[Intel-xe] [PATCH 2/3] drm/xe: Add wrapper function for VGA decode setup

[Shankar, Uma]

> -----Original Message-----
> From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> Sent: Thursday, September 21, 2023 5:48 PM
> To: Shankar, Uma <uma.shankar at intel.com>
> Cc: Nikula, Jani <jani.nikula at intel.com>; intel-xe at lists.freedesktop.org; Borah,
> Chaitanya Kumar <chaitanya.kumar.borah at intel.com>
> Subject: Re: [PATCH 2/3] drm/xe: Add wrapper function for VGA decode setup
> 
> On Wed, Sep 20, 2023 at 12:39:19PM +0000, Shankar, Uma wrote:
> >
> >
> > > -----Original Message-----
> > > From: Nikula, Jani <jani.nikula at intel.com>
> > > Sent: Wednesday, September 20, 2023 3:38 PM
> > > To: Shankar, Uma <uma.shankar at intel.com>;
> > > intel-xe at lists.freedesktop.org
> > > Cc: Borah, Chaitanya Kumar <chaitanya.kumar.borah at intel.com>
> > > Subject: RE: [PATCH 2/3] drm/xe: Add wrapper function for VGA decode
> > > setup
> > >
> > > On Wed, 20 Sep 2023, "Shankar, Uma" <uma.shankar at intel.com> wrote:
> > > >> -----Original Message-----
> > > >> From: Nikula, Jani <jani.nikula at intel.com>
> > > >> Sent: Tuesday, September 19, 2023 4:00 PM
> > > >> To: Shankar, Uma <uma.shankar at intel.com>;
> > > >> intel-xe at lists.freedesktop.org
> > > >> Cc: Borah, Chaitanya Kumar <chaitanya.kumar.borah at intel.com>;
> > > >> Shankar, Uma <uma.shankar at intel.com>
> > > >> Subject: Re: [PATCH 2/3] drm/xe: Add wrapper function for VGA
> > > >> decode setup
> > > >>
> > > >> On Mon, 18 Sep 2023, Uma Shankar <uma.shankar at intel.com> wrote:
> > > >> > Some of the VGA functionality is not needed by the Intel Xe driver.
> > > >> > Adding a wrapper function for VGA decode setup.
> > > >> >
> > > >> > Signed-off-by: Uma Shankar <uma.shankar at intel.com>
> > > >> > ---
> > > >> >  drivers/gpu/drm/xe/display/ext/i915_utils.c | 5 +++++
> > > >> >  drivers/gpu/drm/xe/xe_display.h             | 1 +
> > > >> >  2 files changed, 6 insertions(+)
> > > >> >
> > > >> > diff --git a/drivers/gpu/drm/xe/display/ext/i915_utils.c
> > > >> > b/drivers/gpu/drm/xe/display/ext/i915_utils.c
> > > >> > index 981edc2788bc..aa3e9ad718c3 100644
> > > >> > --- a/drivers/gpu/drm/xe/display/ext/i915_utils.c
> > > >> > +++ b/drivers/gpu/drm/xe/display/ext/i915_utils.c
> > > >> > @@ -20,3 +20,8 @@ int __i915_inject_probe_error(struct
> > > >> > drm_i915_private *i915, int err,  {
> > > >> >     return 0;
> > > >> >  }
> > > >> > +
> > > >> > +unsigned int intel_gmch_vga_set_decode(struct pci_dev *pdev,
> > > >> > +bool
> > > >> > +enable_decode) {
> > > >> > +   return -EIO;
> > > >> > +}
> > > >>
> > > >> We don't really want to add anything new to i915_utils.c. It's
> > > >> just temporary cruft that had to be taken from i915 to make the rest
> compile.
> > > >
> > > > Hi Jani,
> > > > Thanks for the feedback.
> > > >
> > > > I was looking at any good place to stack it together. There are
> > > > some misc stuff like this which we may need for some other stuff as well.
> > > > Should I add a xe_disp_misc file for this or any other suggestion
> > > > on file which
> > > we can use.
> > >
> > > Let's take a step back, though.
> > >
> > > Why is this call needed on i915 but not on xe?
> >
> > Ideally it should be needed even here. Not sure on the exact usage
> > though, the GMCHGraphicsControl is there on current platforms as well. Trying
> to gather some info to get clarity.
> >
> > @ville.syrjala at linux.intel.com Do you know how critical this is or can
> > we defer its enabling and add support later directly in upstream.
> 
> That whole code is mostly nonsense since that register is normally locked by the
> BIOS. So despite what the code thinks it cannot realibly be used to enable/disable
> VGA decoding. I have some old branch somewhere that tries to use other means
> to control this, but IIRC for some reason I had to resort to stop_machine() to
> make it not suck in some way.

Thanks Ville for the inputs, so for Xe I guess we can just leave it out. We can try to fix this
in upstream directly.

Will try to add a new file xe_display_misc.c to keep these miscellaneous things together in
one file. @Nikula, Jani Hope this is ok.

Regards,
Uma Shankar

> --
> Ville Syrjälä
> Intel