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Pushing The Limits Of
Linux On ARM
LinuxCon Japan 2015
Andreas Färber
[email protected]
Overview
2
•
Definition of “Linux on ARM”
•
Transitioning from Embedded to Servers & Desktops
•
Pushing the limits
‒
in general
‒
for embedded
Linux On ARM
Quick Introduction
•
•
•
Architecture by ARM Ltd. / ARM Holdings plc (UK)
‒
ARM7, ARM9 used in embedded devices “for ages”
‒
ARMv7 with Cortex-A8, etc. also popular with hobbyists
‒
ARMv8 offers 64-bit AArch64 mode, attractive for servers
Development boards (for ARMv7) abundant
‒
Reminder: Android is based on the Linux kernel, but
‒
Too often unofficial “downstream” kernel forks are used
Goal: Get support for ARM boards into the official
kernel.org Linux tree (“mainline” or “upstream”)
‒
4
To run a standard userspace distribution, e.g. openSUSE
From Embedded And Mobile
To Desktop And Servers
From Embedded To Desktop & Servers
•
•
Traditionally used in resource-constrained devices
‒
Cross-built with configuration optimized for target device
‒
Device drivers built into kernel (e.g., exynos_defconfig)
Multi-platform support allows to build support for
multiple chip platforms into a single kernel
‒
‒
6
Allows for generic kernel with most drivers as modules
‒
Less tested, some build failures caught via randconfig
‒
Occasional runtime failures only found when testing on device!
Requires such devices to be supported by one kernel source
The openSUSE Kernel
linux.git
linux-stable.git
openSUSE:Factory:ARM
openSUSE:Factory
kernel.git
Kernel:stable
kernel-source.git
Kernel:HEAD
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Pushing The Limits
Where Are Limits Being Pushed?
•
New ARM IP
‒
•
New chip vendors
‒
•
Handled by ARM themselves (except for Mali graphics)
Linaro can help ARM licensees get started properly
New chips, new boards
‒
Vendors often distribute a Board Support Package (BSP)
including Linux kernel but don't submit their patches
‒
•
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Little or no security fixes, no new upstream features
Old chips and boards people didn't need Linux on yet
Simplest: Board Support
•
Prereq.: SoC (platform and drivers) supported
•
Device Tree (.dts) is used as hardware description
‒
•
ACPI upcoming as alternative hardware description
‒
•
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Either supplied to firmware (U-Boot), or by firmware (UEFI)
Supplied by firmware (UEFI)
No .dts file for your board? Then add it yourself!
‒
Peek at downstream .dts and/or similar upstream .dts files
‒
Read schematics, if available; fallback: trial-and-error
‒
Examples: exynos5250-spring.dts, zynq-parallella.dts
Advanced: System-On-Chip Support
•
Prereq.: SoC family already supported
•
.dtsi file will reference at least one new driver
•
Technical Reference Manual or vendor tree needed
•
11
‒
Compare chip-specific bits to those of one already supported
‒
Peek at earlier and later .dtsi files and drivers? (Careful!)
Example: Samsung Exynos 5410
Expert: New System-on-Chip Support
•
Prereq.: CPU architecture already supported (ARM)
•
Technical Reference Manual really needed
•
12
‒
Serial console driver – to get output
‒
Clocksource driver(s) – for timers
‒
Clock driver
‒
Reset driver?
‒
Memory controller?
Example: STM32 F4
“Some things have to be done
just because they are possible.
Not because they make sense.”
- SUSE Hackweek T-Shirt
13
The Final Frontier (1/2)
Cortex-A72
Cortex-A57
Cortex-A17
Cortex-A53
Cortex-A9
Cortex-A8
ARM11
ARM9
ARM7
Cortex-A12
Cortex-A7
Cortex-A5
OMAP3xxx
BCM2835
…
14
Cortex-A15
…
The Final Frontier (2/2)
Cortex-M7
Cortex-M4
Cortex-M3
Cortex-M1
Cortex-M0
EFM32 GG
LPC18xx
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Cortex-M0+
STM32 F4
STM32 F429 – Flash Layout
Address
Size
08000000
16 KB
Bootloader
08004000
16 KB
Device Tree
08008000
16 KB
Kernel
0800c000
16 KB
08010000
64 KB
08020000
128 KB
08040000
128 KB
08060000
128 KB
08080000
128 KB
080a0000
128 KB
080c0000
128 KB
080e0000
128 KB
08100000
16 KB
08104000
16 KB
08108000
16 KB
0810c000
16 KB
08110000
64 KB
08120000
128 KB
08140000
128 KB
...
16
...
Usage
•
Custom bootloader (1.6 / 16 KB)
‒
github.com/afaerber/afboot-stm32
‒
Compare: U-Boot ~75 KB / 128 KB
•
Device Tree (2.9 / 16 KB)
•
Kernel (1235.5 / 1248 KB)
‒
Execute-in-place (XIP) image
‒
Me: clk, clocksource, serial, fbdev
‒
Maxime: clocksource, reset, serial, pinc.
‒
Root filesystem
•
Daniel: clk
romfs (293.1 / 768 KB)
Bootloader tasks on ARMv7-M
•
Usually runs from flash, using SRAM
•
Initializes clocks
•
Configures pins
•
Sets up serial port (for debug output)
•
Sets up memory controller for SDRAM or PSRAM
•
If necessary, takes timers out of reset
•
Jumps to the kernel entry point
‒
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Start of xipImage plus 1 for THUMB mode
Summary
•
ARMv7-A chips usually well supported these days
‒
But boards not always!
•
ARMv7-M chips often not supported by vendors
•
What ARMv7-M boards may be able to run Linux:
‒
4+ MB of SDRAM/PSRAM
‒
‒
1+ MB of flash
‒
‒
Memory-mapped flash allows execution in place, saves RAM
Secondary storage needed?
‒
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Chip needs some external memory interface to enable it
SPI, MMC, network, …
One More Thing …
Spansion FM4 – Status
Address
Size
Usage
00000000
8 KB
Bootloader
00002000
8 KB
Device Tree
00004000
8 KB
Kernel
•
‒
8 KB
32 KB
64 KB
•
64 KB
64 KB
64 KB
64 KB
Device Tree (0.8 / 8 KB)
•
Kernel (1070 / 2032 KB)
64 KB
‒
64 KB
64 KB
64 KB
64 KB
64 KB
8 KB
...
20
...
github.com/afaerber/afboot-fm4
•
64 KB
64 KB
But no working flash driver yet
Custom bootloader (1.5 / 8 KB)
‒
64 KB
64 KB
OpenOCD 0.9.0
•
clocksource (WIP)
2 MB of on-chip flash available
Infineon XMC4500 – Status
Address
Size
Usage
0c000000
16 KB
Bootloader
0c004000
16 KB
Device Tree
0c008000
•
OpenOCD 0.9.0
‒
Kernel
•
Custom bootloader (2.4 / 16 KB)
‒
github.com/afaerber/afboot-xmc4000
•
Device Tree (3.7 / 16 KB)
•
Kernel (~986.6 / 992 KB)
‒
•
21
Flash driver by Jeff Ciesielsky
clk, clocksource, reset, pinctrl, serial,
sdhci drivers
1 MB of on-chip flash available only
Questions?
Join us on #opensuse-arm or
[email protected]!
en.opensuse.org/Portal:ARM
Thank you.
Have a Lot of Fun, and Join Us At:
www.opensuse.org
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Richard Brown
[email protected]
Design & Inspiration
openSUSE Design Team
http://opensuse.github.io/brandingguidelines/