linux-kernel - [RFC] iommu: Fix virtio-iommu probing

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Message-ID: <20250814141758.2140641-1-eric.auger@redhat.com>
Date: Thu, 14 Aug 2025 16:17:58 +0200
From: Eric Auger <eric.auger@...hat.com>
To: eric.auger.pro@...il.com,
	eric.auger@...hat.com,
	robin.murphy@....com,
	rafael@...nel.org,
	bhelgaas@...gle.com,
	jgg@...pe.ca,
	lpieralisi@...nel.org,
	linux-acpi@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	lenb@...nel.org,
	jean-philippe@...aro.org,
	jsnitsel@...hat.com
Subject: [RFC] iommu: Fix virtio-iommu probing

Commit bcb81ac6ae3c ("iommu: Get DT/ACPI parsing into the proper
probe path") broke virtio-iommu probing and no iommu group are
produced anymore.

When probe_iommu_group() gets called viommu_probe_device() fails
because viommu_get_by_fwnode(fwspec->iommu_fwnode) returns NULL.
So it seems we need to restore the original iommu_probe_device
call site in acpi_iommu_configure_id() to get a chance to probe
the device again.

Maybe this defeats the whole purpose of the original commit but
at least it fixes the virtio-iommu probing.

Fixes: bcb81ac6ae3c ("iommu: Get DT/ACPI parsing into the proper probe path")
Cc: stable@...r.kernel.org # v6.15+
Signed-off-by: Eric Auger <eric.auger@...hat.com>

---

I also tested smmu probing and this seems to work fine.
---
 drivers/acpi/scan.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
index fb1fe9f3b1a3..9f4efa8f75a6 100644
--- a/drivers/acpi/scan.c
+++ b/drivers/acpi/scan.c
@@ -1632,6 +1632,13 @@ static int acpi_iommu_configure_id(struct device *dev, const u32 *id_in)
 		err = viot_iommu_configure(dev);
 	mutex_unlock(&iommu_probe_device_lock);
 
+	/*
+	 * If we have reason to believe the IOMMU driver missed the initial
+	 * iommu_probe_device() call for dev, replay it to get things in order.
+	 */
+	if (!err && dev->bus)
+		err = iommu_probe_device(dev);
+
 	return err;
 }
 
-- 
2.49.0