[yocto] [meta-raspberrypi] linux kernel rt

[Andreas Müller]

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').

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.

Cheers,

Andreas
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