Bug 13721

Summary:	[TRIVIAL]DRM drivers don't use PCI DMA API.
Product:	Drivers	Reporter:	David Woodhouse (dwmw2)
Component:	Video(DRI - Intel)	Assignee:	intel-gfx-bugs (intel-gfx-bugs)
Status:	RESOLVED CODE_FIX
Severity:	normal	CC:	alan, chris, daniel, intel-gfx-bugs
Priority:	P1
Hardware:	All
OS:	Linux
Kernel Version:	3.4	Subsystem:
Regression:	No	Bisected commit-id:

Description David Woodhouse 2009-07-06 12:14:35 UTC

When the system has an IOMMU, it prevents all DMA from the graphics devices. See http://bugzilla.kernel.org/show_bug.cgi?id=11821#c16 for an example.

For the Intel IOMMU we have a temporary workaround for this brokenness, CONFIG_DMAR_BROKEN_GFX_WA. This kind of workaround apparently isn't easy to do for the AMD IOMMU though, and isn't necessarily the right answer even if it _was_ feasible.

We need to fix the drivers. I plan to remove CONFIG_DMAR_BROKEN_GFX_WA in 2.6.32.

Comment 1 Alan 2012-06-12 10:26:41 UTC

Option still present and still refers to the 2.6.32 removal in Kconfig - would you perhaps mind fixing Kconfig Dave 8)

Comment 2 David Woodhouse 2013-11-20 13:39:15 UTC

I think the Intel graphics drivers (which are the only ones for which DMAR_BROKEN_GFX_WA is applicable) are fixed now. Shame we still don't do any QA on the hardware before we ship it though...

Comment 3 Alan 2013-11-20 14:55:13 UTC

Moving to DRI/intel to check what needs to happen and who needs to own it

Comment 4 Chris Wilson 2013-11-20 15:08:32 UTC

We migrated over to dma_map_sg() and pci_map_page() and rely on intel_iommu to dtrt for the variety of broken VT-d/gfx, with the occasional quirk in the driver for when the GPU itself hangs if its iommu mapping is changed whilst it is busy.

Comment 5 Daniel Vetter 2013-11-20 15:28:54 UTC

Also due to too much hw breakage we won't ever be able to remove the workaround, at least as a kernel cmdline option in the form of intel_iommu=igfx_off. Too valuable for debugging.