inode *);
};
union {
struct pipe_inode_info *i_pipe;
struct cdev *i_cdev;
char *i_link;
unsigned i_dir_seq;
};
}const struct file_operations def_chr_fops = {
.open = chrdev_open,
.llseek = noop_llseek,
};+-------------+
| chrdev_open | :
+---|---------+
|
|--> if inode doesn't know where cdev is
|
|------> serach cdev in 'cdev_map' based on dev#
|
|------> save cdev addr in inode
|
|--> get file ops from cdev
|
| +--------------+
|--> | replace_fops | replace fops of file to cdev's
| +--------------+
|
+--> call ->open, e.g.,
+--------------+
| mtdchar_open |
+--------------+
struct cdev {
struct kobject kobj;
struct module *owner; // points to module if there's any
const struct file_operations *ops; // file operations
struct list_head list; // all inodes that represent the cdev are on the list
dev_t dev; // dev#
unsigned int count; // range of minor
} __randomize_layout;Block device files serve as uniform representations of storage devices such as hard drives, pen drives, NVMe drives, and non-persistent storage like ramdisks. Despite variations in medium and transfer protocols, they are primarily used for storing and retrieving files. However, accessing data from storage devices can be relatively slow compared to processor cache and memory. To address this limitation, optimizations have been implemented between the application and driver layers.
-
VFS Layer:
- Upon receiving the type, major, and minor numbers, the Virtual Filesystem (VFS) layer identifies the corresponding block device (bdev) and associates it with the
filefor subsequent operations. - Default operations, including
open,read,write, andioctl, are readily available at this layer.
- Upon receiving the type, major, and minor numbers, the Virtual Filesystem (VFS) layer identifies the corresponding block device (bdev) and associates it with the
-
Address Space:
- A file duplication, known as the page cache, is maintained in memory to facilitate faster operations while maintaining interfaces with the actual file stored on the storage medium.
- If the file does not exist in memory, it is read from the disk.
- Periodic or on-demand writes ensure that the file is eventually persisted on the disk.
-
Block Layer:
- The block layer includes a per-block device (bdev) queue, which temporarily holds requests, allowing the I/O scheduler to optimize their ordering before forwarding them to the driver.
-
Driver:
- The driver is responsible for transmitting the commands to the hardware controller, triggering the actual read and write actions on the storage device.
More Details
Surprise! Nothing is here; please refer to another page that hasn't existed!
The kernel encompasses a vast collection of drivers, which can be configured by users before building the kernel image. Various drivers, whether built-in or standalone modules, can be enabled to support specific hardware, such as the AST2500 chip. However, hardware configurations often differ, requiring flexibility in device support. To address this, developers introduced the concept of a device tree.
The device tree serves as a hierarchical structure, starting with the root node ("/"), where each node represents a device and includes generic or driver-specific properties. Instead of hard-coding device information into the kernel and building separate images for each hardware variant, device trees allow for dynamic configuration. Before booting the kernel, a specific device tree for the hardware configuration is selected. The kernel then parses the device tree and matches the drivers accordingly.
In our study case, the following terms are commonly associated with the device tree, along with their corresponding files:
-
Device Tree Source (DTS):
- A human-readable file used for writing and configuring the device tree.
- Example:
arch/arm/boot/dts/aspeed-bmc-opp-romulus.dts
-
Device Tree Source Include Files (DTSI):
- Files used by the DTS as a base, which can be included and overwritten as needed for specific nodes.
- Examples:
arch/arm/boot/dts/aspeed-g5.dtsi,arch/arm/boot/dts/openbmc-flash-layout.dtsi
-
Device Tree Blob (DTB):
- The binary representation of the device tree used by the kernel for parsing and device driver matching.
