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https://www.pengutronix.de
2/18
About me
Member of Pengutronix graphics and kernel team
Low-level infrastructure guy
On this Rock I will build my System Why Open-Source Firmware matters - - PowerPoint PPT Presentation
On this Rock I will build my System Why Open-Source Firmware matters - - PowerPoint PPT Presentation
On this Rock I will build my System Why Open-Source Firmware matters Lucas Stach l.stach@pengutronix.de https://www.pengutronix.de About me Member of Pengutronix graphics and kernel team Low-level infrastructure guy Working on
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SLIDE 3
3/18
Where do we come from?
Minimalistic Firmware
Even got used to call them „bootloaders“
Usually no run-time interaction with kernel
SLIDE 4
4/18
Old model – the good
Full control over system operation in Linux kernel
Helps when debugging complex interactions
Easy update story
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5/18
Old model – the bad
High complexity in Linux kernel
As bad as it sounds? Likely not…
Some features hard to implement in a generic kernel
Things start to look difgerent when virtualization is added
SLIDE 6
6/18
Enter PSCI
Power State Coordination Interface
Moves system global and CPU power state into abstract interface
Trap based (like syscall)
Bare-metal and virtualized kernel see same thing
SLIDE 7
7/18
Enter PSCI
VM Kernel Bare-metal Kernel (KVM) Secure Monitor Firmware SMC (trapped) SMC
SLIDE 8
8/18
Trusted Firmware
Help vendors in implementing PSCI and other basic platform functions in a standard compliant way
Started by ARM, now a Linaro project
BSD licensed
SLIDE 9
9/18
PSCI – collision with reality
Real-world Hardware struggles: shared Registers
CPU0 power control CPU1 power control Device0 power control Device1 power control ...
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10/18
PSCI – collision with reality
Real-world Hardware struggles: shared Interfaces
SoC PMIC VDDx VDDy I2C
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11/18
PSCI – collision with reality
Lots of hardware not designed to provide the separation required by PSCI
May not even be possible entirely
SLIDE 12
12/18
Down the rabbit hole: SCMI
System Control and Management Interface
Move lots more functionality to SCMI provider
Device power/performance states
Clocks
Sensors
System control
SLIDE 13
13/18
Down the rabbit hole: SCMI
Linux kernel implementation gets easy
Firmware get much more complex
Lots of runtime interactions between OS and FW
Sometimes hard to reason about
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14/18
Complex Firmware
Can I decide to just don‘t care? Maybe...
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15/18
Complex Firmware
Can I decide to just don‘t care? Probably not!
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16/18
Asymetric SoCs
Application Processor Minion Core RT Core Shared System Resources
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17/18
Asymetric SoCs
Application Processor Minion Core RT Core Clock UART SPI System Control Processor
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18/18
T akeaways
Firmware taking over more functionality is here to stay
Incentive for chip vendors to open-source not as high as with Linux kernel