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Date:   Mon, 11 Feb 2019 20:55:09 +0800
From:   Tom Li <tomli@tomli.me>
To:     Alexandre Oliva <lxoliva@fsfla.org>
Cc:     James Hogan <jhogan@kernel.org>,
        Jiaxun Yang <jiaxun.yang@flygoat.com>,
        Huacai Chen <chenhc@lemote.com>,
        Ralf Baechle <ralf@linux-mips.org>, linux-mips@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [RFC] On the Current Troubles of Mainlining Loongson Platform
 Drivers
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On Mon, Feb 11, 2019 at 10:13:00AM -0200, Alexandre Oliva wrote:
> On Feb  8, 2019, Tom Li <tomli@tomli.me> wrote:
>=20
> > found Alexandre Oliva has stopped maintaining his tree
>=20
> ?!?
>=20
> I still merge and tag every one of Torvalds' and Greg KH's releases into
> the loongson-community tree, resolving trivial conflicts and trying to
> verify that it at least builds and passes a smoke test on actual
> hardware (after Linux-libre deblobbing, but still).

What is the current link to your repository? The original one from Lemote
is now a 404, and the GitHub one has been "archived".

> Two issues that bother me a bit are frequent failure to reboot/poweroff,
> that's been around since around 4.10, and, more recently, a very slow
> system overall, that's been present since 4.20.  I haven't checked
> whether they're caused by changes in the loongson-community tree that I
> still carry, or if they're already present in upstream releases.
>=20
> I've already tried to bisect the former, but since the issue is
> intermittent, that proved to be too tricky and time-consuming for me.
>=20
> I haven't tried to bisect the latter yet.

You cannot bisect it. Because I've tried it for 24 hours without sleep, but
failed. ;-)

We've just identified and confirmed the source of the shutdown problem a
few days ago on this mailing list. It's related to a PREEMPT race condition
in the cpufreq framework that triggers a timing-dependent, probabilistic
lockup in the i8259 PIC driver. And it was first noticed by Ville Syrj=E4l=
=E4
on a x86 system, my debugging rediscovered his findings.

You can read the full investigation at here:
https://lkml.org/lkml/2018/11/13/857

You can pick up the patch from:
https://lore.kernel.org/lkml/20190207205812.GA11315@darkstar.musicnaut.iki.=
fi/

A patch has been authored and submitted by Aaro Koskinen, but currently it
seems stuck in the mailing list because the maintainer worries about regres=
sion
and asks for testing on more MIPS systems, although we believe it's a trivi=
al
patch.

In addition, I've discovered and fixed another bug preventing the machine f=
rom
shutting down, this patch has already merged into the Linus tree.

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?=
id=3D8a96669d77897ff3613157bf43f875739205d66d

> and, more recently, a very slow system overall, that's been present since
> 4.20.

The mainline framebuffer driver doesn't have any hardware drawing, printing
even a single line on the console is required a full screen redraw via memo=
ry-
mapped I/O over the slow PCI interface. I have rebased the 2D acceleration
code against the latest upstream driver and sent the patch to the fbdev mai=
ling
list on February 2nd.=20

But the maintainers seem to be working on other tasks and the patches (incl=
uding
mine and others') on the list didn't receive any response.

It's avaliable from

https://patchwork.kernel.org/project/linux-fbdev/list/?series=3D75029

> I've considered leaving the loongson-community tree behind and using
> upstream releases, but every time I was about to do that, something else
> came up that led me to keep at it.  I think the last such occurrence was
> the removal of the video driver (later reintroduced as a new driver).
> So I've kept at it ;-)

I'll continue working on upstreaming these out-of-tree drivers as my person=
al
project. I hope you'll be able to use a fully-functional machine with the m=
ainline
kernel soon, my current target is Linux 5.3.

Cheers,
Tom Li

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