Transcript Water - Meetup

Linux Device Drivers
Prithvi N. Rao
January 12th, 2012
Agenda
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Overview of Linux Device Driver Architecture (Desktop)
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Overview of Linux Device Driver Architecture (Android)
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Device Driver Development Checklist
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How much do you really need to know about Hardware?
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Writing a Linux/Android Device Driver – Getting Started
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Debugging a Linux Device Driver in Android
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Driver Event propagation to the Android Application
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Accessing Events from Android User Space
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Using CCSv5 for debugging Linux kernel in Android
!Agenda
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Dinner – You're on your own :-)!
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History of Linux
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Details of how Linux works
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Android Tutorial
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How to Build Linux kernel for Android
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How to create a NAND flash image
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Shrink Wrapped Driver Development Kit !
Acknowledgements
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Oleg Perelet
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Tom Olson
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Jeff Janis
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Roger Yang
Overview of Linux Device Driver
Architecture (Desktop)
Overview of Linux Device Driver
Architecture (Android)
Overview of Linux Device Driver
Architecture (Android)
Device Driver Development Checklist
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Machine Running Linux or Equivalent with sources installed (Git)
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EVM for Development, RS232 Cable, USB Cable for EVM
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JTAG Emulator/Trace 32 Lauterbach
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Hardware Reference manuals
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Board (Mistral AM/DM37x OMAP 3730 TRM)
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Device (Avago ADBS-A350 Optical Finger Navigation Data Sheet)
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Code Composer Studio version 5
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Putty (for Unix connectivity)
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SD Card and reader/writer
How Much Do You Really Need to Know
About Hardware?
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The more you know the better
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Be nice to the hardware chaps...you will need them :-)!
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Bringing food and other goodies helps (Android Tablets, Android Phones)
Seriously you need to spend some time understanding
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How the device is hooked up to the EVM
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How to read a schematic
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How interrupts work (edge triggered, level triggered)
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How to use an oscilloscope
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How to convince the hardware chaps that it is their problem :-)!
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I2C Protocol and SMBUS
MOST OF ALL DON'T BE INTIMIDTED BY HARDWARE
Writing a Linux Device Driver
TIME TO GET REAL
Optical Finger Navigation Driver
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First determine what is the purpose of this device
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Input Only (in our case for OFN)
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Output Only
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Both
Decide where in the kernel sources it should reside
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kernel/drivers/input/mouse/avagoADBMA350.c
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kernel/drivers/input/mouse/avagoADBMA350.h
Edit the Kconfig and Makefile
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Each directory in “drivers” has a Kconfig and Makefile
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Enter the details of the driver code in here
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Top level kernel build picks all this up and handles the build
Optical Finger Navigation Driver
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Draw a block diagram of the hardware and control and data flows
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K3-K4->Deliverables->K3-OpticalTouchPad
Follow the “guidelines” on how to write in-kernel device drivers
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Look at ”safari books on line”
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Use Google
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kernel/Documentation has lots of stuff but requires filtering
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Look at other in-kernel drivers in Linux - REALLY!
!PANIC
Debugging a Linux Device Driver
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Panicking can be good
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If it is in the kernel – you know where the PC is
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printk can get you a long way
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U-boot is very useful but requires some work
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Debugfs is absolutely a must (in my opinion)
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.config in kernel directory allows you to output various kernel driver messages
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Look for #interrupts in /proc/interrupts
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Look for events in /dev/input/eventX (from your device)
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CCSv5 is useful for kernel debug in general
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Talk to me if you want to know how to do this
Driver Event Propagation in Linux/Android
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Linux exposes externally a uniform input event interface for each device
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/dev/input/eventX
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Each device driver has to register/unregister itself
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Each device driver publishes input events that it receives
Sequence of events for device driver in the kernel
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Probe detects if the device is connected
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input-register-device invoked if device found
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request_irq is used to associate a handler with interrupt
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set up work_queue inside handler (linux version dependent)
It's more fun to look at code :-)!
Driver Event Propagation in Linux/Android
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On receiving an interrupt (user pressed touchpad or moved it)
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IRQ handler is invoked
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Schedule work to propagate event to Android Framework
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input_report_rel
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input_sync
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input_report_key
Android Framework provides a JNI interface to the upper layers.
Accessing Events from Android User
Space
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Android GUI initiates access to events
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Instance of WindowManagerService.java is created
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Utilize MotionEvent.java, InputDevice.java,
InputEvent.java,InputQueue.java, EventHub.java
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Android FrameWork intercepts events and provides a way to access
event queues (/dev/input/eventX)
Overview of Linux Device Driver
Architecture (Android)
Key Take Aways
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Writing a Linux Device Driver is one of the most rewarding experiences
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Don't be intimidated – it's only kernel programming :-)!
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Respect the fact that you ARE working with a serious OS kernel
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The driver must play well with the rest of the system
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Linux has made it simpler than Unix
Understand the hardware as much as you can.
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Share information with the hardware folks
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You will do so eventually...trust me :-)!
Don't blind side them at the last minute with tons of debug info
Be aware that driver architecture has changed in Linux over time
ACCEPT THE CHALLENGE – YOU WON'T REGRET IT!