Re: [Ksummit-discuss] [Stable kernel] feature backporting collaboration

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Ted,

On Monday 05 Sep 2016 10:03:27 Theodore Ts'o wrote:
> On Mon, Sep 05, 2016 at 12:11:05PM +0100, Mark Brown wrote:
> > On Mon, Sep 05, 2016 at 04:28:44AM +0530, Amit Kucheria wrote:
> >> The vendors depend on Google providing an Android common tree[1] to
> >> build their BSP on top of. Currently, there isn't anything newer than
> >> a 4.4-based common tree from Google. It'll be early 2017 by the time
> >> 4.9 LTS is released and the Android common tree is available on it
> > 
> > It's not just having an Android tree either, it's having an Android tree
> > that they're confident is actively used and tested by Google.  Simply
> > making a tree available wouldn't be enough, that was tried in the past.
> 
> One of the problems is I can't test the Android common tree, because I
> don't have access to hardware that I can boot on that tree.  (To be
> honest, I'm not even sure what hardware would boot on it.)  And thanks
> to the tender loving care the SOC vendors have lavished on on their
> BSP kernels, if there has been BSP "value added patches" from ARM SOC
> vendors applied to a kernel tree, chances are extremely high that you
> can no longer do testing using kvm-xfstests.  (In some cases I was
> able to bash the tree enough that it would boot under kvm/x86, but in
> many cases, the ARM SOC changes were so horrible that it was
> hopeless.)
> 
> This is why upstream-first is so darned important.  And why sloppy
> patches that break other architectures are a really bad idea, even if
> they are for a vendor-only BSP kernel....
> 
> Maybe there will be some hope if some of the features from ARM64
> server can infect the SOC community --- Jon Masters really had the
> right idea when he insisted on one kernel to boot all ARM64 kernels,
> with all changes pushed upstream, and not hacky, out-of-tree patches
> which only work for one SOC vendor.

I don't think that's a fair comparison. For server platforms end-users of the 
hardware will pick a distribution and roll it out on the machines, so hardware 
vendors have a strong incentive to play by our rules. Phones are completely 
different in that the device vendor doesn't care about end-users being able to 
pick what software in general and kernel in particular they want to install on 
the device. Worse than that, many vendors go through hoops and loops to make 
that impossible. Unless customers start boycotting devices that are not 
upstream-friendly - and I don't think anyone expects this to happen - we'll 
need to give SoC vendors a different incentive.

-- 
Regards,

Laurent Pinchart