[yocto] [meta-raspberrypi] linux kernel rt

[Andreas Müller]

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:
>
>> On Thu, Dec 21, 2017 at 5:08 PM, Andrei Gherzan <andrei at gherzan.ro>
>> wrote:
>>
>>> Hi all,
>>>
>>> On Thu, Dec 14, 2017 at 12:09 PM, Andreas Müller <
>>> schnitzeltony at gmail.com> wrote:
>>>
>>>> On Thu, Dec 14, 2017 at 11:40 AM, Mirza Krak <mirza.krak at gmail.com>
>>>> wrote:
>>>>
>>>>> 2017-12-14 9:41 GMT+01:00 Andreas Müller <schnitzeltony at gmail.com>:
>>>>> > On Thu, Dec 14, 2017 at 2:58 AM, Sherif Omran <
>>>>> sherifomran2000 at gmail.com>
>>>>> > wrote:
>>>>> >>
>>>>> >> hey guys,
>>>>> >>
>>>>> >> any body tried the real time kernel? I get an error, it is snot in
>>>>> the
>>>>> >> compatibility list.
>>>>> >> can we skip it?
>>>>> >>
>>>>> >> thanks
>>>>> >>
>>>>> >> --
>>>>> >
>>>>> > Good news: I use RT kernel only together with VC4 graphics and have
>>>>> lots of
>>>>> > fun on PI2/3.
>>>>> > Bad news: As far as I know it is not in meta-raspberrypi but in my
>>>>> fork [1].
>>>>> > There were attempts to land the RT-patches in meta-raspberrypi but
>>>>> that was
>>>>> > denied for huge patch size :(
>>>>>
>>>>> If the patch size was the only problem one can pull it by doing the
>>>>> following in the recipe:
>>>>>
>>>>> SRC_URI += " \
>>>>>     https://cdn.kernel.org/pub/linux/kernel/projects/rt/4.9/patc
>>>>> h-4.9.65-rt56.patch.gz;name=rt-patch
>>>>> \
>>>>> "
>>>>>
>>>>> SRC_URI[rt-patch.md5sum] = "9caa7b541d8c84c2d5c5f58985982e95"
>>>>> SRC_URI[rt-patch.sha256sum] =
>>>>> "47dfb518c78d8cbaafd4ab9130eb26fe0170be9189b580ab26209ef679309539"
>>>>>
>>>>> Note that above sums are "random" and not the for the actually file
>>>>> but are there for reference.
>>>>>
>>>>> That way you do not need to keep a copy of it in meta-raspberrypi.
>>>>>
>>>>> --
>>>>>
>>>> Hi Mirza,
>>>>
>>>> Problem is that patches need alignments sometimes either caused by
>>>> Raspberry-Pi-specific adjustments or versions not matching exactly - RT
>>>> kernel patch updates are less frequent than kernel updates. Anyway: git is
>>>> very good at maintaining huge text content and this should not be a problem
>>>> these days. Another discussion about RT kernel was to have an extra kernel
>>>> for it and I never understood why. To me that seems nothing but an extra
>>>> maintenance burden.
>>>>
>>>> However - just wrote to Paul: I plan to be at FOSDEM and we can discuss
>>>> there how to get back to one layer only (not mine!) making everybody happy
>>>> :)
>>>>
>>>>
>>> I remember the discussion. Indeed that was the reason and the
>>> recommendation was to maintain a separate linux-raspberry fork where
>>> whoever has interest in this will maintain on top of linux-raspberrypi this
>>> patch. Obviously that didn't happen but I'd like to see it landing.
>>>
>>> Yes that was one of the suggestions which made me say 'Thanks - this is
>> just additional maintenance burden and will not work for long time - I do
>> my own'. FWIW: That suggestion came at a time when you (Andrei) seemed
>> overworked totally (just to mention - PLEASE don't take it as criticism - I
>> know what I am talking of when it comes to 'overworked').
>>
>
> You will be suprised but all of us are busy and this is a side project
> handled as good possible in our spare time. I do agree that there was a
> time where this project was a little demoted in priority. But even if that
> is the case, contributions are always welcomed - as you know.
>
>
>>
>> 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?

Some advertisement :) I would stand up to take care for RT and VC4 in the
future. This is what I need to build heavy heavy world builds with EGL/GLES
and able to mix/produce music..

Andreas
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.yoctoproject.org/pipermail/yocto/attachments/20171222/99620eca/attachment.html>