Linux內(nèi)核6.10提供了對沒有mmu的riscv處理器工作在S模式下的內(nèi)核的支持，本文介紹基于OpenSBI的linux no mmu的實現(xiàn)，供大家參考。

1、OpenSBI介紹

SBI：Supervisor Software Binary Interface 軟件二進制接口

Linux內(nèi)核工作在S模式下時，不能直接訪問機器定時器。而系統(tǒng)的運行依賴于定時器，為了解決這個問題，需要通過SBI接口由工作在M模式下的SBI固件來提供訪問定時器等功能。

SBI的實現(xiàn)方式有很多種，常見的包括BBL、OpenSBI、Xvisor、KVM、RustSBI、Diosix、Coffer。

文章將要介紹的OpenSBI應用實例采用了FW_JUMP方式的OpenSBI方案。

FW_JUMP類型的固件假設下一個引導階段入口的地址是固定的，例如引導加載程序或操作系統(tǒng)內(nèi)核，而不直接包含下一個階段的二進制代碼。

2、內(nèi)核配置

在內(nèi)核配置上，主要涉及到以下選項，也可以通過倉庫中的hpmicro_hpm6800evk_defconfig來獲取默認的配置。

倉庫中還提供了基礎的GPIO和PINMUX驅動，愛好者們可以通過修改設備樹來實現(xiàn)LED和按鍵功能，而不用修改內(nèi)核驅動代碼。對于其他的外設的PINMUX配置，也可以通過修改設備樹來完成。

3、Loader配置

由于HPM芯片啟動時一般是以XIP的方式執(zhí)行flash中的代碼，所以需要一個loader程序來實現(xiàn)將OpenSBI、kernel、設備樹等固件拷貝到其運行地址中。

除了搬移固件外，loader還需要做一些基礎的初始化工作，包括sdram/ddr的使能，默認console的時鐘和串口的pinmux配置等。

做完這些工作后，loader跳轉至OpenSBI的入口函數(shù)，將系統(tǒng)交給OpenSBI來管理，接著OpenSBI在做完準備工作后，跳轉至內(nèi)核。

4、BuildRoot配置

單獨編譯loader、OpenSBI、Linux內(nèi)核和文件系統(tǒng)并進行燒寫是可行的，但是不是那么的方便，使用BuildRoot，我們可以方便的將這些固件整合到一起，一次性編譯出整個固件。

4.1loader的添加

首先將編寫好loader固件上傳到git服務器上。然后在buildroot的boot目錄下創(chuàng)建一個文件夾hpmicro_loader,在其中添加兩個新文件：Config.in和hpmicro_loader.mk

Config.in中主要是創(chuàng)建了一個Kconfig選項，用來選擇是否要使能hpmicro_loader。使能后hpmicro_loader.mk會被加入到編譯系統(tǒng)中。

在本文的實現(xiàn)中，loader是基于hpm_sdk進行編寫的，其中將hpm_sdk作為submodule引入，所以在hpmicro_loader.mk中，不僅要將loader的倉庫地址填入，還需要指定HPMICRO_LOADER_GIT_SUBMODULES = yes來讓編譯系統(tǒng)去初始化submodule，否則會缺失hpm_sdk文件。同時由于hpm_sdk是基于cmake構建系統(tǒng)的，還需要指定hpmciro_loader的構建系統(tǒng)為cmake：$(eval $(cmake-package))。由于hpm_sdk不支持源文件目錄下直接編譯，所以要指定HPMICRO_LOADER_SUPPORTS_IN_SOURCE_BUILD = no。再指定一些SDK編譯需要的環(huán)境變量后，就可以順利進行編譯了。

編譯結束后，通過后處理命令，將編譯輸出的bin文件，拷貝到genimage的工作目錄，用于最終的鏡像生成。

define HPMICRO_LOADER_INSTALL_TARGET_CMDS
dd if=/dev/zero of=$(@D)/buildroot-build/output/temp.bin bs=1 count=1024
cat $(@D)/buildroot-build/output/temp.bin $(@D)/buildroot-build/output/demo.bin > $(@D)/buildroot-build/output/opensbiloader.bin
$(INSTALL) -D -m 0644 $(@D)/buildroot-build/output/opensbiloader.bin $(BINARIES_DIR)/opensbiloader.bin
endef

