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Date:      Thu, 7 Nov 2019 16:00:50 -0600
From:      "Matthew D. Fuller" <fullermd@over-yonder.net>
To:        Niclas Zeising <zeising@freebsd.org>
Cc:        freebsd-x11@freebsd.org
Subject:   Re: drm-fbsd11.2-kmod on 12
Message-ID:  <20191107220050.GA3169@over-yonder.net>
In-Reply-To: <77bac16b-0438-b7ed-0c44-fadc230e55f8@freebsd.org>
References:  <20191103231435.GH86455@over-yonder.net> <3231b40d-1041-10d2-f062-eda237e07a02@freebsd.org> <20191106230916.GI86455@over-yonder.net> <77bac16b-0438-b7ed-0c44-fadc230e55f8@freebsd.org>

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On Thu, Nov 07, 2019 at 09:41:20AM +0100 I heard the voice of
Niclas Zeising, and lo! it spake thus:
> 
> What issues are you seeing with the 4.16 branch?  Have you reported
> this?

On one machine with radeonkms and a Radeon 6450, it will eventually
crash when using vdpau output for videos (I believe even with formats
that don't get hardware accelerated).  It doesn't happen
deterministically, but on a frequency of maybe a few percent of the
time.  4.11 is perfectly fine with it, and 4.16 hasn't shown any
surprises without vdpau, so that's reasonably easily workaroundable in
practice.

On my main workstation, with amdgpu and a Radeon wx2100 (roughly
550-something-ish), it will crash out without obvious trigger, on the
order of maybe twice a week.  Playing video, not playing video,
scrolling in a browser, not scrolling in a browser, xlock'd and DPMS'd
off, everything on, etc.  As I recall, backtraces wound up pointing at
not much after ioctl handlers, bearing some resemblance to the stuff
in GH issue #149 (though I'm on the different driver), and I believe
once that looked more like #130 with the ttm funcs (with similar to
both showing up in the BZ bug linked from there).  I don't have any of
the cores still around though; I switched back to 4.11 last year, and
it's been solid since.


Part of the difficulty with this being so much upstream-y code that
we're a ways behind on, is that I know it can be really hard to
separate "we cause this problem by a mistake in porting" vs "this is a
bug in the pure code" (especially of the "... and is fixed in later
upstream versions already" variant).  So I figure the best way to get
it fixed is to desperately strive to not distract the people trying to
catch up to upstream, and more up-to-date-ish upstream code will
either have fixed their bug, or make it more certain that it's
something on our side causing it.  Either way, there's more to work
with than "it crashes every couple days"...


> Getting 4.11 running on FreeBSD 12.1 would require some effort, and
> I believe that effort is much better spent elsewhere.

I figured it would actually be relatively simple; it works fine with a
mid-July stable/12, and there's only a half dozen or so commits on the
drm-v4.16-fbsd12.0 branch since then, so I expect I can probably get
it working just by backporting a couple of them.  (I _was_ asking "has
anybody who knows this code already done this work?", more than "hey,
can you guys do this for me?")


-- 
Matthew Fuller     (MF4839)   |  fullermd@over-yonder.net
Systems/Network Administrator |  http://www.over-yonder.net/~fullermd/
           On the Internet, nobody can hear you scream.



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