- Example:
arch/arm/boot/dts/aspeed-bmc-opp-romulus.dtb
More Details
ahb {
compatible = "simple-bus";
#address-cells = <1>; // 1 dword (4 bytes)
#size-cells = <1>; // 1 dword (4 bytes)
ranges; // so we interpret child node's reg as < 1 dword addr + 1 dword size, and so on >
fmc: spi@1e620000 {
reg = < 0x1e620000 0xc4 // a. 1 dword addr (0x1e620000) + 1 dword size (0xc4)
0x20000000 0x10000000 >; // b. 1 dword addr (0x20000000) + 1 dword size (0x10000000)
#address-cells = <1>;
#size-cells = <0>;
compatible = "aspeed,ast2500-fmc";
clocks = <&syscon ASPEED_CLK_AHB>;
status = "disabled";
interrupts = <19>; // c. hardware irq
platform_get_resource(pdev, IORESOURCE_MEM, 0); // access the MEM type resource with index = 0
platform_get_resource(pdev, IORESOURCE_MEM, 1); // access the MEM type resource with index = 1
platform_get_resource(pdev, IORESOURCE_IRQ, 0); // access the IRQ type resource with index = 0
dtc -I dtb -O dts arch/arm/boot/dts/aspeed-bmc-opp-romulus.dtb # construct dts from dtb
dtc -I fs -O dts /sys/firmware/devicetree/base # construct dts from filesystem (not that useful to me)
- List of devices added from DTB in function **of_platform_default_populate_init**
[ 0.180038] device: 'ahb': device_add
[ 0.198481] device: '1e620000.spi': device_add
[ 0.203438] device: '1e630000.spi': device_add
[ 0.204606] device: '1e6c2000.copro-interrupt-controller': device_add
[ 0.205406] device: '1e660000.ethernet': device_add
[ 0.206037] device: '1e6a0000.usb-vhub': device_add
[ 0.206468] device: 'ahb:apb': device_add
[ 0.207725] device: '1e6e2000.syscon': device_add
[ 0.209195] device: '1e6e207c.silicon-id': device_add
[ 0.209675] device: '1e6e2080.pinctrl': device_add
[ 0.210556] device: 'platform:1e6e2080.pinctrl--platform:1e6a0000.usb-vhub': device_add
[ 0.211799] device: 'platform:1e6e2080.pinctrl--platform:1e660000.ethernet': device_add
[ 0.212234] device: 'platform:1e6e2080.pinctrl--platform:1e630000.spi': device_add
[ 0.219286] device: '1e6e2078.hwrng': device_add
[ 0.220000] device: '1e6e6000.display': device_add
[ 0.220521] device: '1e6e9000.adc': device_add
[ 0.221058] device: '1e700000.video': device_add
[ 0.221494] device: '1e720000.sram': device_add
[ 0.224925] device: '1e780000.gpio': device_add
[ 0.226185] device: '1e782000.timer': device_add
[ 0.226842] device: '1e783000.serial': device_add
[ 0.227221] device: 'platform:1e6e2080.pinctrl--platform:1e783000.serial': device_add
[ 0.228314] device: '1e784000.serial': device_add
[ 0.228824] device: '1e785000.watchdog': device_add
[ 0.230142] device: '1e785020.watchdog': device_add
[ 0.230842] device: '1e786000.pwm-tacho-controller': device_add
[ 0.231402] device: 'platform:1e6e2080.pinctrl--platform:1e786000.pwm-tacho-controller': device_add
[ 0.233039] device: '1e787000.serial': device_add
[ 0.233714] device: '1e789000.lpc': device_add
[ 0.234579] device: '1e789080.lpc-ctrl': device_add
[ 0.235052] device: '1e789098.reset-controller': device_add
[ 0.235502] device: 'platform:1e789098.reset-controller--platform:1e783000.serial': device_add
[ 0.236189] device: '1e7890a0.lhc': device_add
[ 0.236727] device: '1e789140.ibt': device_add
[ 0.237134] device: 'ahb:apb:bus@1e78a000': device_add
[ 0.237557] device: 'platform:1e6e2080.pinctrl--platform:ahb:apb:bus@1e78a000': device_add
[ 0.238347] device: '1e78a080.i2c-bus': device_add
[ 0.238912] device: '1e78a0c0.i2c-bus': device_add
[ 0.239235] device: 'platform:1e6e2080.pinctrl--platform:1e78a0c0.i2c-bus': device_add
