Re: [PATCH v3 1/3] Kconfig : Remove HAS_IOMEM dependency for Graphics support

[Farhan Ali]

On 02/21/2018 07:11 AM, Christian Borntraeger wrote:
> On 02/21/2018 01:07 PM, Cornelia Huck wrote:
> [...]
> > > > But if you need to enable PCI to get IOMEM, I wonder why this patch here
> > > > is needed at all? The Graphics menu / VT dummy console should be
> > > > available in the config if IOMEM is enabled anyway?
> > >
> > > That is a good question. With CONFIG_PCI=y I can select virtio-gpu and dummy-console.
> > > IIRC the issue was that with patch 3 we can have the situation where we have
> > > CONFIG_VT = y and CONFIG_DUMMY_CONSOLE=n and this will crash early during boot as
> > > conswitchp is NULL.

Yes, VT layer initializes very early in the boot process and looks for a 
console. If it can't find any it will crash. I believe that was the 
whole point of having the dummy console.

> > So in practice, CONFIG_VT depends on "there's a console available, even
> > if it's only the dummy one"?
>
> Yes. Maybe we should simple move dummy_console outside of drivers/video/console/Kconfig
> into something that is always available.

I agree, but where should it go? consoles are kinda tightly tied to 
video/Graphics Support.

> > > This patches goal was to always enable dummy console even without
> > > PCI, but it obviously fails to do so.
This patch should enable the dummy console even without PCI but we won't 
have DRM/Virtio GPU.

> > OTOH, the dummy console really should not depend on anything, as it is
> > only doing dummy things.
> >
> > > So what about allowing CONFIG_VT on s390 only if we have PCI?
> > >
> > >
> > > diff --git a/drivers/tty/Kconfig b/drivers/tty/Kconfig
> > > index 84810075a6a0..1c7fe09d6f90 100644
> > > --- a/drivers/tty/Kconfig
> > > +++ b/drivers/tty/Kconfig
> > > @@ -11,7 +11,7 @@ if TTY
> > >   
> > >   config VT
> > >          bool "Virtual terminal" if EXPERT
> > > -       depends on !UML
> > > +       depends on !UML && (!S390 || PCI)
> > >          select INPUT
> > >          default y
> > >          ---help---
> >
> > Would cover your use case, but feels wrong to me... config dependencies
> > aren't fun :/