[PATCH] ACPI: VIOT: Fix ACS setup

[Eric Auger <eric.auger@redhat.com>]

Currently acpi_viot_init() gets called after the pci
device has been scanned and pci_enable_acs() has been called.
So pci_request_acs() fails to be taken into account leading
to wrong single iommu group topologies when dealing with
multi-function root ports for instance.

We cannot simply move the acpi_viot_init() earlier, similarly
as the IORT init because the VIOT parsing relies on the pci
scan. However we can detect VIOT is present earlier and in
such a case, request ACS. Introduce a new acpi_viot_early_init()
routine that allows to call pci_request_acs() before the scan.

Fixes: 3cf485540e7b ("ACPI: Add driver for the VIOT table")
Signed-off-by: Eric Auger <eric.auger@redhat.com>
Reported-by: Jin Liu <jinl@redhat.com>
---
 drivers/acpi/bus.c        |  1 +
 drivers/acpi/viot.c       | 23 +++++++++++++++++------
 include/linux/acpi_viot.h |  2 ++
 3 files changed, 20 insertions(+), 6 deletions(-)

diff --git a/drivers/acpi/bus.c b/drivers/acpi/bus.c
index 86fa61a21826..906ad8153fd9 100644
--- a/drivers/acpi/bus.c
+++ b/drivers/acpi/bus.c
@@ -1400,6 +1400,7 @@ static int __init acpi_init(void)
 
 	pci_mmcfg_late_init();
 	acpi_iort_init();
+	acpi_viot_early_init();
 	acpi_hest_init();
 	acpi_ghes_init();
 	acpi_scan_init();
diff --git a/drivers/acpi/viot.c b/drivers/acpi/viot.c
index d2256326c73a..3c1be123e4d6 100644
--- a/drivers/acpi/viot.c
+++ b/drivers/acpi/viot.c
@@ -248,6 +248,23 @@ static int __init viot_parse_node(const struct acpi_viot_header *hdr)
 	return ret;
 }
 
+/**
+ * acpi_viot_early_init - Test the presence of VIOT and enable ACS
+ *
+ * If the VIOT does exist, ACS must be enabled. This cannot be
+ * done in acpi_viot_init() which is called after the bus scan
+ */
+void __init acpi_viot_early_init(void)
+{
+	acpi_status status;
+	struct acpi_table_header *hdr;
+
+	status = acpi_get_table(ACPI_SIG_VIOT, 0, &hdr);
+	if (!ACPI_FAILURE(status))
+		pci_request_acs();
+	acpi_put_table(hdr);
+}
+
 /**
  * acpi_viot_init - Parse the VIOT table
  *
@@ -319,12 +336,6 @@ static int viot_pci_dev_iommu_init(struct pci_dev *pdev, u16 dev_id, void *data)
 			epid = ((domain_nr - ep->segment_start) << 16) +
 				dev_id - ep->bdf_start + ep->endpoint_id;
 
-			/*
-			 * If we found a PCI range managed by the viommu, we're
-			 * the one that has to request ACS.
-			 */
-			pci_request_acs();
-
 			return viot_dev_iommu_init(&pdev->dev, ep->viommu,
 						   epid);
 		}
diff --git a/include/linux/acpi_viot.h b/include/linux/acpi_viot.h
index 1eb8ee5b0e5f..e58d60f8ff2e 100644
--- a/include/linux/acpi_viot.h
+++ b/include/linux/acpi_viot.h
@@ -6,10 +6,12 @@
 #include <linux/acpi.h>
 
 #ifdef CONFIG_ACPI_VIOT
+void __init acpi_viot_early_init(void);
 void __init acpi_viot_init(void);
 int viot_iommu_configure(struct device *dev);
 #else
 static inline void acpi_viot_init(void) {}
+static inline void acpi_viot_early_init(void) {}
 static inline int viot_iommu_configure(struct device *dev)
 {
 	return -ENODEV;
-- 
2.35.3