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Input-wacom backports

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Backporting commits into input-wacom

The "input-wacom" driver is a backported version of the upstream Wacom kernel drivers which allows users who are running older kernels to benefit from the latest updates. As patches are accepted upstream, it is necessary to ensure they are also added to input-wacom so the codebases stay in sync. This page outlines the steps so that the process can be followed without having to commit it to memory.

Prerequisites

Before beginning, you'll need to be sure your development machine has a copy of `git` installed and that you have clones of both the Linux kernel repository and our own input-wacom repository. Because development will not typically take place on Linus' upstream repository, additional "remotes" will need to be added that point to active development trees. The two remotes we deal most often with are Jiri's (HID subsystem) and Dmitry's (Input subsystem).

(kernel.git)~ git remote add jiri https://git.kernel.org/pub/scm/linux/kernel/git/jikos/hid.git
(kernel.git)~ git remote add dtor https://git.kernel.org/pub/scm/linux/kernel/git/dtor/input.git

In addition, to keep our Github mirror in sync with Sourceforge, it will need to be added as a "remote" of the input-wacom repository as well. Furthermore, if you would like the full benefit of our continuous integration tests, it is recommended to fork the Github repository and then sign up for a Travis-CI account. Once the fork has been made and the repository enabled in Travis-CI, you can add it as a remote as well:

(input-wacom.git)~ git remote add mirror https://github.com/linuxwacom/input-wacom.git
(input-wacom.git)~ git remote add fork https://github.com/${USERNAME}/input-wacom.git

The remainder of this document assumes that the remotes "jiri", "dtor", "mirror", and "fork" exist as described above. If you choose different names, please substitute them where necessary.

Importing Upstream Commits

Step 1: Navigate to your upstream kernel directory and fetch all upstream updates for the remotes. As git downloads the new commits, it will print out information about new branches and branches which have updates. New code which affects our driver could potentially be contained in any updated branch, but typically updates will only occur in Jiri's "wacom", "upstream", and "upstream-fixes" branches (as well as similar branches owned by Dmitry). Additionally, it is a good idea to periodically also check Linus' RC tags to ensure they don't contain any unexpected code.

In the sample below, we fetch updates for all upstream repositories by running `git remote update`. The output lists a number of branches of interest: "jiri/for-4.5/upstream", "jiri/for-4.5/upstream-fixes", "jiri/for-4.6/upstream", "jiri/for-4.6/upstream-fixes", and "jiri/for-4.6/wacom". Additionally, there are new RCs tagged by Linus that could also be investigated.

