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Kernel development cycle

Hi, please help me understand some general practices involved in kernel development. Specifically, I'm interested in how patches are included or reverted in different kernel versions.


Let's consider a practical example, the history of patch "drm/i915/execlists: Reset RING registers upon resume" [1]. This patch was committed 641 commits after version 4.8-rc2:


$ git describe bafb2f7d4755bf1571bd5e9a03b97f3fc4fe69ae



So I would expect to find it in version 4.8, which is the stable, final release of v4.8, following all the release canditates.


However, if I search for the tag that follows (and hence contains) that commit, I do not find version 4.8, nor version 4.9, but 4.10:


$ git describe --contains bafb2f7d4755bf1571bd5e9a03b97f3fc4fe69ae



Why? Why not v4.8-rc3? This means that the patch has been included neither in v4.8 nor in v4.9, but only in version 4.10-rc1, right? Why so much time was needed, considering it was the 621st commit on top ov v4.8-rc2?


Another thing that confuses me is the following. In fact that patch ended up in v4.9.9 [2]. If my reasoning above is correct, it was backported from v4.10, right?


Then some problems were reported, and it was reverted in v4.9.23 with commit 0ee72d8f9b8e17b8e4ccfebc7a25cbc2d395cd6a [3]. (What led to the decision of reverting it is explained in [4] and [5]).


So my question now is--what version contains this patch? Is it true that I find it in v4.10?


Stretch currently provides kernel version 4.9.30:


$ uname -v

#1 SMP Debian 4.9.30-2+deb9u2 (2017-06-26)


Since v4.9.30 follows v4.9.23, the patch is not be included in Stretch's kernel, so this explains why I'm experiencing the bug addressed by this patch.


Thanks for your help.


[1] https://patchwork.freedesktop.org/patch/111587/

[2] https://www.kernel.org/pub/linux/kernel/v4.x/ChangeLog-4.9.9

[3] https://www.kernel.org/pub/linux/kernel/v4.x/ChangeLog-4.9.23

[4] https://bugs.freedesktop.org/show_bug.cgi?id=100221#c10

[5] http://mid.mail-archive.com/1489443835.5568.7.camel@xxxxxxxxxxx



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