Re: [PATCH 3/3] drm/vkms: fbdev emulation support

From: Pekka Paalanen <ppaalanen@gmail.com>
To: Daniel Vetter <daniel@ffwll.ch>
Cc: Haneen Mohammed <hamohammed.sa@gmail.com>,
	Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>,
	Neil Armstrong <narmstrong@baylibre.com>,
	DRI Development <dri-devel@lists.freedesktop.org>,
	Melissa Wen <melissa.srw@gmail.com>,
	Thomas Zimmermann <tzimmermann@suse.de>,
	Daniel Vetter <daniel.vetter@intel.com>
Subject: Re: [PATCH 3/3] drm/vkms: fbdev emulation support
Date: Tue, 13 Oct 2020 13:19:38 +0300	[thread overview]
Message-ID: <20201013131938.73a5d1c6@eldfell> (raw)
In-Reply-To: <CAKMK7uHY_nrB=0-xkWi+FXFosCY1XPVXLJb+mGqDR+GpRZ6C6Q@mail.gmail.com>

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On Tue, 13 Oct 2020 09:53:44 +0200
Daniel Vetter <daniel@ffwll.ch> wrote:

> On Tue, Oct 13, 2020 at 8:14 AM Pekka Paalanen <ppaalanen@gmail.com> wrote:
> >
> > On Mon, 12 Oct 2020 16:23:35 +0200
> > Daniel Vetter <daniel@ffwll.ch> wrote:
> >  
> > > On Mon, Oct 12, 2020 at 02:40:58PM +0200, Neil Armstrong wrote:  
> > > > Hi,
> > > >  
> >
> > ...
> >  
> > > > It's weird because it the kernel is misconfigured and no console is specified on the cmdline
> > > > this console could become the main console...
> > > >
> > > > It's a great feature, but couldn't this be a module parameter ?  
> > >
> > > If you have vkms enabled in a distro, you're doing it wrong.  
> >
> > That's really not a great position to take. I would prefer that
> > if a random contributor writes a Weston patch and runs 'meson test', it
> > will use VKMS to run Weston's DRM-backend tests on his machine
> > automatically, maybe save for some seat and device node access
> > permissions bits which distributions could be delivering as well.
> >
> > Just put the VKMS device node into a non-default seat, and Xorg etc.
> > will happily ignore it.
> >
> > For the fbdev device node, I don't know. Maybe a module parameter
> > really is a good choice there, defaulting to off. I have no interest in
> > testing anything against fbdev, but other people might disagree of
> > course.
> >
> > Why? Gitlab CI is still not running tests for every commit, just per
> > MR, and it might even be infeasible too.
> >
> > I am also hoping for a future where I don't have to build my own kernel
> > just to be able to run Weston DRM tests with VKMS. That means I want to
> > be able to run my machine with VKMS loaded and active at all times,
> > without affecting the normal desktop. I already have such a setup with
> > an extra AMD card, but you can't run most KMS tests against real
> > hardware drivers.  
> 
> I just realized that building vkms is no problem, since it doesn't
> auto-load. And if our Grand Plans with configurability come true, then
> your test-harness will want to do that loading and setup itself
> anyway. With that there also shouldn't be any problems with fbcon,
> since presumably you already have that bound to the real gpu.
> 
> So I think we're all fine here, for everyone.
> 
> Now if you built-in vkms, that's a different thing. And for that I
> really think a "don't do that" is the right choice.

Very good.

My remaining wish is that VKMS would be fully configurable and usable
by an ordinary user, but I suppose that should be solved with a
privileged userspace daemon somewhat similar to logind that hands out
VKMS "sessions" somehow.

Not sure configfs is the best choice for VKMS configuration, unless
maybe unprivileged userspace could ask for a VKMS instance with its own
configfs tree it can access without CAP_ADMIN...

Thanks,
pq

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