[PATCH] drm/i915: prevent generating unusable gvt build which no mpt module is selected

[Du, Changbin]

Hi, Jani, just relized you are in i915 team. :)

> > +menu "Intel GVT-g graphics virtualization host support"
> > +	depends on DRM_I915
> > +	depends on 64BIT
> > +
> >  config DRM_I915_GVT
> > -        bool "Enable Intel GVT-g graphics virtualization host support"
> > -        depends on DRM_I915
> > -        depends on 64BIT
> > -        default n
> > -        help
> > +	bool "Enable Intel GVT-g graphics virtualization host support"
> > +	default n
> > +	depends on DRM_I915_GVT_KVMGT
> > +	help
> 
> With this change, you can't actually change this config option. It's
> purely subject to CONFIG_DRM_I915_GVT_KVMGT. You need to enable KVMGT to
> even see this option, but enabling it will enable this one too. You
> can't disable this before you disable KVMGT, but then disabling KVMGT
> will disable this one too. This config option becomes pointless as a
> visible option. Which isn't all that bad, considering
> Documentation/kbuild/kconfig-language.txt:
>
Jani, this is by design in this patch. We will add another xengt hypervisor glue
layer to support XenGT. After that, enable DRM_I915_GVT only if at least one of
KVMGT or XENGT enabled or both. Also it doesn't make sense that we only build
KVMGT/XenGT module without DRM_I915_GVT.

Such mechanism is not as straigforward as two simple 'choice', so I agree with
'choice' if you prefer it. As you said, it is not a big problem.

>   Note:
> 	select should be used with care. select will force
> 	a symbol to a value without visiting the dependencies.
> 	By abusing select you are able to select a symbol FOO even
> 	if FOO depends on BAR that is not set.
> 	In general use select only for non-visible symbols
> 	(no prompts anywhere) and for symbols with no dependencies.
> 	That will limit the usefulness but on the other hand avoid
> 	the illegal configurations all over.
> 
Yes, we should always be carefull with 'select' and should not use it if
possible. So here I must create a 'menu' to ensure its safety.

> BR,
> Jani.
> 
> >  	  Choose this option if you want to enable Intel GVT-g graphics
> >  	  virtualization technology host support with integrated graphics.
> >  	  With GVT-g, it's possible to have one integrated graphics
> > @@ -116,13 +119,14 @@ config DRM_I915_GVT
> >  
> >  config DRM_I915_GVT_KVMGT
> >  	tristate "Enable KVM/VFIO support for Intel GVT-g"
> > -	depends on DRM_I915_GVT
> > +	select DRM_I915_GVT
> >  	depends on KVM
> >  	depends on VFIO_MDEV && VFIO_MDEV_DEVICE
> >  	default n
> >  	help
> >  	  Choose this option if you want to enable KVMGT support for
> >  	  Intel GVT-g.
> > +endmenu
> >  
> >  menu "drm/i915 Debugging"
> >  depends on DRM_I915
> 
> -- 
> Jani Nikula, Intel Open Source Technology Center
> _______________________________________________
> intel-gvt-dev mailing list
> intel-gvt-dev at lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/intel-gvt-dev

-- 
Thanks,
Changbin Du
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