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

["Tian, Kevin" <kevin.tian@intel.com>]

> From: Ting-Wei Lan [mailto:lantw44@gmail.com]
> 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@gmail.com>
> ---
> 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. :-)

Thanks
Kevin