ba00196ca4
A kernel command called igfx_off was introduced in commit <ba39592764ed>
("Intel IOMMU: Intel IOMMU driver"). This command allows the user to
disable the IOMMU dedicated to SOC-integrated graphic devices.
Commit <9452618e7462> ("iommu/intel: disable DMAR for g4x integrated gfx")
used this mechanism to disable the graphic-dedicated IOMMU for some
problematic devices. Later, more problematic graphic devices were added
to the list by commit <1f76249cc3beb> ("iommu/vt-d: Declare Broadwell igfx
dmar support snafu").
On the other hand, commit <19943b0e30b05> ("intel-iommu: Unify hardware
and software passthrough support") uses the identity domain for graphic
devices if CONFIG_DMAR_BROKEN_GFX_WA is selected.
+ if (iommu_pass_through)
+ iommu_identity_mapping = 1;
+#ifdef CONFIG_DMAR_BROKEN_GFX_WA
+ else
+ iommu_identity_mapping = 2;
+#endif
...
static int iommu_should_identity_map(struct pci_dev *pdev, int startup)
{
+ if (iommu_identity_mapping == 2)
+ return IS_GFX_DEVICE(pdev);
...
In the following driver evolution, CONFIG_DMAR_BROKEN_GFX_WA and
quirk_iommu_igfx() are mixed together, causing confusion in the driver's
device_def_domain_type callback. On one hand, dmar_map_gfx is used to turn
off the graphic-dedicated IOMMU as a workaround for some buggy hardware;
on the other hand, for those graphic devices, IDENTITY mapping is required
for the IOMMU core.
Commit <4b8d18c0c986> "iommu/vt-d: Remove INTEL_IOMMU_BROKEN_GFX_WA" has
removed the CONFIG_DMAR_BROKEN_GFX_WA option, so the IDENTITY_DOMAIN
requirement for graphic devices is no longer needed. Therefore, this
requirement can be removed from device_def_domain_type() and igfx_off can
be made independent.
Fixes: 4b8d18c0c9 ("iommu/vt-d: Remove INTEL_IOMMU_BROKEN_GFX_WA")
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Link: https://lore.kernel.org/r/20240428032020.214616-1-baolu.lu@linux.intel.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.