[ 0.240138] device: '1e78a100.i2c-bus': device_add
[ 0.240517] device: 'platform:1e6e2080.pinctrl--platform:1e78a100.i2c-bus': device_add
[ 0.241372] device: '1e78a140.i2c-bus': device_add
[ 0.241701] device: 'platform:1e6e2080.pinctrl--platform:1e78a140.i2c-bus': device_add
[ 0.242752] device: '1e78a180.i2c-bus': device_add
[ 0.243082] device: 'platform:1e6e2080.pinctrl--platform:1e78a180.i2c-bus': device_add
[ 0.244224] device: '1e78a1c0.i2c-bus': device_add
[ 0.244661] device: 'platform:1e6e2080.pinctrl--platform:1e78a1c0.i2c-bus': device_add
[ 0.245651] device: '1e78a300.i2c-bus': device_add
[ 0.246012] device: 'platform:1e6e2080.pinctrl--platform:1e78a300.i2c-bus': device_add
[ 0.246913] device: '1e78a340.i2c-bus': device_add
[ 0.247237] device: 'platform:1e6e2080.pinctrl--platform:1e78a340.i2c-bus': device_add
[ 0.248209] device: '1e78a380.i2c-bus': device_add
[ 0.248543] device: 'platform:1e6e2080.pinctrl--platform:1e78a380.i2c-bus': device_add
[ 0.249513] device: '1e78a3c0.i2c-bus': device_add
[ 0.249877] device: 'platform:1e6e2080.pinctrl--platform:1e78a3c0.i2c-bus': device_add
[ 0.251000] device: '1e78a400.i2c-bus': device_add
[ 0.251382] device: 'platform:1e6e2080.pinctrl--platform:1e78a400.i2c-bus': device_add
[ 0.252276] device: '1e78a440.i2c-bus': device_add
[ 0.252613] device: 'platform:1e6e2080.pinctrl--platform:1e78a440.i2c-bus': device_add
[ 0.253403] device: 'leds': device_add
[ 0.254278] device: 'platform:1e780000.gpio--platform:leds': device_add
[ 0.254838] device: 'gpio-fsi': device_add
[ 0.256303] device: 'platform:1e780000.gpio--platform:gpio-fsi': device_add
[ 0.256757] device: 'gpio-keys': device_add
[ 0.257201] device: 'platform:1e780000.gpio--platform:gpio-keys': device_add
[ 0.257606] device: 'iio-hwmon-battery': device_add
drivers/core/root.c
+------------------+
| dm_init_and_scan | : save udevice 'root' in gd, bind each enabled dev of dt to driver
+-|----------------+
| +---------+
|--> | dm_init | get udevice 'root' and save in gd
| +---------+
| +------------------+
|--> | dm_scan_platdata | (skip)
| +------------------+
| +----------------------+
|--> | dm_extended_scan_fdt | for each eanbled dev in dt: find target driver & prepare dev binding to it
| +----------------------+
| +---------------+
+--> | dm_scan_other | (skip)
+---------------+
drivers/core/root.c
+---------+
| dm_init | : get udevice 'root' and save in gd
+-|-------+ -
| +---------------------+
|--> | device_bind_by_name | given info (root info), get target udevice
| +---------------------+
| +--------------+
+--> | device_probe | (root driver has no ->probe() though)
+--------------+
drivers/core/root.c
+----------------------+
| dm_extended_scan_fdt | : for each eanbled dev in dt: find target driver & prepare dev binding to it
+-|--------------------+
| +-------------+
|--> | dm_scan_fdt | for each eanbled dev in dt: find target driver & prepare dev binding to it
| +-------------+
| +-------------------------+
|--> | dm_scan_fdt_ofnode_path | "/clocks"
| +-------------------------+
| +-------------------------+
+--> | dm_scan_fdt_ofnode_path | "/firmware"
+-------------------------+
drivers/core/root.c
+-------------+
| dm_scan_fdt | : for each eanbled dev in dt: find target driver & prepare dev binding to it
+-|-----------+
| +------------------+
+--> | dm_scan_fdt_node | : for each eanbled dev in dt: find target driver & prepare dev binding to it
+-|----------------+
|
+--> while we can still get a valid node
|
|--> get dt node name
|
