iommu: Add quirk for Intel graphic devices in map_sg (65f746e8) · Commits · 戴 / test

Combining the sg segments exposes a bug in the Intel i915 driver which causes visual artifacts and the screen to freeze. This is most likely because of how the i915 handles the returned list. It probably doesn't respect the returned value specifying the number of elements in the list and instead depends on the previous behaviour of the Intel iommu driver which would return the same number of elements in the output list as in the input list. [ This has been fixed in the i915 tree, but we agreed to carry this fix temporarily in the iommu tree and revert it before 5.11 is released: https://lore.kernel.org/linux-iommu/20201103105442.GD22888@8bytes.org/ -- Will ] Signed-off-by:

Tom Murphy <murphyt7@tcd.ie> Signed-off-by:

Lu Baolu <baolu.lu@linux.intel.com> Tested-by:

Logan Gunthorpe <logang@deltatee.com> Link: https://lore.kernel.org/r/20201124082057.2614359-5-baolu.lu@linux.intel.com Signed-off-by:

Will Deacon <will@kernel.org>

drivers/iommu/dma-iommu.c

+27 −0

Original line number	Diff line number	Diff line
		@@ -878,6 +878,33 @@ static int __finalise_sg(struct device dev, struct scatterlist sg, int nents,
		unsigned int cur_len = 0, max_len = dma_get_max_seg_size(dev);
		int i, count = 0;

		/*
		* The Intel graphic driver is used to assume that the returned
		* sg list is not combound. This blocks the efforts of converting
		* Intel IOMMU driver to dma-iommu api's. Add this quirk to make the
		* device driver work and should be removed once it's fixed in i915
		* driver.
		*/
		if (IS_ENABLED(CONFIG_DRM_I915) && dev_is_pci(dev) &&
		to_pci_dev(dev)->vendor == PCI_VENDOR_ID_INTEL &&
		(to_pci_dev(dev)->class >> 16) == PCI_BASE_CLASS_DISPLAY) {
		for_each_sg(sg, s, nents, i) {
		unsigned int s_iova_off = sg_dma_address(s);
		unsigned int s_length = sg_dma_len(s);
		unsigned int s_iova_len = s->length;

		s->offset += s_iova_off;
		s->length = s_length;
		sg_dma_address(s) = dma_addr + s_iova_off;
		sg_dma_len(s) = s_length;
		dma_addr += s_iova_len;

		pr_info_once("sg combining disabled due to i915 driver\n");
		}

		return nents;
		}

		for_each_sg(sg, s, nents, i) {
		/* Restore this segment's original unaligned fields first */
		unsigned int s_iova_off = sg_dma_address(s);

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