(kernel.git)~ git remote update
Fetching origin
remote: Counting objects: 319561, done.
remote: Compressing objects: 100% (76364/76364), done.
remote: Total 319561 (delta 251640), reused 296046 (delta 242417)
Receiving objects: 100% (319561/319561), 144.47 MiB | 2.51 MiB/s, done.
Resolving deltas: 100% (251640/251640), done.
From git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux
   b562e44..d3436a1  master     -> origin/master
 * [new tag]         v4.5       -> v4.5
 * [new tag]         v4.5-rc1   -> v4.5-rc1
 * [new tag]         v4.5-rc2   -> v4.5-rc2
 * [new tag]         v4.5-rc3   -> v4.5-rc3
 * [new tag]         v4.5-rc4   -> v4.5-rc4
 * [new tag]         v4.5-rc5   -> v4.5-rc5
 * [new tag]         v4.5-rc6   -> v4.5-rc6
 * [new tag]         v4.5-rc7   -> v4.5-rc7
 * [new tag]         v4.6-rc1   -> v4.6-rc1
 * [new tag]         v4.6-rc2   -> v4.6-rc2
Fetching jiri
remote: Counting objects: 149, done.
remote: Compressing objects: 100% (149/149), done.
remote: Total 149 (delta 98), reused 0 (delta 0)
Receiving objects: 100% (149/149), 147.53 KiB | 0 bytes/s, done.
Resolving deltas: 100% (98/98), done.
From git://git.kernel.org/pub/scm/linux/kernel/git/jikos/hid
 * [new branch]      for-4.5/upstream -> jiri/for-4.5/upstream
 * [new branch]      for-4.5/upstream-fixes -> jiri/for-4.5/upstream-fixes
 * [new branch]      for-4.6/cmedia -> jiri/for-4.6/cmedia
 * [new branch]      for-4.6/i2c-hid -> jiri/for-4.6/i2c-hid
 * [new branch]      for-4.6/logitech -> jiri/for-4.6/logitech
 * [new branch]      for-4.6/multitouch -> jiri/for-4.6/multitouch
 * [new branch]      for-4.6/penmount -> jiri/for-4.6/penmount
 * [new branch]      for-4.6/sony -> jiri/for-4.6/sony
 * [new branch]      for-4.6/thingm -> jiri/for-4.6/thingm
 * [new branch]      for-4.6/upstream -> jiri/for-4.6/upstream
 * [new branch]      for-4.6/upstream-fixes -> jiri/for-4.6/upstream-fixes
 * [new branch]      for-4.6/wacom -> jiri/for-4.6/wacom
   f212bd9..e1c9b9f  for-linus  -> jiri/for-linus
   369032a..ab99ccb  for-next   -> jiri/for-next
   851328f..d66435c  master     -> jiri/master

Step 2: For each branch or tag of interest from step 1, you will need to see if they contain any new commits that have not already been added to the input-wacom repository. The easiest way of doing this is to look at the last commit in each of input-wacom's upstream mirror branches. For example, we might find that the commit message of the last commit to our "jiri/for-4.5" branch contains the message "[jason.gerecke@wacom.com: Imported into input-wacom repository (0bbfe28)]". This indicates that the branch should contain all commits prior to 0bbfe28 and that anything newer may need to be added.

For each branch that may have new upstream commits (e.g., "jiri/for-4.5" and "jiri/for-4.6") take note of the commit ID mentioned in the last commit message.

Step 3: With the information gathered in step 2, we can have git export all commits newer than than that commit which affect our driver. To do this, we can run a command similar to the following example. The command should be run for each branch that may have new commits on it, replacing the commit SHA with the SHA from step 2 and the branch name with the branch of interest. The final path argument will depend on the remote -- for Jiri's branches you will want to use "drivers/hid/wacom*", while for Dmitry's use "drivers/input/touchscreen/wacom*".

(kernel.git)~ git format-patch 0bbfe28..jiri/for-4.5/upstream -- drivers/hid/wacom*
# No output.

If nothing is printed out, that means that none of the new upstream commits to "jiri/for-4.5/upstream" directly affect our driver. In such a case you can run the command again for the next branch of interest. If something is printed out, however, proceed to step 4 to integrate the patches into input-wacom.

(kernel.git)~ git format-patch 0bbfe28..jiri/for-4.5/upstream-fixes -- drivers/hid/wacom*
# No output.
(kernel.git)~ git format-patch f620516..jiri/for-4.6/wacom -- drivers/hid/wacom*
# No output.
(kernel.git)~ git format-patch f620516..jiri/for-4.6/upstream -- drivers/hid/wacom*
# No output.
(kernel.git)~ git format-patch f620516..jiri/for-4.6/upstream-fixes -- drivers/hid/wacom*
0001-HID-wacom-fix-Bamboo-ONE-oops.patch
0002-HID-wacom-Initialize-hid_data.inputmode-to-1.patch
0003-HID-wacom-Support-switching-from-vendor-defined-devi.patch

After checking several branches, each with no commits of interest, we see that 3 patches were generated for the "jiri/for-4.6/upstream-fixes" branch. We should now proceed to step 4 to integrate these patches into input-wacom.

