Abstract Francois Tigeot has been trying to make DragonFly more useful by improving its performance, making it able to use some common technologies such as PAM/NSS and porting various pieces of software. One of these pieces of software was the new kms infrastructure and its associated drm/i915 driver. The talk about how it has been ported from FreeBSD, the difficulties with making it first run on DragonFly and its evolution from there. Speaker bio François Tigeot is an Independent consultant, sysadmin, XFree86/Xorg user since 1996, BSD user since 1999 and DragonFly developer since 2011

1. 1/28
Porting DRM/KMS drivers to DragonFly BSD
François Tigeot
<ftigeot@wolfpond.org>

2. 2/28
About myself
● Consultant, software developer, Sysadmin
● Former ccTLD System Engineer
● X11 and *BSD user since a heck of a long time
● Introduced FreeBSD in the .fr registry
● DragonFly developer since 2011

3. 3/28
About DragonFly
● Unix-like Operating System
● Forked from FreeBSD 4.8 in 2003 by Matthew
Dillon
● Aims to be high-performance and scalable
● Uses per-core replicated resources
● Many operations are naturally lockless
● Caches stay hot

4. 4/28
About DragonFly (2)
● Innovative features very useful for some workloads
● HAMMER filesystem
– History retention
– Deduplication
– Real-time replication
● Swapcache: second-level file cache
– Uses existing swap infrastructure
– Optimized for SSDs

5. 5/28
About DragonFly (3)
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PostgreSQL 9.3 performance
DragonFly 3.6.1
Debian 7.0
Centos 6.5
Clients
TPS

6. 6/28
First tentative
● David Shao, Google Summer Of Code 2010
● Based on Linux + a compatibility layer
● Dropped early but continued in his spare time
later
● Apparently got something to work
● Sadly probably specific to his machine
● Only got crashes with my hardware

7. 7/28
Starting again with FreeBSD
● Many common kernel APIs with DragonFly, seemed
like a good idea at the time
● June 2012: Start implementing newly required APIs
● December 2012: drm/i915 mostly ported
● June 2013: i915 starts working after adding PAT
support to the kernel
● October 2013: ttm + radeon mostly ported
● July 2014: ttm + radeon working reliably

8. 8/28
FreeBSD dropped the ball
● No significant updates to drm/i915 after 2012
● Latest supported hardware: Ivy-Bridge
● Prevents updates to their generic drm code and
the drm/radeon driver
● I switched to Linux as the new i915 upstream in
September 2013
● Most important goal: Haswell support

9. 9/28
FreeBSD issues
● FreeBSD code vastly different from Linux
● Some very old parts
● Most modern features ~= Linux 3.4
● Two different versions of drm + drm drivers
– Old drm/ directory
– New drm2/ directory
● Most code the same, pointlessly duplicated!

10. 10/28
Rebasing on Linux (1)
● Target: Linux 3.8.13
● Linux 3.8 first version with known working
Haswell support
● drm/radeon port based on Linux 3.8
● OpenBSD also targeting Linux 3.8.x
● OpenBSD has the best *BSD drm
implementation so far (2014-09)

11. 11/28
Rebasing on Linux (2)
● Remove FreeBSD-inherited drm2/ directory
● Put everything into drm/
● Remove old drm1 radeon and i915 drivers in
the process
● Also clean up the agp driver

12. 12/28
Update process
● 1. Diff Linux and DragonFly code
● 2. Reduce pointless noise
● 3. Identify important functional differences
● 4. Implement them piecemeal
● 6. Replay Linux git history if required
● 5. Try to keep commits small

13. 13/28
Pointless noise in drm/i915
● Different file names
● Functions implemented in different order
● Functions present in different files
● Two previous items biggest source of loc
differences
● June 2014: moved most functions to the same
place they were in Linux 3.8.13
● Reduced differences from ~= 50K to 22K loc

14. 14/28
Style changes in drm/i915
● The FreeBSD drm/i915 author basically rewrote
the entire driver to change its coding style
– if (ret != 0)
– If (ret)
● It was unmaintainable
● Had to reduce the amount of noise before
tackling functional differences