|--> if it's 'chosen' or 'firmware', specially handle it and continue
|
|--> if it's not enabled, continue
|
| +----------------+
+--> | lists_bind_fdt | given dev compatible list, find target driver and prepare dev binding to that driver
+----------------+
drivers/core/lists.c
+----------------+
| lists_bind_fdt | : given dev compatible list, find target driver and prepare dev binding to that driver
+-|--------------+
|
|--> get compatible list
|
+--> for each value in list
|
|--> for each compiled-in driver
| |
| | +-------------------------+
| |--> | driver_check_compatible | check if driver supports compatible value
| | +-------------------------+
| |
| +--> if found, break
|
|--> if nothing found, continue
|
| +------------------------------+
|--> | device_bind_with_driver_data | prepare dev and bind to driver
| +------------------------------+
|
+--> pass dev back through argument
During the kernel initialization process, after the basic subsystems like process and memory management are set up, there are several categories of initialization calls that occur. These initialization calls are organized into different sections at the build stage, including:
- console_initcall
- early_initcall
- pure_initcall
- core_initcall
- postcore_initcall
- arch_initcall (includes device tree parsing function)
- subsys_initcall
- fs_initcall
- rootfs_initcall
- device_initcall
- late_initcall
The device tree parsing function is typically invoked during the arch_initcall section. Driver registrations, on the other hand, can happen in any of the sections. The order in which devices or drivers register is not crucial because the framework operates as follows:
- When a device is added, the framework searches for a matching driver by traversing the drivers on the same bus.
- Once a matching driver is found, it begins the probing process, initializing the software infrastructure of the device using information obtained from the corresponding device tree node.
- If the driver intends to make the probed device accessible to user space, it requests a specific or dynamically allocated range of device numbers. It prepares the character device (cdev) or block device (bdev) and inserts it into the appropriate table for later lookup by the open syscall.
- [log] console_initcall
(functions exist but print no log) - [log] early_initcall
[ 0.039965] Setting up static identity map for 0x80100000 - 0x80100078 [ 0.040797] rcu: Hierarchical SRCU implementation. [ 0.044779] ASPEED AST2500 rev A1 (04010303) - [log] pure_initcall
(functions exist but print no log) - [log] core_initcall
[ 0.076306] VFP support v0.3: implementor 41 architecture 1 part 20 variant b rev 5 [ 0.091632] clocksource: jiffies: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 19112604462750000 ns [ 0.092715] futex hash table entries: 256 (order: 2, 16384 bytes, linear) [ 0.098764] pinctrl core: initialized pinctrl subsystem [ 0.114512] NET: Registered PF_NETLINK/PF_ROUTE protocol family - [log] postcore_initcall
[ 0.125983] DMA: preallocated 256 KiB pool for atomic coherent allocations - [log] arch_initcall
[ 0.130412] hw-breakpoint: debug architecture 0x0 unsupported. - [log] subsys_initcall
