Re: [Xen-devel] [PATCH v2] VT-d: add iommu=igfx option to workaround graphics issues

[Ting-Wei Lan <lantw44@xxxxxxxxx>]

Tian, Kevin æ èå2015å07æ31æ 09:26 åé:
> > From: Ting-Wei Lan [mailto:lantw44@xxxxxxxxx]
> > Sent: Sunday, July 26, 2015 12:58 AM
> >
> > When using Linux >= 3.19 (commit 47591df) as dom0 on some Intel Ironlake
> > devices, It is possible to encounter graphics issues that make screen
> > unreadable or crash the system. It was reported in freedesktop bugzilla:
> >
> > https://bugs.freedesktop.org/show_bug.cgi?id=90037
> >
> > As we still cannot find a proper fix for this problem, this patch adds
> > iommu=igfx option to control whether Intel graphics IOMMU is enabled on
> > these devices. Running Xen with iommu=no-igfx is similar to running
> > Linux with intel_iommu=igfx_off, which disables IOMMU for Intel Ironlake
> > GPU. This can be used by users to manually workaround the problem before
> > a fix is available for i915 driver.
> >
> > Signed-off-by: Ting-Wei Lan <lantw44@xxxxxxxxx>
> > ---
> > Changed since v1:
> >    * Replace igfx_off with igfx
> >
> > This patch is currently only build-tested because I don't have access to
> > the hardware that have graphics issues this week. I will test this new
> > patch next week.
> >
> >   docs/misc/xen-command-line.markdown  | 12 +++++++++++-
> >   xen/drivers/passthrough/iommu.c      |  3 +++
> >   xen/drivers/passthrough/vtd/quirks.c |  2 +-
> >   xen/include/xen/iommu.h              |  2 +-
> >   4 files changed, 16 insertions(+), 3 deletions(-)
> >
> > diff --git a/docs/misc/xen-command-line.markdown
> > b/docs/misc/xen-command-line.markdown
> > index 13f03ad..6262be6 100644
> > --- a/docs/misc/xen-command-line.markdown
> > +++ b/docs/misc/xen-command-line.markdown
> > @@ -793,7 +793,7 @@ debug hypervisor only).
> >   > Default: `new` unless directed-EOI is supported
> >
> >   ### iommu
> > -> `= List of [ <boolean> | force | required | intremap | qinval | snoop | 
> > sharept |
> > dom0-passthrough | dom0-strict | amd-iommu-perdev-intremap | workaround_bios_bug
> > | verbose | debug ]`
> > +> `= List of [ <boolean> | force | required | intremap | qinval | snoop | 
> > sharept |
> > dom0-passthrough | dom0-strict | amd-iommu-perdev-intremap | workaround_bios_bug
> > | igfx | verbose | debug ]`
> >
> >   > Sub-options:
> >
> > @@ -867,6 +867,16 @@ debug hypervisor only).
> >   >> ignored (normally IOMMU setup fails if any of the devices listed by a DRHD
> >   >> entry aren't PCI discoverable).
> >
> > +> `igfx` (VT-d)
> > +
> > +> Default: `true`
> > +
> > +>> Enable IOMMU for Intel Calpella/Ironlake devices. This option does not
> > +>> affect grahpics IOMMU on other devices. The intended usage of this option
> > +>> is `no-igfx`, which is silimar to Linux `intel_iommu=igfx_off` option used
> > +>> to workaround graphics issues. If adding `no-igfx` fixes anything, you
> > +>> should file a bug reporting the problem.
> > +
> For above description let's make it general, i.e Enable IOMMU for Intel 
> Processor
> Graphics devices. You can list Calpella/Ironlake as the example, but not the 
> only
> target. :-)
no-igfx only works with Calpella/Ironlake because 
is_igd_vt_enabled_quirk() contains this code:
if ( !IS_ILK(ioh_id) )
    return 1;

The newly added variable iommu_igfx only changes the return value of 
is_igd_vt_enabled_quirk() when IS_ILK(ioh_id) is true. I don't know 
whether we will need no-igfx on other Intel graphics devices because I 
don't many devices to test and I don't have other devices that have this 
problem.
> Thanks
> Kevin

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