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Date:   Tue, 22 Jan 2019 11:46:39 +0100
From:   Daniel Vetter <daniel@...ll.ch>
To:     Joerg Roedel <joro@...tes.org>
Cc:     Eric Wong <e@...24.org>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        David Woodhouse <dwmw2@...radead.org>,
        David Airlie <airlied@...ux.ie>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        "list@....net:IOMMU DRIVERS <iommu@...ts.linux-foundation.org>, Joerg
        Roedel <joro@...tes.org>," <iommu@...ts.linux-foundation.org>,
        intel-gfx <intel-gfx@...ts.freedesktop.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] iommu/intel: quirk to disable DMAR for QM57 igfx

On Tue, Jan 22, 2019 at 11:39 AM Joerg Roedel <joro@...tes.org> wrote:
>
> On Fri, Jan 18, 2019 at 12:17:05PM +0000, Eric Wong wrote:
> > @@ -5411,6 +5411,7 @@ DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, 0x2e20, quirk_iommu_g4x_gfx);
> >  DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, 0x2e30, quirk_iommu_g4x_gfx);
> >  DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, 0x2e40, quirk_iommu_g4x_gfx);
> >  DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, 0x2e90, quirk_iommu_g4x_gfx);
> > +DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, 0x0044, quirk_iommu_g4x_gfx);
> >
> >  static void quirk_iommu_rwbf(struct pci_dev *dev)
> >  {
> > @@ -5457,7 +5458,6 @@ static void quirk_calpella_no_shadow_gtt(struct pci_dev *dev)
> >         }
> >  }
> >  DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, 0x0040, quirk_calpella_no_shadow_gtt);
> > -DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, 0x0044, quirk_calpella_no_shadow_gtt);
> >  DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, 0x0062, quirk_calpella_no_shadow_gtt);
> >  DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, 0x006a, quirk_calpella_no_shadow_gtt);
>
> This seems to make sense to me. Joonas, any comments or objections?

This is ironlake, which has a huge iommu hack in the gpu driver to
work around hard hangs, which:
- causes massive stalls and kills performance
- isn't well tested (it's the only one that needs this), so tends to break

So if we do this then imo we should:
- probably nuke that w/a too (check for needs_idle_maps and all the
related stuff in i915_gem_gtt.c)
- roll it out for all affected chips (i.e. need to include 0x0040).

Note that the string of platforms which have various issues with iommu
and igfx is very long, thus far we only disabled it where there's no
workaround to stop it from hanging the box, but otherwise left it
enabled. So if we make a policy change to also disable it anywhere
where it doesn't work well (instead of not at all), there's a pile
more platforms to switch.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch

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