[PATCH] drm/i915: only disable default vga device

[Emil Velikov]

On Wed, 26 May 2021 at 17:21, Emil Velikov <emil.l.velikov at gmail.com> wrote:
>
> Hi Ville,
>
> On Tue, 18 May 2021 at 12:17, Ville Syrjälä
> <ville.syrjala at linux.intel.com> wrote:
> >
> > On Tue, May 18, 2021 at 12:09:56PM +0100, Emil Velikov wrote:
> > > Hi Ville,
> > >
> > > On Mon, 17 May 2021 at 18:24, Ville Syrjälä
> > > <ville.syrjala at linux.intel.com> wrote:
> > > >
> > > > On Sun, May 16, 2021 at 06:14:32PM +0100, Emil Velikov wrote:
> > > > > From: Vivek Das Mohapatra <vivek at collabora.com>
> > > > >
> > > > > This patch is to do with seamless handover, eg when the sequence is
> > > > > bootloader → plymouth → desktop.
> > > > >
> > > > > It switches the vga arbiter from the "other" GPU to the default one
> > > > > (intel in this case), so the driver can issue some io().
> > > >
> > > > I don't understand what this commit message is trying to say.
> > > >
> > > Bunch of context is lost due to the patch age, so I'm not 100% sure of
> > > the actual hardware setup where this occurs.
> > > Does the following make sense?
> > >
> > > Currently on dual GPU systems, we do not get seamless handover as the
> > > output flickers during the transition bootloader -> plymouth ->
> > > desktop.
> > > This happens as a result of switching (via the VGA arbiter) from the
> > > "other" GPU back to the default i915 one and issuing io() commands.
> >
> > Hmm. Does this work?
> >
> > --- a/drivers/gpu/drm/i915/display/intel_vga.c
> > +++ b/drivers/gpu/drm/i915/display/intel_vga.c
> > @@ -29,6 +29,9 @@ void intel_vga_disable(struct drm_i915_private *dev_priv)
> >         i915_reg_t vga_reg = intel_vga_cntrl_reg(dev_priv);
> >         u8 sr1;
> >
> > +       if (intel_de_read(dev_priv, vga_reg) & VGA_DISP_DISABLE)
> > +               return;
> > +
> >         /* WaEnableVGAAccessThroughIOPort:ctg,elk,ilk,snb,ivb,vlv,hsw */
> >         vga_get_uninterruptible(pdev, VGA_RSRC_LEGACY_IO);
> >         outb(SR01, VGA_SR_INDEX);
> >
> Was able to replicate the issue somewhat and the above does help quite a lot.
> Feel free to add my:
> Reviewed-by: Emil Velikov <emil.velikov at collabora.com>
> Tested-by: Emil Velikov <emil.velikov at collabora.com>
>
Humble poke.

Cannot see this patch in the drm-misc or drm-intel trees. Is there
anything I do to help move it forward?

Thanks
-Emil