[ 0.185670] Kprobes globally optimized [ 0.205378] SCSI subsystem initialized [ 0.206391] usbcore: registered new interface driver usbfs [ 0.206812] usbcore: registered new interface driver hub [ 0.207223] usbcore: registered new device driver usb [ 0.208119] mc: Linux media interface: v0.10 [ 0.208577] videodev: Linux video capture interface: v2.00 [ 0.209095] pps_core: LinuxPPS API ver. 1 registered [ 0.209419] pps_core: Software ver. 5.3.6 - Copyright 2005-2007 Rodolfo Giometti <giometti@linux.it> [ 0.210041] PTP clock support registered [ 0.210386] EDAC MC: Ver: 3.0.0 [ 0.221265] mctp: management component transport protocol core [ 0.221491] NET: Registered PF_MCTP protocol family - [log] fs_initcall
[ 0.232205] clocksource: Switched to clocksource FTTMR010-TIMER2 [ 0.286552] NET: Registered PF_INET protocol family [ 0.288124] IP idents hash table entries: 8192 (order: 4, 65536 bytes, linear) [ 0.291880] tcp_listen_portaddr_hash hash table entries: 512 (order: 0, 6144 bytes, linear) [ 0.292201] Table-perturb hash table entries: 65536 (order: 6, 262144 bytes, linear) [ 0.292481] TCP established hash table entries: 4096 (order: 2, 16384 bytes, linear) [ 0.292830] TCP bind hash table entries: 4096 (order: 3, 32768 bytes, linear) [ 0.293143] TCP: Hash tables configured (established 4096 bind 4096) [ 0.294303] UDP hash table entries: 256 (order: 1, 8192 bytes, linear) [ 0.294691] UDP-Lite hash table entries: 256 (order: 1, 8192 bytes, linear) [ 0.296047] NET: Registered PF_UNIX/PF_LOCAL protocol family - [log] rootfs_initcall
(functions exist but print no log) - [log] device_initcall (and module_init in some cases)
[ 0.303449] Unpacking initramfs... [ 0.324379] workingset: timestamp_bits=30 max_order=17 bucket_order=0 [ 0.333170] squashfs: version 4.0 (2009/01/31) Phillip Lougher [ 0.333798] jffs2: version 2.2. (SUMMARY) © 2001-2006 Red Hat, Inc. [ 0.335792] NET: Registered PF_ALG protocol family [ 0.348923] gpio-819 (nic_func_mode0): hogged as output/low [ 0.349182] gpio-820 (nic_func_mode1): hogged as output/low [ 0.349355] gpio-943 (seq_cont): hogged as output/low [ 0.365049] ipmi-bt-host 1e789140.ibt: Found bt bmc device [ 0.366584] ipmi-bt-host 1e789140.ibt: Using IRQ 34 [ 0.385032] Serial: 8250/16550 driver, 6 ports, IRQ sharing enabled [ 0.392850] 1e787000.serial: ttyS5 at MMIO 0x1e787000 (irq = 34, base_baud = 1546875) is a ASPEED VUART [ 0.407534] 1e783000.serial: ttyS0 at MMIO 0x1e783000 (irq = 32, base_baud = 1500000) is a 16550A [ 0.412622] 1e784000.serial: ttyS4 at MMIO 0x1e784000 (irq = 33, base_baud = 1500000) is a 16550A [ 0.414064] printk: console [ttyS4] enabled [ 0.414556] printk: bootconsole [ns16550a0] disabled [ 0.424346] timeriomem_rng 1e6e2078.hwrng: 32bits from 0x(ptrval) @ 1us [ 0.426618] aspeed_gfx 1e6e6000.display: assigned reserved memory node framebuffer [ 0.466909] [drm] Initialized aspeed-gfx-drm 1.0.0 20180319 for 1e6e6000.display on minor 0 [ 0.502691] aspeed_gfx 1e6e6000.display: [drm] fb0: aspeed-gfx-drmd frame buffer device [ 0.523210] loop: module loaded [ 0.540976] random: crng init done [ 0.586796] spi-nor spi0.0: n25q256a (32768 Kbytes) [ 1.344986] spi-aspeed-smc 1e620000.spi: CE0 read buswidth:2 [0x203b0641] [ 1.675808] Freeing initrd memory: 1076K [ 1.762860] 5 fixed-partitions partitions found on MTD device bmc [ 1.763113] Creating 5 MTD partitions on "bmc": [ 1.763369] 0x000000000000-0x000000060000 : "u-boot" [ 1.765620] 0x000000060000-0x000000080000 : "u-boot-env" [ 1.766919] 0x000000080000-0x0000004c0000 : "kernel" [ 1.768134] 0x0000004c0000-0x000001c00000 : "rofs" [ 1.769322] 0x000001c00000-0x000002000000 : "rwfs" [ 1.775133] spi-nor spi1.0: mx66l1g45g (131072 Kbytes) [ 1.775289] spi-aspeed-smc 1e630000.spi: CE0 window resized to 120MB (AST2500 HW quirk) [ 1.775864] spi-aspeed-smc 1e630000.spi: CE0 window (120MB) too