Step 4: The patch files generated in step 3 will need to be slightly modified before importing them into the input-wacom repository. Firstly, we need to change the path to coincide with the path used by input-wacom:

(kernel.git)~ sed -i 's!drivers/hid/!3.17/!' *.patch

or

(kernel.git)~ sed -i 's!drivers/input/touchscreen!3.17!' *.patch

Secondly, we need to edit the files to add in the "Imported" message and a new "Signed-off-by" line to the end of the commit message. When writing the "Imported" message, the first 7 characters of the commit ID (listed in full on the first line of the patch file) should be used.

Step 5: At this point the files are ready and you can attempt to import them into the input-wacom repository:

(input-wacom.git)~ git am ${KERNELDIR}/*.patch

If a merge error occurs during the import process, git will suggest trying to apply the patch manually (e.g. with patch -p1 < .git/rebase-apply/patch). Go ahead and try this, and then resolve any patch errors by looking at the generated ".rej" files. Commit the fixed version, and then continue applying patches by running git am --continue.

Step 6: With all the patches successfully imported, it is now time to test them. Run `./configure && make` to verify everything compiles, `sudo modprobe -r wacom && sudo insmod 3.17/wacom.ko` to test things out. If any errors are encountered, you'll need to edit the buggy commit with the necessary changes.

Step 7: Once you've completed importing the patches from one upstream branch, you can remove the patch files from the kernel directory and return to step 3 with the next branch of interest. In this particular example, "jiri/for-4.6/upstream-fixes" was the last branch of interest so there was no need to return to step 3.

Step 8: Post your changes to the Linux Wacom developer list and push your changes with, for example:

~ git push fork dtor47:dtor/for-4.7
~ git push mirror dtor47:dtor/for-4.7
~ git push origin dtor47:dtor/for-4.7

Step 9: After all the upstream changes have been imported, the next step is to go see if any of them need to be backported to earlier kernel versions (e.g. 3.7, 2.6.38, etc.). Determining if a particular change needs to be backported will require an understanding of whether the change fixes a bug or adds a feature that is applicable to older kernel versions. Any backported changes should be added to the input-wacom "master" branch rather than one of the upstream mirror branches like "jiri/for-4.6".

Creating New input-wacom Branches

To accomplish the above you will need to create new branches when new branches are created at the (jiri, dtor, etc) kernel remotes. To do this, merge master on to the current (soon to be old) import branch (eg jiri/for-4.5). Then create a new import branch from the current (now 'old') import branch. Then push those branches up to origin.

$ git merge master
$ git branch j46
$ git push origin j45:jiri/for-4.5
$ git push origin j46:jiri/for-4.6

Also merge the 'old' current branch (eg j45) into master.

$ git checkout master $ git merge j45

Backporting Patches to Earlier Kernels

Backporting requires an understanding of the history of the driver, so it is not as step-by-step as the importing to 3.17 done above.

As of May 2016, 3.17 is the newest kernel driver in input-wacom. There are 4 older kernel drivers to backport patches to. These older kernel drivers are are 3.7, 2.6.38. 2.6.36, and 2.6.30. 3.7 and 2.6.38 are closer to the 3.17 driver while 2.6.36 and 2.6.30 have been diverged from.

Whereas imports to the newest driver (3.17) are done on the (jiri/dtor)/for-x.x branches, backports to the older kernels are done on master. To begin, find all of the existing patches on the jiri/dtor branches (see above) which have not been merged into master. Our job will be to determine how, and if, to 'backport' (or replicate these changes) for the older kernels.

The following types of changes will be encountered: new features, new devices, bug fixes, upstream code refactoring, and upstream code cleanup. In general, we only backport new features, new devices and bug fixes which are relevant to the older kernels. Upstream code refactoring and cleanup are considered on a case-by-case basis.

Some bits of knowledge about backporting

Kernel 2.6.36 has a transitional touch system. Patches for new devices which have touch are mostly not backported to this branch.

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