[Raspbian-devel] Neon enablement in qt for raspbian.

[Peter Green]

Back when Mike and I founded raspbian, there was only the pi1. Packages 
that used neon often set off our armv7 contamination checker and at the 
time we saw neon support in raspbian as at best a pointless waste of 
space and at worst a problem, so we simply disabled it wherever we ran 
into it.

However times have changed. The raspberry pi 2 and 3 have been released 
and Raspberry Pi want to continue shipping a single image for all their 
products for the forseable future.

As a result I am currently working on re-enabling neon in raspbian where 
appropriate. I have been doing the work in raspbian jessie and intend to 
forward port it to raspbian stretch later. Clearly since we still 
support the original raspberry pi and the new pi0 only packages with 
correctly functioning neon runtime detection are candidates for neon 
enablement.

There are two qt source packages in raspbian jessie where we currently 
have neon disabled. qt4-x11 and qtbase-opensource-src . I have a couple 
of questions.

1: are these packages supposed to have runtime neon detection (either in 
the packages own code or through ld.so hwcaps).
2: For each of the packages can anyone suggest a simple benchmark/test 
that will hit the neon codepaths which I can use to check that neon 
detection is doing it's job (i.e. that the package still works on the 
pi1 and there is a performance improvement over the package without neon 
on the pi2)