Fix irq source-id error

[quo]

The IOMMU gives the following error when trying to use the irq:

DMAR: DRHD: handling fault status reg 2
DMAR: [INTR-REMAP] Request device [01:05.0] fault index 0x2f [fault reason 0x26] Blocked an interrupt request due to source-id verification failure

No clue how to fix this. May be an ACPI bug?

[quo]

It says 01:05.0, but the actual address of the THC is 00:10.6. I guess that's the problem? But I don't really know how any of this IOMMU stuff works. According to lspci there isn't even anything at 01:05.0...

Should probably compile a kernel with INTEL_IOMMU_DEBUGFS to get some more info.

[quo]

The source/request ID check is set up in the kernel by set_msi_sid(). This checks for DMA alias ids with pci_for_each_dma_alias(). As far as I can tell, the only ways you can have aliases are:

1. If the device is on a VMD bus (via pci_real_dma_dev()), which I don't think it is,
2. If an alias was set up with pci_add_dma_alias(), but this can only create aliases on the same bus, or
3. If the device is behind a PCI bridge, which I also don't think it is.

So since there are no aliases, set_msi_sid() creates a strict check for the 00:10.6 sid. And then for some reason the interrupt has request id 01:05.0.

We can't use a quirk to add an alias since the bus number differs. We can add a hack to set_msi_sid() to disable id checking for the THC device only (instead of just disabling it for all devices with intremap=nosid). We could also leave the check enabled, but hardcode the sid to 01:05.0 for THC, but since I don't understand where that value comes from, I don't know if the value might change.

Patch to disable the sid check for ITHC device only:

diff --git a/drivers/iommu/intel/irq_remapping.c b/drivers/iommu/intel/irq_remapping.c
index a67319597884..9f9322a17810 100644
--- a/drivers/iommu/intel/irq_remapping.c
+++ b/drivers/iommu/intel/irq_remapping.c
@@ -396,6 +396,22 @@ static int set_msi_sid(struct irte *irte, struct pci_dev *dev)
 	data.busmatch_count = 0;
 	pci_for_each_dma_alias(dev, set_msi_sid_cb, &data);
 
+	/*
+	 * The Intel Touch Host Controller is at 00:10.6, but for some reason
+	 * the MSI interrupts have request id 01:05.0.
+	 * Disable id verification to work around this.
+	 * FIXME Find proper fix or turn this into a quirk.
+	 */
+	if (dev->vendor == PCI_VENDOR_ID_INTEL && (dev->class >> 8) == PCI_CLASS_INPUT_PEN) {
+		switch(dev->device) {
+		case 0x98d0: case 0x98d1: // LKF
+		case 0xa0d0: case 0xa0d1: // TGL LP
+		case 0x43d0: case 0x43d1: // TGL H
+			set_irte_sid(irte, SVT_NO_VERIFY, SQ_ALL_16, 0);
+			return 0;
+		}
+	}
+
 	/*
 	 * DMA alias provides us with a PCI device and alias.  The only case
 	 * where the it will return an alias on a different bus than the

[Headcrabed]

Any news about this? Firmware seems to have upgraded since then, did acpi table changed?

[quo]

It looks like nosid is maybe no longer required for the new Alder Lake devices, so I suspect it was a hardware bug on Tiger Lake.

I don't know if something could be done on the ACPI side to fix/workaround the problem (I don't really know how ACPI interacts with the iommu).

I believe the above patch will be added to the Surface kernel, which will remove the need for using nosid with that kernel at least.

I think a proper fix will involve adding support to the kernel for DMA aliases with different bus numbers, then I could add an alias in the ithc driver. But someone who really understands how PCI MSI and the Intel iommu work should have a look at this.

Edit: I could also add some code to detect if the irq is working, and automatically switch to polling mode if it isn't. Not optimal, but maybe the easiest fix.