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[Clinton <cssprain@xxxxxxxxx>]

** Tags added: kernel-bug-exists-upstream

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https://bugs.launchpad.net/bugs/1264426

Title:
  Appletouch driver moves cursor in steps

Status in “linux” package in Ubuntu:
  Confirmed

Bug description:
  When using the appletouch driver on a Macbook 3,1, the cursor moves in
  noticeable horizontal or vertical 'steps'. This is particularly
  noticeable when dragging a diagonal line. This can make the trackpad
  very difficult to use, as it becomes hard to hone in on small objects,
  particularly if the user has opted for a faster cursor. This issue is
  also described in a forum thread:
  http://ubuntuforums.org/showthread.php?t=813884&page=6

  There is a workaround that involves modifying and recompiling
  appletouch.c with a couple of changes. This is also detailed in bug
  #1034132.

  Original:
  #define ATP_FUZZ 16
  #define ATP_THRESHOLD 5

  New:
  #define ATP_FUZZ 0
  #define ATP_THRESHOLD 2

  This makes the trackpad much more usable, though slight stepping is
  still noticeable. I've found the modification below seems to provide a
  small amount of additional smoothness:

  Original:
  pcum += (xy_sensors[i] - threshold) * i;
  psum += (xy_sensors[i] - threshold);

  New:
  pcum += (xy_sensors[i]) * i;
  psum += (xy_sensors[i]);

  Another change that seems to help is using more than one previous
  cursor sample when averaging out the movement towards the desired new
  cursor position:

  Original:
  x = (dev->x_old * 3 + x) >> 2;
  y = (dev->y_old * 3 + y) >> 2;

  New:
  x = (dev->x_older + dev->x_old * 2 + x) >> 2;
  y = (dev->y_older + dev->y_old * 2 + y) >> 2;

  Put together, these changes make the stepping as close to
  imperceptible as can be reasonably expected given the hardware.

  Regression testing will be necessary on the earlier (pre-geyser 4)
  models to rule out the possibility that these changes would just be
  trading better behavior for some models at the expense of others; if
  that were the case, some conditional logic would be in order.

  I expect this bug to hit a larger audience as owners of Macbooks too
  old for OS X Mavericks begin to migrate to Linux.

  ProblemType: Bug
  DistroRelease: Ubuntu 14.04
  Package: linux-image-3.12.0-7-generic 3.12.0-7.15
  ProcVersionSignature: Ubuntu 3.12.0-7.15-generic 3.12.4
  Uname: Linux 3.12.0-7-generic x86_64
  ApportVersion: 2.12.7-0ubuntu3
  Architecture: amd64
  AudioDevicesInUse:
   USER        PID ACCESS COMMAND
   /dev/snd/controlC0:  ubuntu     2706 F.... pulseaudio
  CasperVersion: 1.336ubuntu1
  CurrentDesktop: Unity
  CurrentDmesg:
   [   31.859199] sky2 0000:03:00.0 eth0: Link is up at 1000 Mbps, full duplex, flow control both
   [   31.859229] IPv6: ADDRCONF(NETDEV_CHANGE): eth0: link becomes ready
   [  299.816181] mce: [Hardware Error]: Machine check events logged
  Date: Fri Dec 27 03:05:13 2013
  IwConfig:
   eth0      no wireless extensions.

   lo        no wireless extensions.
  LiveMediaBuild: Ubuntu 14.04 LTS "Trusty Tahr" - Alpha amd64 (20131226)
  MachineType: Apple Inc. MacBook3,1
  ProcFB: 0 inteldrmfb
  ProcKernelCmdLine: BOOT_IMAGE=/casper/vmlinuz.efi file=/cdrom/preseed/username.seed boot=casper quiet splash --
  RelatedPackageVersions:
   linux-restricted-modules-3.12.0-7-generic N/A
   linux-backports-modules-3.12.0-7-generic  N/A
   linux-firmware                            1.117
  RfKill:
   0: hci0: Bluetooth
    Soft blocked: no
    Hard blocked: no
  SourcePackage: linux
  UpgradeStatus: No upgrade log present (probably fresh install)
  dmi.bios.date: 03/05/08
  dmi.bios.vendor: Apple Inc.
  dmi.bios.version: MB31.88Z.008E.B02.0803051832
  dmi.board.asset.tag: Base Board Asset Tag
  dmi.board.name: Mac-F22788C8
  dmi.board.vendor: Apple Inc.
  dmi.board.version: PVT
  dmi.chassis.asset.tag: Asset Tag#
  dmi.chassis.type: 2
  dmi.chassis.vendor: Apple Inc.
  dmi.chassis.version: Mac-F22788C8
  dmi.modalias: dmi:bvnAppleInc.:bvrMB31.88Z.008E.B02.0803051832:bd03/05/08:svnAppleInc.:pnMacBook3,1:pvr1.0:rvnAppleInc.:rnMac-F22788C8:rvrPVT:cvnAppleInc.:ct2:cvrMac-F22788C8:
  dmi.product.name: MacBook3,1
  dmi.product.version: 1.0
  dmi.sys.vendor: Apple Inc.

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