[yocto] [meta-raspberrypi] linux kernel rt

[Paul Barker]

On Fri, Dec 22, 2017 at 2:17 PM, Andreas Müller <schnitzeltony at gmail.com> wrote:
> On Fri, Dec 22, 2017 at 2:25 PM, Andrei Gherzan <andrei at gherzan.ro> wrote:
>>
>> Hi Andreas,
>>
>> On Thu, Dec 21, 2017 at 8:59 PM, Andreas Müller <schnitzeltony at gmail.com>
>> wrote:
>>>
>>>
>>> Why not simply one stable kernel with RT-patches applied if user decides
>>> by an option? That is what I am doing for >1 year now and meta-raspi-light
>>> is the one which caused me least efforts/headaches of all. And yes I know I
>>> made life easy here by removing userland completely and taking care for
>>> RPi2/3 only.
>>>
>>
>> I will always advocate against forks but definitely that is an option too.
>> What I want to understand is why maintaining it in meta-raspberrypi was
>> painful. Basically, the question is how do you currently maintain, rebase
>> etc the rt patch? I would expect it to happen in a git tree as well. Isn't
>> that the case?
>>
> I maintained it this way:
>
> * Set new kernel version
> * Check if there is an update at RT-Kernel. If so update the patch.
> * Rebuild the kernel. In case a patch does not apply cleanly, I use git
> inside of oe work-shared folder, check/align for hunks failing and insert
> them manually into original patch. From my experience there are usually very
> few hunks to touch so this is no rocket science.
>
> What do you think?
>

So, my thinking was that if you're going through the effort of getting
the -rt patches to apply to the rpi kernel, I'd like to see that
available to non-OpenEmbedded users. I think a linux-raspberrypi-rt
kernel tree would be a useful think to make available as a standalone
project, which we can then pull into meta-raspberrypi as a simple
recipe.

My complaint with having the entire -rt patch in the meta-raspberrypi
repo was that it's a huge, un-reviewable blob. Multi-thousand line
patches are now less painful with review happening on GitHub now
though - they at least don't upset my email workflow anymore :)

Could you try handling this in git by merging the -rt kernel branch
(https://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-stable-rt.git/log/?h=v4.9-rt)
into the linux-raspberrypi branch regularly instead of by applying the
-rt patch manually? Any merge conflicts could be handled cleanly that
way and it would give us something we could bisect properly in case of
any bugs. The resulting git repository could be published online as
something like 'linux-raspberrypi-rt' if this works.

This is basically my opinion though, there is no one true Right Way
(TM) to do this. If you decide it's still easier for you to handle
this as a patch in the meta-raspberrypi layer then I'm happy to
support that.

-- 
Paul Barker
Togán Labs Ltd