On 12/20/2017 10:43 AM, Daniel Vetter wrote:

On Tue, Dec 19, 2017 at 07:40:12PM +0100, Max Staudt wrote:

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On 12/19/2017 06:26 PM, Daniel Vetter wrote:

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So essentially you're telling me that on a current general purpose
distro the gfx driver loading is a dumpster fire, and we're fixing
this by ignoring it an adding a hole new layer on top. That doesn't
sound like any kind of good idea to me.

Yes. It is a vast improvement over the status quo, and people are asking
for it. And the bootsplash layer can be moved elsewhere, just change the
hooks and keep the loading/rendering.

Also, gfx driver loading isn't a dumpster fire, it mostly just works. It
just mustn't be done 100% carelessly.

You've talked about using sleep and stuff to paper over races. That
doesn't sound good at all.

Sorry, I was unclear.

It's Plymouth's ShowDelay that, unintentionally, papers over this bug.

The driver loading bug will happen with any user based splash - it's not limited to Plymouth.

On the other hand, if you don't start a graphical application before having loaded the final graphics driver, everything is good and there is no race.

So, module loading works as intended ;)

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So if just using drm for everything isn't possible (since drm drivers
can at least in theory be hotunplugged), can we at least fix the
existing fbdev kernel bugs? Not being able to unplug a drm driver when
it's still open sounds like a rather serious issues that probably
should be fixed anyway ... so we're better able to hotunplug an fbdev
driver when it's in use.

I don't see it as a bug. The fbdev driver gets unloaded as much as
possible, but as long as a userspace application keeps the address_space
mmap()ed, there's nothing we can do, short of forcibly removing it and
segfaulting the process the next time it tries to render something. Am I
missing something?

I guess you could remap that too ... But yeah SIGBUS ftw. Wrap rendering
in a sighandler and abort if you hit that. In drm we try to be a bit
better and keep things around until userspace has gone.

Hmm. Are you sure it's okay to SIG these processes just because someone else has decided to unload a driver? That is counter to everything else that I've seen so far.

Also, is it even feasible, implementation wise?

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Or we get simpledrm merged (for efifb and vesafb support) and someone
types the xendrm driver (there is floating around, it's just old) and
we could forget about any real fbdev drivers except the drm based
ones.

And drmcon, unless we come up with a better idea than hooking into the *con driver.

If we have everything as drm drivers, you can just use plymouth (with no
fbdev backend ofc) and everyone is happy. Including the efifb folks (it's
simply going to be called efidrmfb or something like that). So no idea why
you need a *con.

Hmm, that still makes us wait until userspace has appeared...

And the reason I built it into *con is because the logic for appearing/disappearing is basically the same, and in this chain it makes sense for the bootsplash show/hide logic to be chained behind *con.

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Sure, that'd help a lot. But what do we do until then?

Make it happen? Twiddling thumbs is an option too ofc, but it tends to not
result in results :-)

I'm afraid I don't have the time to write an in-kernel terminal emulator, thus the wish to build upon the existing one...