small for mapping [ 1.783126] spi-aspeed-smc 1e630000.spi: Calibration area too uniform, using low speed [ 1.783342] spi-aspeed-smc 1e630000.spi: CE0 read buswidth:2 [0x203c0041] [ 1.829208] ftgmac100 1e660000.ethernet: Read MAC address 52:54:00:12:34:56 from chip [ 1.829612] ftgmac100 1e660000.ethernet: Using NCSI interface [ 1.842780] ftgmac100 1e660000.ethernet eth0: irq 20, mapped at 0a792023 [ 1.843482] MCTP I2C interface driver [ 1.843690] ehci_hcd: USB 2.0 'Enhanced' Host Controller (EHCI) Driver [ 1.843969] ehci-platform: EHCI generic platform driver [ 1.844593] usbcore: registered new interface driver usb-storage [ 1.845091] usbcore: registered new interface driver pl2303 [ 1.845426] usbserial: USB Serial support registered for pl2303 [ 1.860765] aspeed_vhub 1e6a0000.usb-vhub: Initialized virtual hub in USB2 mode [ 1.863027] i2c_dev: i2c /dev entries driver [ 1.865924] aspeed-i2c-bus 1e78a080.i2c-bus: i2c bus 1 registered, irq 35 [ 1.866938] aspeed-i2c-bus 1e78a0c0.i2c-bus: i2c bus 2 registered, irq 36 [ 1.867731] aspeed-i2c-bus 1e78a100.i2c-bus: i2c bus 3 registered, irq 37 [ 1.868507] aspeed-i2c-bus 1e78a140.i2c-bus: i2c bus 4 registered, irq 38 [ 1.869326] aspeed-i2c-bus 1e78a180.i2c-bus: i2c bus 5 registered, irq 39 [ 1.870070] aspeed-i2c-bus 1e78a1c0.i2c-bus: i2c bus 6 registered, irq 40 [ 1.870956] aspeed-i2c-bus 1e78a300.i2c-bus: i2c bus 7 registered, irq 41 [ 1.872189] aspeed-i2c-bus 1e78a340.i2c-bus: i2c bus 8 registered, irq 42 [ 1.873143] aspeed-i2c-bus 1e78a380.i2c-bus: i2c bus 9 registered, irq 43 [ 1.873938] aspeed-i2c-bus 1e78a3c0.i2c-bus: i2c bus 10 registered, irq 44 [ 1.879169] rtc-rv8803 11-0032: registered as rtc0 [ 1.880576] rtc-rv8803 11-0032: setting system clock to 2022-10-27T14:31:13 UTC (1666881073) [ 1.882506] aspeed-i2c-bus 1e78a400.i2c-bus: i2c bus 11 registered, irq 45 [ 1.883936] aspeed-i2c-bus 1e78a440.i2c-bus: i2c bus 12 registered, irq 46 [ 1.885895] aspeed-video 1e700000.video: assigned reserved memory node jpegbuffer [ 1.891435] Driver for 1-wire Dallas network protocol. [ 1.893721] w83773g 12-004c: error writing config rate register [ 1.900103] sdhci: Secure Digital Host Controller Interface driver [ 1.900259] sdhci: Copyright(c) Pierre Ossman [ 1.900362] sdhci-pltfm: SDHCI platform and OF driver helper [ 1.904658] usbcore: registered new interface driver usbhid [ 1.904878] usbhid: USB HID core driver [ 1.910429] SPI driver bmp280 has no spi_device_id for bosch,bmp085 [ 1.916138] fsi-master-acf gpio-fsi: ColdFire initialized, firmware v4 API v2.1 (trace disabled) [ 2.212752] fsi-master-acf gpio-fsi: Coprocessor startup timeout ! [ 2.233701] NET: Registered PF_INET6 protocol family [ 2.241406] Segment Routing with IPv6 [ 2.242001] In-situ OAM (IOAM) with IPv6 [ 2.243175] NET: Registered PF_PACKET protocol family [ 2.243544] 8021q: 802.1Q VLAN Support v1.8 - [log] late_initcall
[ 2.244279] Registering SWP/SWPB emulation handler [ 2.256221] printk: console [netcon0] enabled [ 2.256452] netconsole: network logging started [ 2.260362] input: gpio-keys as /devices/platform/gpio-keys/input/input0
More Details
drivers/char/mem.c
+--------------+
| chr_dev_init | : init char devices for mem, tty, and console
+-|------------+
| +-----------------+
|--> | register_chrdev | reserve dev# range, prepare cdev of the range and add to table
| +-----------------+
| +--------------+
|--> | class_create | create 'mem' class
| +--------------+
|
|--> for each minor of mem dev (e.g., null, zero, random, ...)
