Re: Switching fb backend back to default

On Sun, Mar 17, 2019 at 21:35 Emmanuel Vadot <manu_at_bidouilliste.com> wrote:

> On Sun, 17 Mar 2019 16:32:43 +0000
> Johannes Lundberg <johalun0_at_gmail.com> wrote:
>
> >
> > On 3/17/19 3:34 PM, Greg V wrote:
> > >
> > >
> > > On Sun, Mar 17, 2019 at 3:07 PM, Johannes Lundberg
> > > <johalun0_at_gmail.com> wrote:
> > >> Hi
> > >>
> > >> I'm working on making i915kms unload properly. I've come to what I
> think
> > >> is the last issue. The drm driver unloads ok, the "efifb" backend is
> > >> restored (according to logs) and vt_efifb_init() is being called but
> the
> > >> screen (laptop built in display) stays black. The system seems
> > >> operational otherwise. If I load i915kms again in this state I get
> back
> > >> a visible (i915kms) framebuffer.
> > >>
> > >> Did we ever have this working so it's known to work?
> > >
> > > Recently on the linux kernel mailing list:
> > >
> > > http://lkml.iu.edu/hypermail/linux/kernel/1903.1/01162.html
> > >
> > > > Of course, once native drivers like i915 or radeon take over, such a
> > > framebuffer is toast... [6]
> > >
> > > > [6]
> linux/drivers/gpu/drm/i915/i915_drv.c::i915_kick_out_firmware_fb()
> > > > linux/drivers/gpu/drm/radeon/radeon_drv.c::radeon_pci_probe()
> > >
> > > So it seems like efifb is not supposed to work after a driver has been
> > > loaded at least once.
> > >
> > >
> > Hmm, well the code is there to handle switching back to the boot time
> > fb. What I think is happening is that i915 powers off the displays at
> > unload and vt doesn't know how to power on (or that it should).
> >
>
>  That and if the display pipeline is de-configured or the resolution
> changed you cannot reset it to the original state.
>  Unloading drm modules is only useful for testing (and finding leaks).


Yeah a normal user would never unload it. Since I mostly ssh to my test
machines I think I’m fine personally with losing the display while
unloading.

Keyboard input still works though and at least it doesn’t crash anymore :)


>
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> --
> Emmanuel Vadot <manu_at_bidouilliste.com> <manu_at_freebsd.org>
>