[Intel-gfx] [PATCH] drm/i915: Setting pch_id for Gen7.5+ in virtual environment

[Zhang, Xiong Y]

> On Wed, Mar 29, 2017 at 05:02:47PM +0800, Xiong Zhang wrote:
> > In a virtual passthrough environment, the ISA bridge isn't able to
> > be passed through. So pch_id couldn't be gotten from ISA bridge, but
> > pch_id is used to identify LPT_H and LPT_LP, this patch set pch_id
> > according to IGD type.
> >
> > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=99938
> >
> > Signed-off-by: Xiong Zhang <xiong.y.zhang at intel.com>
> > ---
> >  drivers/gpu/drm/i915/i915_drv.c | 8 ++++++++
> >  1 file changed, 8 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/i915/i915_drv.c
> b/drivers/gpu/drm/i915/i915_drv.c
> > index 8b807a9..32a9bff 100644
> > --- a/drivers/gpu/drm/i915/i915_drv.c
> > +++ b/drivers/gpu/drm/i915/i915_drv.c
> > @@ -135,9 +135,17 @@ static enum intel_pch intel_virt_detect_pch(struct
> drm_i915_private *dev_priv)
> >  		DRM_DEBUG_KMS("Assuming CouarPoint PCH\n");
> >  	} else if (IS_HASWELL(dev_priv) || IS_BROADWELL(dev_priv)) {
> >  		ret = PCH_LPT;
> > +		if (IS_HSW_ULT(dev_priv) || IS_BDW_ULT(dev_priv))
> > +			dev_priv->pch_id = INTEL_PCH_LPT_LP_DEVICE_ID_TYPE;
> > +		else
> > +			dev_priv->pch_id = INTEL_PCH_LPT_DEVICE_ID_TYPE;
> >  		DRM_DEBUG_KMS("Assuming LynxPoint PCH\n");
> >  	} else if (IS_SKYLAKE(dev_priv) || IS_KABYLAKE(dev_priv)) {
> >  		ret = PCH_SPT;
> > +		if (IS_SKL_ULT(dev_priv) || IS_KBL_ULT(dev_priv))
> > +			dev_priv->pch_id = INTEL_PCH_SPT_LP_DEVICE_ID_TYPE;
> > +		else
> > +			dev_priv->pch_id = INTEL_PCH_SPT_DEVICE_ID_TYPE;
> 
> I'm not 100% sure the ULT/ULX <=> LP thing always holds. I *think* it
> should but I've never been able to convince myself totally.
[Zhang, Xiong Y] For BDW ULT/ULX, it should be LP. A picture from https://gfxspecs.intel.com/Predator/Home/Index/4216 could confirm this.
For HSW ULT/ULX, I couldn't find a material to confirm this.
Anyway I copy this condition from the WARN_ON() in intel_detect_pch() 

For SKL/KBL ULT/ULX, I couldn't find a material to confirm this neither.

> As far as KBL goes, maybe we want PCH_KBP for it? Although I don't actually
> know why we even make the distinction between the two since they seem
> identical for us, and we don't distinguish LPT vs. WPT either. Rodrigo?
[Zhang, Xiong Y] For PCH_KBP, I couldn't find out which KBL type will co-work with it.
As the real ISA Bridge doesn't exist in a emulated guest machine, we couldn't get the real and accurate pch_id in guest. In such passthrough virtual environment, the only real HW is IGD which is passed through to guest, we could only assume the pch_id from this IGD.
Fortunately pch_id is only used to identify LPT_LP and LPT_H currently.
Without this patch, pch_id is totally wrong. And on LPT_LP platform without this patch, the local HDMI/DP display couldn't lightup when guest boot up. But this patch could only remedy part of pch_id. Currently I have two plans to improve this patch:
1) only remain pch_id assuming for HSW and BDW, as this is really we need to fix the bug.
  Delete pch_id assuming for SKL and KBL, as currently i915 driver don't use it.
2) Claim this patch's limitation in commit message.
Any suggestion ?
> >  		DRM_DEBUG_KMS("Assuming SunrisePoint PCH\n");
> >  	}
> >
> > --
> > 1.9.1
> >
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> 
> --
> Ville Syrjälä
> Intel OTC