| |
| | +---------------+
| +--> | device_create | given params, create device
| +---------------+
| +----------+
+--> | tty_init | init char devices for tty and console
+----------+
+-------+ +-------+
┌──► | dev A | ◄────► | dev B |
subsys_private │ +-------+ +-------+
bus_type +---------------+ │
+---+ | klist_devices ◄──┘
| p ────────► | |
+---+ | klist_drivers ◄──┐
+---------------+ │
│ +-------+ +-------+ +-------+
└──► | drv C | ◄────► | drv D | ◄────► | drv E |
+-------+ +-------+ +-------+
struct bus_type {
const char *name; // name shown in /sys
int (*match)(struct device *dev, struct device_driver *drv); // attempt to find the matching driver for a given device
int (*probe)(struct device *dev); // link driver and device
void (*remove)(struct device *dev); // remove the unlink between driver and device
void (*shutdown)(struct device *dev); // power management operation
int (*suspend)(struct device *dev, pm_message_t state); // power management operation
int (*resume)(struct device *dev); // power management operation
struct subsys_private *p; // list heads for both drivers and devices
};+--------------+
| bus_register | : register bus and prepare files under /sys
+---|----------+
|
|--> alloc private
|
| +------------------+
|--> | kobject_set_name |
| +------------------+
| +---------------+
|--> | kset_register | add to bus subsystem
| +---------------+
| +-----------------+
|--> | bus_create_file | create files under /sys
| +-----------------+
| +---------------------+
|--> | kset_create_and_add | register "devices" kset to sysfs
| +---------------------+
| +---------------------+
|--> | kset_create_and_add | register "drivers" kset to sysfs
| +---------------------+
| +-----------------+
|--> | add_probe_files | create files under /sys
| +-----------------+
| +----------------+
+--> | bus_add_groups | create files under /sys
+----------------+
struct kobj_map {
struct probe {
struct probe *next; // singly linked list
dev_t dev; // dev# = (major, minor)
unsigned long range; // range of consecutive minor#
struct module *owner;
kobj_probe_t *get; // point to func that returns kobj
int (*lock)(dev_t, void *);
void *data; // points to struct cdev of gendisk
} *probes[255];
struct mutex *lock;
};
static struct char_device_struct {
struct char_device_struct *next; // singly linked list
unsigned int major; // major#
unsigned int baseminor; // smallest minor#
int minorct; // minor count = 'range' in kobj_map
char name[64]; // dev identifier
struct cdev *cdev; // points to cdev
} *chrdevs[CHRDEV_MAJOR_HASH_SIZE];
+-------------------+
| __register_chrdev | : reserve dev# range, prepare cdev of the range and add to table
+----|--------------+
| +--------------------------+
|--> | __register_chrdev_region | check if specified dev# range is available, reserve it if so
| +--------------------------+
|
|--> prepare a 'cdev' for the dev# range
|
| +----------+
+--> | cdev_add | add the 'cdev' to a table for later lookup
+----------+
+--------------------------+
| platform_driver_register | :
+------|-------------------+
|
|--> driver bus = platform_bus_type
|
| +-----------------+
+--> | driver_register | ensure driver is in bus, probe devices if newly registered
+-----------------+
+-----------------+
| driver_register | : ensure driver is in bus, probe devices if newly registered
+----|------------+
| +-------------+
|--> | driver_find | check if it's already registered
| +-------------+
| +----------------+
+--> | bus_add_driver | add driver to list of bus, probe devices to find match(es)
+----------------+
+----------------+
| bus_add_driver | : add driver to list of bus, probe devices to find match(es)
+---|------------+
|
|--> alloc private
|
|--> drvier kset = bus-driver kset
|
| +----------------+
|--> | klist_add_tail | add drvier to the driver list of bus
| +----------------+
|
|--> if bus 'auto probe' is labeled
|
| +---------------+
|------> | driver_attach | probe each device in bus to find the match
| +---------------+
|
+--> create files under /sys/
struct resource {
resource_size_t start; // start addr or irq
resource_size_t end; // end addr or irq
const char *name; // displays in /proc
unsigned long flags; // e.g., indicate the resource type
unsigned long desc;
struct resource *parent, *sibling, *child; // hierarchy
};struct device {
