Re: i915 4.5 bugfix backport and release management issue?

[Daniel Vetter]

On Tue, Mar 29, 2016 at 6:16 PM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:
> On Tue, Mar 29, 2016 at 12:49 AM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:
>> On Tue, Mar 29, 2016 at 12:43 AM, Daniel Vetter <daniel.vetter@xxxxxxxx> wrote:
>>> On Tue, Mar 29, 2016 at 4:39 AM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:
>>>> AFAICT something got rather screwed up in i915 land for 4.5.
>>>>
>>>> $ git log --oneline --grep='Pretend cursor is always on' v4.5
>>>> drivers/gpu/drm/i915/
>>>> e2e407dc093f drm/i915: Pretend cursor is always on for ILK-style WM
>>>> calculations (v2)
>>>>
>>>> $ git log --oneline --grep='Pretend cursor is always on' v4.6-rc1
>>>> drivers/gpu/drm/i915/
>>>> e2e407dc093f drm/i915: Pretend cursor is always on for ILK-style WM
>>>> calculations (v2)
>>>> b2435692dbb7 drm/i915: Pretend cursor is always on for ILK-style WM
>>>> calculations (v2)
>>>>
>>>> The two patches there are almost, but not quite, the same thing, which
>>>> makes me wonder how they both ended up in Linus' tree without an
>>>> obvious merge conflict.
>>>>
>>>> I have no idea what caused this.  However, I think (on very little
>>>> inspection, but it's consistent with problems I have with 4.5 on my
>>>> laptop) that the first one is an *incorrect* fix for a regression in
>>>> 4.5 and the second is a correct fix for the same regression.  4.6-rc1
>>>> seems okay.
>>>>
>>>> I reported the regression and everyone involved has known about it for
>>>> weeks.  Nonetheless, 4.5 final is busted.
>>>
>>> Quoting from e2e407dc093f
>>>
>>> "(cherry picked from commit b2435692dbb709d4c8ff3b2f2815c9b8423b72bb)"
>>>
>>> i.e. this is intentionally twice in the history. We started to soak
>>> bugfixes in -next and then cherry pick them because we had too much
>>> fun with things blowing up, and also too much fun with really messy
>>> conflicts. It's not a botched patch in 4.5 or anything else nefarious
>>> at all.
>>
>> Bah, sorry, I read it wrong.  They have the same final state but they
>> were on different bases.  I somehow reversed this in my head and
>> thought they had the same initial state and different final states.
>>
>
> Also, sorry for the excessive diatribe.  I plead sleepiness and
> mis-reading of code.

Thanks. We really appreciate friendly discussions here on intel-gfx,
the technical challenges are hard enough as is.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch