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Linux Device Drivers

Linux Device Drivers. Prithvi N. Rao January 12 th , 2012. Agenda. Overview of Linux Device Driver Architecture (Desktop) Overview of Linux Device Driver Architecture (Android) Device Driver Development Checklist How much do you really need to know about Hardware?

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Linux Device Drivers

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  1. Linux Device Drivers Prithvi N. Rao January 12th, 2012

  2. Agenda Overview of Linux Device Driver Architecture (Desktop) Overview of Linux Device Driver Architecture (Android) Device Driver Development Checklist How much do you really need to know about Hardware? Writing a Linux/Android Device Driver – Getting Started Debugging a Linux Device Driver in Android Driver Event propagation to the Android Application Accessing Events from Android User Space Using CCSv5 for debugging Linux kernel in Android

  3. !Agenda Dinner – You're on your own :-)! History of Linux Details of how Linux works Android Tutorial How to Build Linux kernel for Android How to create a NAND flash image Shrink Wrapped Driver Development Kit !

  4. Acknowledgements Oleg Perelet Tom Olson Jeff Janis Roger Yang

  5. Overview of Linux Device Driver Architecture (Desktop)

  6. Overview of Linux Device Driver Architecture (Android)

  7. Overview of Linux Device Driver Architecture (Android)

  8. Device Driver Development Checklist Machine Running Linux or Equivalent with sources installed (Git) EVM for Development, RS232 Cable, USB Cable for EVM JTAG Emulator/Trace 32 Lauterbach Hardware Reference manuals Board (Mistral AM/DM37x OMAP 3730 TRM) Device (Avago ADBS-A350 Optical Finger Navigation Data Sheet) Code Composer Studio version 5 Putty (for Unix connectivity) SD Card and reader/writer

  9. How Much Do You Really Need to Know About Hardware? The more you know the better Be nice to the hardware chaps...you will need them :-)! Bringing food and other goodies helps (Android Tablets, Android Phones) Seriously you need to spend some time understanding How the device is hooked up to the EVM How to read a schematic How interrupts work (edge triggered, level triggered) How to use an oscilloscope How to convince the hardware chaps that it is their problem :-)! I2C Protocol and SMBUS MOST OF ALL DON'T BE INTIMIDTED BY HARDWARE

  10. Writing a Linux Device Driver TIME TO GET REAL

  11. Optical Finger Navigation Driver First determine what is the purpose of this device Input Only (in our case for OFN) Output Only Both Decide where in the kernel sources it should reside kernel/drivers/input/mouse/avagoADBMA350.c kernel/drivers/input/mouse/avagoADBMA350.h Edit the Kconfig and Makefile Each directory in “drivers” has a Kconfig and Makefile Enter the details of the driver code in here Top level kernel build picks all this up and handles the build

  12. Optical Finger Navigation Driver Draw a block diagram of the hardware and control and data flows K3-K4->Deliverables->K3-OpticalTouchPad Follow the “guidelines” on how to write in-kernel device drivers Look at ”safari books on line” Use Google kernel/Documentationhas lots of stuff but requires filtering Look at other in-kernel drivers in Linux - REALLY! !PANIC

  13. Debugging a Linux Device Driver Panicking can be good If it is in the kernel – you know where the PC is printk can get you a long way U-boot is very useful but requires some work Debugfs is absolutely a must (in my opinion) .config in kernel directory allows you to output various kernel driver messages Look for #interrupts in /proc/interrupts Look for events in /dev/input/eventX (from your device) CCSv5 is useful for kernel debug in general Talk to me if you want to know how to do this

  14. Driver Event Propagation in Linux/Android Linux exposes externally a uniform input event interface for each device /dev/input/eventX Each device driver has to register/unregister itself Each device driver publishes input events that it receives Sequence of events for device driver in the kernel Probe detects if the device is connected input-register-device invoked if device found request_irq is used to associate a handler with interrupt set up work_queue inside handler (linux version dependent) It's more fun to look at code :-)!

  15. Driver Event Propagation in Linux/Android On receiving an interrupt (user pressed touchpad or moved it) IRQ handler is invoked Schedule work to propagate event to Android Framework input_report_rel input_sync input_report_key Android Framework provides a JNI interface to the upper layers.

  16. Accessing Events from Android User Space Android GUI initiates access to events Instance of WindowManagerService.java is created Utilize MotionEvent.java, InputDevice.java, InputEvent.java,InputQueue.java, EventHub.java Android FrameWork intercepts events and provides a way to access event queues (/dev/input/eventX)

  17. Overview of Linux Device Driver Architecture (Android)

  18. Key Take Aways Writing a Linux Device Driver is one of the most rewarding experiences Don't be intimidated – it's only kernel programming :-)! Respect the fact that you ARE working with a serious OS kernel The driver must play well with the rest of the system Linux has made it simpler than Unix Understand the hardware as much as you can. You will do so eventually...trust me :-)! Share information with the hardware folks 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!

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