15. 15/28
Difficult spots
● GEM VM code
– FreeBSD used custom do-everything routines different
from the Linux GEM implementation
– i915_gem_obj_io() in FreeBSD
– Various functions like i915_gem_shmem_pwrite() in
Linux
● I2c API in Linux, iic API in FreeBSD+DragonFly
● Hard to make these parts of the drivers work like
they do in Linux

16. 16/28
Implement Linux APIs
● Same old idea as David Shao's who used a
Linux compatibility layer
● Many linux/xxx.h wrappers taken from FreeBSD
(OFED project, Infiniband)
● Some APIs implemented locally: idr(9), various
linux/yyy.h headers, etc...
● Other Linux functions taken from OpenBSD

17. 17/28
Implement Linux APIs (2)
● Graphic drivers very complex
● Fast moving targets
● It makes more sense to change the DragonFly
kernel to behave like Linux than trying to
constantly keep up and change the drivers to
use *BSD-specific APIs
● In a way I'm porting DragonFly to the drm
drivers and not the drivers to DragonFly

18. 18/28
Implement Linux APIs (3)
● ls /usr/src/sys/drm/include/linux
atomic.h export.h jiffies.h timer.h
bitops.h hash.h kernel.h types.h
compiler.h highmem.h kref.h wait.h
completion.h i2c.h list.h workqueue.h
delay.h idr.h mutex.h
err.h io.h time.h
● Most common Linux APIs used in i915 ttm and radeon
implemented by wrappers
● Reduce differences as much as possible in the drm/* directories
● Major exception: locking directives

19. 19/28
The road to Haswell support
● 1. Reduce noise
● 2. Replace FreeBSD APIs by Linux ones
● 3. Update the interrupt code
● 4. Update the ringbuffer code
● 5. Update the output management code
● 6. Haswell-specific cache attributes in page tables
● Finally working reliably in August 2014

20. 20/28
A few words about Userland
● Pkgsrc packages used until 2013
● Xorg-server 1.6
● I wanted to update it
● Didn't happen
● Lost interest

21. 21/28
A few words about Userland (2)
● Switched to Dports
● FreeBSD ports + adaptation layer + automatic
tests and validation
● Much better
● Gave us xorg-server 1.12 and contemporary
software

22. 22/28
A few words about Userland (3)
● Sadly, FreeBSD ports are beginning to lag
● Updating Cairo from 1.10 to 1.12 took years
● Still using xf86-video-intel 2.21.15
● Had to create a locally managed port of xf86-
video-intel 2.99.x
● Hope it won't become necessary for other parts

23. 23/28
Current state
● drm/i915 mostly in sync with Linux 3.8.13
– Not the GEM code
● drm/radeon mostly in sync with Linux 3.8
● drm/ttm in sync with Linux 3.9
● Generic drm code a mess
– A few parts up to Linux 3.8.13
– Others much much older (< Linux 2.6.26)

24. 24/28
Future directions
● Synchronize the drm code itself to Linux 3.8.13
– Required for key features like DRM Prime, DRM-
master, etc...
● Then start upgrading drm+drivers to more
recent versions
● Porting drm/nouveau also a good idea
– Should be easier now that ttm is working properly

25. 25/28
Future directions (2)
● Restore 80x25 VGA text mode after Xorg exit
● Currently black screen or frozen image
● Alternatively implement a graphical TTY layer
● Patches are floating around

26. 26/28
FreeBSD credits
● Konstantin Belousov
– Updated drm and drm/i915 to support gem+kms
– Ported most parts of drm/ttm to FreeBSD
● Alexander Kabaev
– Started to port the radeon driver
● Jean-Sébastien Pédron
– Finished the port of drm/radeon from Linux 3.8
– Critical fixes to drm/ttm

27. 27/28
DragonFly Credits
● François Tigeot: bulk of drm, drm/i915, drm/ttm
and drm/radeon porting
● Johannes Hofmann: made i915 work
● Matt Dillon: made i915 and ttm work reliably
– Added PAT support to the kernel
– fixed critical VM bugs
● Joris Giovanelli and Markus Pfeiffer: critical bug
investigations and fixes

28. 28/28
Questions ?