[yocto] [meta-raspberrypi][PATCH v2] linux-raspberrypi-rt: add

[Trevor Woerner]

On Thu, Jan 5, 2017 at 4:59 PM, Paul Barker <paul at paulbarker.me.uk> wrote:
> On Thu, 5 Jan 2017 15:16:19 -0500
> Trevor Woerner <twoerner at gmail.com> wrote:
>
>> On Thu 2017-01-05 @ 07:33:38 PM, Paul Barker wrote:
>> > On Thu,  5 Jan 2017 12:42:29 -0500
>> > Trevor Woerner <twoerner at gmail.com> wrote:
>> >
>> > > Add an -rt kernel recipe for Raspberry Pi that includes the FIQ patch which
>> > > adds stability to the -rt kernel (with full preemption enabled) and is an
>> > > improvement to simply disabling FIQ on the kernel cmdline.
>> > >
>> > > Signed-off-by: Trevor Woerner <twoerner at gmail.com>
>> > > ---
>> > >
>> > > changes since v1:
>> > >   - use "make savedefconfig" to generate the defconfig instead of just
>> > >     using the full .config
>> > >
>> > >  .../0001-fix-dtbo-rules.patch                      |    44 +
>> > >  .../FIQ_PREEMPT_RT_on_raspi.patch                  |   310 +
>> > >  .../linux/linux-raspberrypi-rt-4.4/defconfig       |  1249 +
>> > >  .../patch-4.4.32-rt43.patch                        | 31403 +++++++++++++++++++
>> > >  recipes-kernel/linux/linux-raspberrypi-rt_4.4.bb   |    55 +
>> > >  5 files changed, 33061 insertions(+)
>> > >  create mode 100644 recipes-kernel/linux/linux-raspberrypi-rt-4.4/0001-fix-dtbo-rules.patch
>> > >  create mode 100644 recipes-kernel/linux/linux-raspberrypi-rt-4.4/FIQ_PREEMPT_RT_on_raspi.patch
>> > >  create mode 100644 recipes-kernel/linux/linux-raspberrypi-rt-4.4/defconfig
>> > >  create mode 100644 recipes-kernel/linux/linux-raspberrypi-rt-4.4/patch-4.4.32-rt43.patch
>> > >  create mode 100644 recipes-kernel/linux/linux-raspberrypi-rt_4.4.bb
>> > >
>> >
>> > Would it be possible to point SRC_URI at kernel.org [1] instead of
>> > including the whole patch in meta-raspberrypi? It feels a bit much to
>> > me to include a >1MB patch file.
>> >
>> > [1]: https://www.kernel.org/pub/linux/kernel/projects/rt/4.4/older/patch-4.4.32-rt43.patch.gz
>>
>> The "virgin" -rt patch from kernel.org doesn't apply cleanly. First off there
>> is a slight version mismatch and secondly this is the raspberrypi kernel, not
>> a pure upstream kernel.
>>
>> Is there a way to patch a patch before it gets applied? If it could be
>> fetched from kernel.org then patched before applying that would be ideal!
>> The diff isn't that big; it's sad to have to provide a >1MB patch for such
>> a small tweak. I guess that's why the yocto kernels/patches have their own
>> repositories on yoctoproject.org?
>
> I think it depends how you want to maintain it going forward. With
> frequent upgrades to linux-raspberrypi I can see that >1MB patch being
> modified very often and I'm not sure how good it will be for the git
> repository size and efficiency.

Okay, agreed.

> A linux-raspberrypi-rt repository on GitLab[1] or some other git hosting
> service may be a good idea. I can see this having value outside the
> OpenEmbedded/Yocto Project world, especially if the vanilla -rt patches
> don't directly apply to linux-raspberrypi. If you decide to go this
> route and need any support to make it happen, let me know and I'll see
> what I can do.

Sounds good... and Wow! GitLab looks awesome! I guess I'll look at how
the yocto kernels are managed and see if it applies.

> Also, are you thinking of moving the -rt recipe to the 4.9 series when
> upstream linux-raspberrypi declares that stable?

Yes.

> When they declared 4.4
> stable they stopped updating the 4.1 series pretty much immediately. I'm
> currently investigating whether there is any value in maintaining the
> 4.4 series ourselves after upstream moves on.

I want to see how managing one goes.