4.2 Kernel版本的指定

Kernel的自定義版本指定功能是BuildRoot自帶的，我們可以通過修改以下兩個選項來指定Kernel的版本。

· 指定Kernel版本

BR2_LINUX_KERNEL_CUSTOM_TARBALL=y
BR2_LINUX_KERNEL_CUSTOM_TARBALL_LOCATION="$(call github,hpmicro,linux,7b088c87b6758e413bd316bf883438f7134f1e7f)/linux-7b088c87b6758e413bd316bf883438f7134f1e7f.tar.gz"

其中github,hpmicro,linux代表了倉庫地址為github/hpmicro/linux.git,后邊的7b088c87b6758e413bd316bf883438f7134f1e7f為指定的提交編號

也可以通過menuconfig在圖形界面中去修改。

·指定Kernel的配置文件

BR2_LINUX_KERNEL_DEFCONFIG="nommu_hpmicro"

· 指定設備樹文件

BR2_LINUX_KERNEL_DTS_SUPPORT=y
BR2_LINUX_KERNEL_INTREE_DTS_NAME="hpmicro/hpm6800-evk"

4.3 OpenSBI版本的指定

OpenSBI的版本指定和Kernel的版本指定類似

BR2_TARGET_OPENSBI_CUSTOM_REPO_URL="https://github.com/hpmicro/opensbi.git"
BR2_TARGET_OPENSBI_CUSTOM_REPO_VERSION="2900da09af75c80ed8c4a8553a35e94e0f3f5c0d"
BR2_TARGET_OPENSBI_VERSION="2900da09af75c80ed8c4a8553a35e94e0f3f5c0d"

· 指定OpenSBI的平臺名稱：

BR2_TARGET_OPENSBI_PLAT="hpmicro"

4.4 鏡像排布的指定

采用genimage對各個獨立的鏡像進行整合:創(chuàng)建genimage腳本文件genimage_opensbi.cfg, 指定每個鏡像文件存放的位置:

flash w25q128 {
pebsize = 64K
numpebs = 256
minimum-io-unit-size = 1
}
image flash.img {
flash {
}
flashtype = "w25q128"
partition opensbiloader {
size = 64k
image = "opensbiloader.bin"
}
partition opensbi {
offset = 64K
image = "fw_jump.bin"
size = 192K
}

partition kernel {
image = "Image"
offset = 256K
size = 2880K
}
partition dtb {
image = "hpm6800-evk.dtb"
offset = 3136K
size = 64K
}
partition rootfs {
image = "rootfs.squashfs"
offset = 4M
size = 1M
}
}

5、編譯過程

5.1 OpenSBI單獨編譯：

· Github倉庫地址

https://github.com/hpmicro/opensbi.git

· 編譯命令

make all PLATFORM=hpmicro CROSS_COMPILE=riscv32-unknown-elf- HPMSOC=HPM6800 O={build_dir}

編譯完成后可以在{build_dir}中找到platform/hpmicro/firmware/fw_jump.bin，需要loader將其拷貝到地址0然后再跳轉到地址0來運行。

5.2 Loader參考：

· Github倉庫地址

https://github.com/hpmicro/hpm_opensbi_loader.git

· 編譯命令

HPM_SDK_BASE={SDKBASE} GNURISCV_TOOLCHAIN_PATH={RISCV TOOLCHAIN PATH} HPM_SDK_TOOLCHAIN_VARIANT=gcc cmake -GNinja -DBOARD=hpm6800evk -DHPM_BUILD_TYPE=flash_xip -B build

