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Allwinner Kernel Upstreaming Experiences

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Allwinner Kernel Upstreaming Experiences

  1. 1. Allwinner Kernel Upstreaming Experiences Chen-Yu Tsai (wens) 蔡鎮宇
  2. 2. Chen-Yu Tsai 蔡鎮宇 • Software Engineer @ CloudMosa • Puffin Web Browser • Totally not embedded Linux related • Linux-sunxi community hobbyist • Contributions to U-boot and Linux • git log --oneline --author “Chen-Yu Tsai” • Translations 2015/8/25 2
  3. 3. Disclaimer I have only done Allwinner/sunxi related stuff. Linux-sunxi is community/volunteer based. Your mileage may vary. 2015/8/25 3
  4. 4. Outline • Current Status • Where to start • Tips • What to expect • New SoC bringup • Supporting new boards • Priorities • Difficulties 2015/8/25 4
  5. 5. Current Status Let’s look at some ARM SoC vendors 2015/8/25 5
  6. 6. linux-sunxi? • Cheap hardware • Development boards • Documents and SDKs available • Given by hardware vendors • Allwinner now provides them on github • https://github.com/allwinner-zh/ 2015/8/25 6
  7. 7. Allwinner • Headless server w/ MMC/SATA/USB storage • I2C & SPI • LCD/HDMI/VGA display w/ simplefb • Audio WIP 2015/8/25 7
  8. 8. Allwinner • Community driven • git lo --no-merges --perl-regexp --grep 'sunxi|sun[0-9]i' | grep -v m68k | wc –l • 1118 • Extremely active • Allwinner supplies documents and their source code • Answers questions 2015/8/25 8
  9. 9. Rockchip • Basically a fully working system • MMC/USB • I2C & SPI • Full KMS display support • I2S & audio codecs • Chromebook based on mainline kernel + dts • IP blocks mostly from ARM or Synopsys 2015/8/25 9
  10. 10. Rockchip • Hobbyist maintainer • git lo --author 'Heiko Stuebner' | wc -l • 158 • filtered out Samsung related • Official support • git lo --author @rock-chips.com | wc -l • 169 2015/8/25 10
  11. 11. Mediatek • Basics (machine, clk, pinctrl , uart) • Drivers for • I2C, SPI, MMC, PMIC, Audio • Not seen in DTS yet 2015/8/25 11
  12. 12. Mediatek • Outside maintainer • git lo --author 'Matthias Brugger' | wc -l • 53 • Since 2014/7/22 • Official support • git lo --author @mediatek.com | wc -l • 122 • Since 2014/11/4 2015/8/25 12
  13. 13. Where to start 2015/8/25 13
  14. 14. Getting it to boot • Machine definition (arch/arm/mach-*) • Basic DTS • UART 2015/8/25 14
  15. 15. Infrastructure • Clocks • Pinctrl • Reusable 2015/8/25 15
  16. 16. Peripherals • Storage • MMC • SATA • USB • PMIC • I2C • SPI • … • Common vs custom IP? 2015/8/25 16
  17. 17. Tips The kernel is very big and moves very fast 2015/8/25 17
  18. 18. Start small • Is it a known, supported IP block? • Only standard resources? • MMIO, IRQ, clocks, resets • Ex: USB host • Hardware glue? Quirks? • Is the core supported? • Is it a library? • Write a glue driver • Modify / port • Ex: SATA AHCI, STMMAC 2015/8/25 18
  19. 19. Start simple • Clocks can be done one at a time • Driver describes clock controls • Driver or DTS describes relationship between clocks • Both methods are used • Pinctrl / GPIO • Transcribe datasheets 2015/8/25 19
  20. 20. Look around and Ask • Subscribe to mailing lists • Look at how other contributors write code • Learn what reviewers ask for • Look at how other platforms do it • mediatek pinctrl driver is very similar to sunxi • Documentation is sometimes lacking • When in doubt, ask • Release often • No one is going to review unsent code 2015/8/25 20
  21. 21. What to expect Not getting merged is not the end of the world 2015/8/25 21
  22. 22. Code issues • Code style • Indentation • Comments • Error path • Bugs • Resource leak? 2015/8/25 22
  23. 23. NACK • Wrong design • Ex: rfkill dt support • Deprecated functions • Ex: platform_data • Occasional disagreement • “simplefb: add clock handling code” 2015/8/25 23
  24. 24. Maintainers are busy • Sometimes you don’t get feedback • Maintainers often write code as well • Lots of mailing list traffic • Ping or resend 2015/8/25 24
  25. 25. Didn’t get your patches in this release? • You can do better • Write better code • Respond to reviewers • Keep working • Release cycle is predictable • Sometimes it’s not your fault • Maintainer missed your patch or pull request • It happens • Maintainer went on vacation • Maintainer missing (?) 2015/8/25 25
  26. 26. New SoC bringup 2015/8/25 26
  27. 27. New SoC 1. Getting it to Boot • Machine definition (arch/arm/mach-*) • Basic DTS • UART 2. Clocks / Pinctrl 3. Peripherals • IP blocks don’t often change • Existing drivers should work • Quite satisfying! 2015/8/25 27
  28. 28. Supporting new boards 2015/8/25 28
  29. 29. Supporting new boards • Need schematics or hardware description • What peripherals are connected to the board? • What external ICs are there? • PMICs, audio codecs, sensors, storage… • Extra GPIOs? • LEDs • Write a .dts file • Test that everything works • Fairly easy! 2015/8/25 29
  30. 30. Priorities 2015/8/25 30
  31. 31. Paid work • Not really much say • Getting products shipped is all that matters • Still • You should try • What benefits the most platforms / boards? • Must have vs. want? • MMC vs USB vs audio 2015/8/25 31
  32. 32. Community hackers • Expertise / prior experience • Did clocks before, do it again • Interest • Me: I want WiFi! I want SMP! • Low hanging fruit • Me: Network is DWMAC based, only need glue code • Popular demand • DMA engine • Audio 2015/8/25 32
  33. 33. Difficulties 2015/8/25 33
  34. 34. Documents • NDA? • Incorrect • How do you know it’s incorrect? • Missing sections • Completely non-existent • No board schematics • Should you risk it going up in smoke? 2015/8/25 34
  35. 35. Porting vendor code • Is often bad • Because of time to market concerns • Quite old • Android kernel still at 3.4? • Custom frameworks • Obsoleted by common frameworks • Clocks, resets, pinctrl, gpio, PHY, regmap, … • Binary blobs • No source code 2015/8/25 35
  36. 36. Binary drivers • Third-party IP vendors • GPUs • VPUs • … • NDAs 2015/8/25 36
  37. 37. GPL violations • There shouldn’t be binary-only blobs in the kernel • http://linux-sunxi.org/GPL_Violations • http://www.xda-developers.com/have-you-paid- your-linux-kernel-source-license-fee/ 2015/8/25 37
  38. 38. Questions? 2015/8/25 38

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