The ACPI Virtual I/O Translation Table describes topology of
para-virtual platforms, similarly to vendor tables DMAR, IVRS and IORT.
For now it describes the relation between virtio-iommu and the endpoints
it manages.

Three steps are needed to configure DMA of endpoints:

(1) acpi_viot_init(): parse the VIOT table, find or create the fwnode
    associated to each vIOMMU device.

(2) When probing the vIOMMU device, the driver registers its IOMMU ops
    within the IOMMU subsystem. This step doesn't require any
    intervention from the VIOT driver.

(3) viot_iommu_configure(): before binding the endpoint to a driver,
    find the associated IOMMU ops. Register them, along with the
    endpoint ID, into the device's iommu_fwspec.

If step (3) happens before step (2), it is deferred until the IOMMU is
initialized, then retried.

Signed-off-by: Jean-Philippe Brucker <redacted>
---
 drivers/acpi/Kconfig      |   3 +
 drivers/iommu/Kconfig     |   1 +
 drivers/acpi/Makefile     |   2 +
 include/linux/acpi_viot.h |  19 +++
 drivers/acpi/bus.c        |   2 +
 drivers/acpi/scan.c       |   3 +
 drivers/acpi/viot.c       | 350 ++++++++++++++++++++++++++++++++++++++
 MAINTAINERS               |   8 +
 8 files changed, 388 insertions(+)
 create mode 100644 include/linux/acpi_viot.h
 create mode 100644 drivers/acpi/viot.c

diff --git a/drivers/acpi/Kconfig b/drivers/acpi/Kconfig
index eedec61e3476..3758c6940ed7 100644
--- a/drivers/acpi/Kconfig
+++ b/drivers/acpi/Kconfig

@@ -526,6 +526,9 @@ endif

 source "drivers/acpi/pmic/Kconfig"

+config ACPI_VIOT
+       bool
+
 endif  # ACPI

 config X86_PM_TIMER

diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
index 1f111b399bca..aff8a4830dd1 100644
--- a/drivers/iommu/Kconfig
+++ b/drivers/iommu/Kconfig

@@ -403,6 +403,7 @@ config VIRTIO_IOMMU
        depends on ARM64
        select IOMMU_API
        select INTERVAL_TREE
+       select ACPI_VIOT if ACPI
        help
          Para-virtualised IOMMU driver with virtio.

diff --git a/drivers/acpi/Makefile b/drivers/acpi/Makefile
index 700b41adf2db..a6e644c48987 100644
--- a/drivers/acpi/Makefile
+++ b/drivers/acpi/Makefile

@@ -118,3 +118,5 @@ video-objs                  += acpi_video.o video_detect.o
 obj-y                          += dptf/

 obj-$(CONFIG_ARM64)            += arm64/
+
+obj-$(CONFIG_ACPI_VIOT)                += viot.o

diff --git a/include/linux/acpi_viot.h b/include/linux/acpi_viot.h
new file mode 100644
index 000000000000..1eb8ee5b0e5f
--- /dev/null
+++ b/include/linux/acpi_viot.h

@@ -0,0 +1,19 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#ifndef __ACPI_VIOT_H__
+#define __ACPI_VIOT_H__
+
+#include <linux/acpi.h>
+
+#ifdef CONFIG_ACPI_VIOT
+void __init acpi_viot_init(void);
+int viot_iommu_configure(struct device *dev);
+#else
+static inline void acpi_viot_init(void) {}
+static inline int viot_iommu_configure(struct device *dev)
+{
+       return -ENODEV;
+}
+#endif
+
+#endif /* __ACPI_VIOT_H__ */

diff --git a/drivers/acpi/bus.c b/drivers/acpi/bus.c
index be7da23fad76..b835ca702ff0 100644
--- a/drivers/acpi/bus.c
+++ b/drivers/acpi/bus.c

@@ -27,6 +27,7 @@
 #include <linux/dmi.h>
 #endif
 #include <linux/acpi_iort.h>
+#include <linux/acpi_viot.h>
 #include <linux/pci.h>
 #include <acpi/apei.h>
 #include <linux/suspend.h>

@@ -1339,6 +1340,7 @@ static int __init acpi_init(void)
        pci_mmcfg_late_init();
        acpi_iort_init();
        acpi_scan_init();
+       acpi_viot_init();
        acpi_ec_init();
        acpi_debugfs_init();
        acpi_sleep_proc_init();

diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
index 5924421075f6..4db43c822ee7 100644
--- a/drivers/acpi/scan.c
+++ b/drivers/acpi/scan.c

@@ -9,6 +9,7 @@
 #include <linux/kernel.h>
 #include <linux/acpi.h>
 #include <linux/acpi_iort.h>
+#include <linux/acpi_viot.h>
 #include <linux/iommu.h>
 #include <linux/signal.h>
 #include <linux/kthread.h>

@@ -1554,6 +1555,8 @@ static const struct iommu_ops *acpi_iommu_configure_id(struct device *dev,
                return ops;

        err = iort_iommu_configure_id(dev, id_in);
+       if (err && err != -EPROBE_DEFER)
+               err = viot_iommu_configure(dev);

        /*
         * If we have reason to believe the IOMMU driver missed the initial

diff --git a/drivers/acpi/viot.c b/drivers/acpi/viot.c
new file mode 100644
index 000000000000..710e5a5eac70
--- /dev/null
+++ b/drivers/acpi/viot.c

@@ -0,0 +1,350 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Virtual I/O topology