5.3 buildroot工程編譯：

· Github倉庫地址

https://github.com/hpmicro/buildroot.git

· 編譯命令

make hpmicro_hpm6800evk_defconfig
make all

6、燒錄和運行

· 燒錄需要用到hpm_manufacturing_tool，倉庫地址：

https://github.com/hpmicro/hpm_manufacturing_tool.git

將buildroot生成的鏡像output/images/flash.img重命名成flash.bin燒錄到0x80000000即可。

OpenSBI v0.6
____ _____ ____ _____
/ __ \ / ____| _ \_ _|
| | | |_ __ ___ _ __ | (___ | |_) || |
| | | | '_ \ / _ \ '_ \ \___ \| _ < | |
| |__| | |_) | __/ | | |____) | |_) || |_
\____/| .__/ \___|_| |_|_____/|____/_____|
| |
|_|

Platform Name : HPMicro D45
Platform HART Features : RV32ACDFIMSUX
Platform Max HARTs : 1
Current Hart : 0
Firmware Base : 0x0
Firmware Size : 76 KB
Runtime SBI Version : 0.2

MIDELEG : 0x00000222
MEDELEG : 0x0000b109
PMP0 : 0x00000000-0x0001ffff (A)
PMP1 : 0x01200000-0x0127ffff (A,R,W,X)
PMP2 : 0x40000000-0x41ffffff (A,R,W,X)
PMP3 : 0x80000000-0x9fffffff (A,R,X)
PMP4 : 0xe0000000-0xefffffff (A,R,W)
PMP5 : 0xf0000000-0xffffffff (A,R,W)
[ 0.000000] Linux version 6.10.0 (ubuntu@ubuntu-virtual-machine) (riscv32-buildroot-linux-uclibc-gcc.br_real (Buildroot -g71f87772fd) 13.3.0, GNU ld (GNU Binutils) 2.41) #1 Sat Sep 14 10:38:43 CST 2024
[ 0.000000] Machine model: HPMicro HPM6800 Evaluate Kit
[ 0.000000] SBI specification v0.2 detected
[ 0.000000] SBI implementation ID=0x1 Version=0x6
[ 0.000000] SBI TIME extension detected
[ 0.000000] SBI IPI extension detected
[ 0.000000] SBI RFENCE extension detected
[ 0.000000] earlycon: sbi0 at I/O port 0x0 (options '')
[ 0.000000] printk: legacy bootconsole [sbi0] enabled
[ 0.000000] printk: debug: ignoring loglevel setting.
[ 0.000000] Zone ranges:
[ 0.000000] Normal [mem 0x0000000040000000-0x0000000041ffffff]
[ 0.000000] Movable zone start for each node
[ 0.000000] Early memory node ranges
[ 0.000000] node 0: [mem 0x0000000040000000-0x0000000041ffffff]
[ 0.000000] Initmem setup node 0 [mem 0x0000000040000000-0x0000000041ffffff]
[ 0.000000] riscv: base ISA extensions acdfim
[ 0.000000] riscv: ELF capabilities acdfim
[ 0.000000] pcpu-alloc: s0 r0 d32768 u32768 alloc=1*32768
[ 0.000000] pcpu-alloc: [0] 0
[ 0.000000] Kernel command line: earlycon=sbi console=hvc0 ignore_loglevel rootwait root=/dev/mtdblock0
[ 0.000000] Dentry cache hash table entries: 4096 (order: 2, 16384 bytes, linear)
[ 0.000000] Inode-cache hash table entries: 2048 (order: 1, 8192 bytes, linear)
[ 0.000000] Built 1 zonelists, mobility grouping on. Total pages: 8192
[ 0.000000] mem auto-init: stack:all(zero), heap alloc:off, heap free:off
[ 0.000000] Memory: 30248K/32768K available (1370K kernel code, 298K rwdata, 266K rodata, 97K init, 136K bss, 2520K reserved, 0K cma-reserved)
[ 0.000000] SLUB: HWalign=64, Order=0-3, MinObjects=0, CPUs=1, Nodes=1
[ 0.000000] NR_IRQS: 64, nr_irqs: 64, preallocated irqs: 0
[ 0.000000] riscv-intc: 32 local interrupts mapped
[ 0.000000] clocksource: riscv_clocksource: mask: 0xffffffffffffffff max_cycles: 0x588fe9dc0, max_idle_ns: 440795202592 ns
[ 0.000005] sched_clock: 64 bits at 24MHz, resolution 41ns, wraps every 4398046511097ns
[ 0.008230] Calibrating delay loop (skipped), value calculated using timer frequency.. 48.00 BogoMIPS (lpj=96000)
[ 0.018469] pid_max: default: 4096 minimum: 301
[ 0.023214] Mount-cache hash table entries: 1024 (order: 0, 4096 bytes, linear)
[ 0.030507] Mountpoint-cache hash table entries: 1024 (order: 0, 4096 bytes, linear)
[ 0.041674] devtmpfs: initialized
[ 0.048165] clocksource: jiffies: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 7645041785100000 ns
[ 0.057969] pinctrl core: initialized pinctrl subsystem
[ 0.087311] cpu0: Ratio of byte access time to unaligned word access is 1.65, unaligned accesses are fast
[ 0.098916] platform soc: Fixed dependency cycle(s) with /soc/interrupt-controller@e4000000
[ 0.109020] platform soc: Fixed dependency cycle(s) with /soc/interrupt-controller@e4000000