struct device *parent; // points to parent device
struct kobject kobj; // generic kobject framework
struct bus_type *bus; // points to the bus where the device belongs to
truct device_driver *driver; // points to the corresponding driver
void *platform_data; // private to platform code
void *driver_data; // private to driver code
void (*release)(struct device *dev); // release resource to kernel
};struct device_driver {
const char *name; // driver identifier
struct bus_type *bus; // points to the bus where the driver belongs to
int (*probe) (struct device *dev); // check if the driver can be applied to arg device
int (*remove) (struct device *dev); // call when device is removed
void (*shutdown) (struct device *dev); // power management related
int (*suspend) (struct device *dev, pm_message_t state); // power management related
int (*resume) (struct device *dev); // power management related
};+---------------------------------+
| of_platform_device_create_pdata |
+--------|------------------------+
| +-----------------+
|--> | of_device_alloc | prepare the structure of the device and resources
| +-----------------+
|
|--> set bus = platform_bus_type
|
| +---------------+
+--> | of_device_add |
+---------------+
+-----------------+
| device_register | : add to bus, send 'add dev' to notifier, probe device
+----|------------+
| +-------------------+
|--> | device_initialize |
| +-------------------+
| +------------+
+--> | device_add | add to bus, send 'add dev' to notifier, probe device
+------------+
+------------+
| device_add | : add to bus, send 'add dev' to notifier, probe device
+--|---------+
| +--------------+
|--> | dev_set_name |
| +--------------+
| +-------------+
+--> | kobject_add | register to device subsystem (kset is set in, e.g., device_initialize)
| +-------------+
| +----------------+
|--> | bus_add_device | create files in /sys, add device to list of bus
| +----------------+
| +----------------------+
|--> | devtmpfs_create_node | submit a request (create dev file) to devtmpfsd (a.k.a. "kdevtmpfs")
| +----------------------+
|
|--> if dev->bus is set
|
| +------------------------------+
|------> | blocking_notifier_call_chain | send event 'ADD_DEVICE' to notifier, e.g.,
| +------------------------------+ +----------------------+
| | i2cdev_notifier_call | action handler
| +----------------------+ e.g., if 'add device': prepare and register cdev
| +------------------+
+--> | bus_probe_device | traverse each driver and try to match, call driver->probe() if matched
| +------------------+
|
|--> if parent dev exists
|
| +----------------+
+------> | klist_add_tail | add dev to parent's children list
+----------------+
+----------------+
| bus_add_device | : create files in /sys, add device to list of bus
+---|------------+
| +-------------------+
|--> | sysfs_create_link | sysfs: create device in bus folder
| +-------------------+
| +-------------------+
|--> | sysfs_create_link | sysfs: create bus in device folder
| +-------------------+
| +----------------+
+--> | klist_add_tail | append the device to the device list of bus
+----------------+
+--------------+
| really_probe |
+---|----------+
| +-------------------+
|--> | pinctrl_bind_pins | switch pins to the expected state before probing if necessary
| +-------------------+
| +-------------------+
|--> | call_driver_probe | call bus->probe or driver->probe (most cases)
| +-------------------+
| +--------------+
+--> | driver_bound | attach the device to the driver, but not vice versa
+--------------+ (one driver might take care of multiple similar devices)
(devtmpfs, TBD)
- Check character devices that are exported to user space.
ls -l /sys/dev/char/ # display in (major: minor)
- Check block devices that are exported to user space.
ls -l /sys/dev/block/ # display in (major: minor)
ls -l /sys/block/ # display in name
- Check the IO layout.
cat /proc/iomem
cat /proc/ioports # empty in our study case
- Debug init calls.
# append initcall_debug to bootargs in dts
chosen {
stdout-path = &uart5;
bootargs = "console=ttyS4,115200 earlycon initcall_debug";
};
# rebuild the kernel with a larger log buffer if necessary
CONFIG_LOG_BUF_SHIFT=17
- Convert DTB to DTS.
dtc -I dtb -O dts arch/arm/boot/dts/aspeed-bmc-opp-romulus.dtb > dts.txt
- W. Mauerer, Professional Linux Kernel Architecture