[ 0.120899] clocksource: Switched to clocksource riscv_clocksource
[ 0.130851] workingset: timestamp_bits=30 max_order=13 bucket_order=0
[ 0.137423] squashfs: version 4.0 (2009/01/31) Phillip Lougher
[ 0.155691] riscv-plic e4000000.interrupt-controller: mapped 76 interrupts with 1 handlers for 2 contexts.
[ 0.167985] hpmicro gpio f00d0000.gpio-controller: port0dx, ngpios32
[ 0.175826] hpmicro gpio f00d0000.gpio-controller: gpio irq_num 1, dev_namef00d0000.gpio-controller
[ 0.185459] hpmicro gpio f00d0000.gpio-controller: port1dx, ngpios32
[ 0.192568] hpmicro gpio f00d0000.gpio-controller: gpio irq_num 2, dev_namef00d0000.gpio-controller
[ 0.202134] hpmicro gpio f00d0000.gpio-controller: port2dx, ngpios32
[ 0.209294] hpmicro gpio f00d0000.gpio-controller: gpio irq_num 3, dev_namef00d0000.gpio-controller
[ 0.218797] hpmicro gpio f00d0000.gpio-controller: port3dx, ngpios32
[ 0.225921] hpmicro gpio f00d0000.gpio-controller: gpio irq_num 4, dev_namef00d0000.gpio-controller
[ 0.235458] hpmicro gpio f00d0000.gpio-controller: port4dx, ngpios32
[ 0.242579] hpmicro gpio f00d0000.gpio-controller: gpio irq_num 6, dev_namef00d0000.gpio-controller
[ 0.252514] hpmicro gpio f00d0000.gpio-controller: port5dx, ngpios32
[ 0.259651] hpmicro gpio f00d0000.gpio-controller: gpio irq_num 7, dev_namef00d0000.gpio-controller
[ 0.271904] printk: legacy console [hvc0] enabled
[ 0.271904] printk: legacy console [hvc0] enabled
[ 0.281387] printk: legacy bootconsole [sbi0] disabled
[ 0.281387] printk: legacy bootconsole [sbi0] disabled
[ 0.291843] Serial: 8250/16550 driver, 4 ports, IRQ sharing disabled
[ 0.304084] f0040000.uart0: ttyS0 at MMIO 0xf0040000 (irq = 8, base_baud = 1500000) is a 16550A
[ 0.313704] hpmicro-uart f0040000.uart0: hpm-uart probe success
[ 0.322184] hpmicro-uart f004c000.uart3: hpm-uart probe success
[ 0.328959] physmap-flash 80400000.rom: physmap platform flash device: [mem 0x80400000-0x80ffffff]
[ 0.340420] pinctrl-hpmicro f4040000.pinctrl: pin167 config set:
[ 0.346446] pinctrl-hpmicro f4040000.pinctrl: 5:1
[ 0.351353] pinctrl-hpmicro f4040000.pinctrl: 14:1
[ 0.356376] pinctrl-hpmicro f4040000.pinctrl: 128:3
[ 0.361505] pinctrl-hpmicro f4040000.pinctrl: 129:0
[ 0.367076] input: gpio-keys0 as /devices/platform/gpio-keys0/input/input0
[ 0.374457] evbug: Event. Dev: input0, Type: 1, Code: 304, Value: -1
[ 0.380747] evbug: Event. Dev: input0, Type: 0, Code: 0, Value: 0
[ 0.386999] evbug: Connected device: input0 (gpio-keys0 at gpio-keys-polled/input0)
[ 0.394686] evbug: Event. Dev: input0, Type: 1, Code: 304, Value: 0
[ 0.400939] evbug: Event. Dev: input0, Type: 0, Code: 0, Value: 0
[ 0.410306] ledtrig-cpu: registered to indicate activity on CPUs
[ 0.425354] pinctrl-hpmicro f4040000.pinctrl: pin166 config set:
[ 0.431358] pinctrl-hpmicro f4040000.pinctrl: 5:1
[ 0.436289] pinctrl-hpmicro f4040000.pinctrl: 14:1
[ 0.441351] pinctrl-hpmicro f4040000.pinctrl: 128:3
[ 0.446424] pinctrl-hpmicro f4040000.pinctrl: 129:0
[ 0.452175] input: gpio-keys1 as /devices/platform/gpio-keys1/input/input1
[ 0.459436] evbug: Connected device: input1 (gpio-keys1 at gpio-keys/input0)
[ 0.466928] clk: Disabling unused clocks
[ 0.471437] cramfs: checking physical address 0x80400000 for linear cramfs image
[ 0.480081] VFS: Mounted root (squashfs filesystem) readonly on device 31:0.
[ 0.487534] devtmpfs: mounted
[ 0.490877] Freeing unused kernel image (initmem) memory: 96K
[ 0.496618] This architecture does not have kernel memory protection.
[ 0.503115] Run /sbin/init as init process
[ 0.507258] with arguments:
[ 0.510291] /sbin/init
[ 0.513096] with environment:
[ 0.516231] HOME=/
[ 0.518701] TERM=linux
[ 1.553000] random: crng init done
mount: mounting devpts on /dev/pts failed: No such device
sh: can't execute 'seedrng': No such file or directory

Welcome to Buildroot
buildroot login:

當按下開發(fā)板上的按鍵時，會有信息打印出來：

[ 3.208963] evbug: Event. Dev: input0, Type: 1, Code: 304, Value: 1
[ 3.215174] evbug: Event. Dev: input0, Type: 0, Code: 0, Value: 0
[ 3.388948] evbug: Event. Dev: input0, Type: 1, Code: 304, Value: 0
[ 3.395153] evbug: Event. Dev: input0, Type: 0, Code: 0, Value: 0
[ 3.808915] evbug: Event. Dev: input1, Type: 1, Code: 305, Value: 1
[ 3.815120] evbug: Event. Dev: input1, Type: 0, Code: 0, Value: 0
[ 3.952914] evbug: Event. Dev: input1, Type: 1, Code: 305, Value: 0
[ 3.959119] evbug: Event. Dev: input1, Type: 0, Code: 0, Value: 0
[ 4.284913] evbug: Event. Dev: input1, Type: 1, Code: 305, Value: 1
[ 4.291118] evbug: Event. Dev: input1, Type: 0, Code: 0, Value: 0
[ 4.420915] evbug: Event. Dev: input1, Type: 1, Code: 305, Value: 0
[ 4.427115] evbug: Event. Dev: input1, Type: 0, Code: 0, Value: 0