diff mbox

[V10,1/8] ACPI: I/O Remapping Table (IORT) initial support

Message ID 1473152938-17388-2-git-send-email-tn@semihalf.com (mailing list archive)
State New, archived
Delegated to: Bjorn Helgaas
Headers show

Commit Message

Tomasz Nowicki Sept. 6, 2016, 9:08 a.m. UTC 
IORT shows representation of IO topology for ARM based systems.
It describes how various components are connected together on
parent-child basis e.g. PCI RC -> SMMU -> ITS. Also see IORT spec.
http://infocenter.arm.com/help/topic/com.arm.doc.den0049b/DEN0049B_IO_Remapping_Table.pdf

Initial support allows to detect IORT table presence and save its
root pointer obtained through acpi_get_table(). The pointer validity
depends on acpi_gbl_permanent_mmap because if acpi_gbl_permanent_mmap
is not set while using IORT nodes we would dereference unmapped pointers.

For the aforementioned reason call iort_table_detect() from acpi_init()
which guarantees acpi_gbl_permanent_mmap to be set at that point.

Add generic helpers which are helpful for scanning and retrieving
information from IORT table content. List of the most important helpers:
- iort_find_dev_node() finds IORT node for a given device
- iort_node_map_rid() maps device RID and returns IORT node which provides
  final translation

IORT support is placed under drivers/acpi/arm64/ new directory due to its
ARM64 specific nature. The code there is considered only for ARM64.
The long term plan is to keep all ARM64 specific tables support
in this place e.g. GTDT table.

Signed-off-by: Tomasz Nowicki <tn@semihalf.com>
Reviewed-by: Hanjun Guo <hanjun.guo@linaro.org>
Reviewed-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
---
 drivers/acpi/Kconfig        |   4 +
 drivers/acpi/Makefile       |   2 +
 drivers/acpi/arm64/Kconfig  |   6 ++
 drivers/acpi/arm64/Makefile |   1 +
 drivers/acpi/arm64/iort.c   | 219 ++++++++++++++++++++++++++++++++++++++++++++
 drivers/acpi/bus.c          |   2 +
 include/linux/acpi_iort.h   |  30 ++++++
 7 files changed, 264 insertions(+)
 create mode 100644 drivers/acpi/arm64/Kconfig
 create mode 100644 drivers/acpi/arm64/Makefile
 create mode 100644 drivers/acpi/arm64/iort.c
 create mode 100644 include/linux/acpi_iort.h

Comments

Dennis Chen Sept. 9, 2016, 3:09 a.m. UTC | #1 
Hi Tomasz,

On Tue, Sep 06, 2016 at 11:08:51AM +0200, Tomasz Nowicki wrote:
[...]
> +static int iort_id_map(struct acpi_iort_id_mapping *map, u8 type, u32 rid_in,
> +		       u32 *rid_out)
> +{
> +	/* Single mapping does not care for input id */
> +	if (map->flags & ACPI_IORT_ID_SINGLE_MAPPING) {
> +		if (type == ACPI_IORT_NODE_NAMED_COMPONENT ||
> +		    type == ACPI_IORT_NODE_PCI_ROOT_COMPLEX) {
> +			*rid_out = map->output_base;
> +			return 0;
> +		}
> +
> +		pr_warn(FW_BUG "[map %p] SINGLE MAPPING flag not allowed for node type %d, skipping ID map\n",
> +			map, type);
> +		return -ENXIO;
> +	}
> +
> +	if (rid_in < map->input_base ||
> +	    (rid_in >= map->input_base + map->id_count))
> +		return -ENXIO;
> +
> +	*rid_out = map->output_base + (rid_in - map->input_base);
> +	return 0;
> +}
> +
> +static struct acpi_iort_node *iort_node_map_rid(struct acpi_iort_node *node,
> +						u32 rid_in, u32 *rid_out,
> +						u8 type)
> +{
> +	u32 rid = rid_in;
> +
> +	/* Parse the ID mapping tree to find specified node type */
> +	while (node) {
> +		struct acpi_iort_id_mapping *map;
> +		int i;
> +
> +		if (node->type == type) {
> +			if (rid_out)
> +				*rid_out = rid;
> +			return node;
> +		}
> +
> +		if (!node->mapping_offset || !node->mapping_count)
> +			goto fail_map;
If node->mapping_count is zero, then node->mapping_offset must be zero. A firmware bug
otherwise?
> +
> +		map = ACPI_ADD_PTR(struct acpi_iort_id_mapping, node,
> +				   node->mapping_offset);
> +
> +		/* Firmware bug! */
> +		if (!map->output_reference) {
> +			pr_err(FW_BUG "[node %p type %d] ID map has NULL parent reference\n",
> +			       node, node->type);
> +			goto fail_map;
> +		}
> +
> +		/* Do the RID translation */
> +		for (i = 0; i < node->mapping_count; i++, map++) {
> +			if (!iort_id_map(map, node->type, rid, &rid))
> +				break;
> +		}
>
Just curious about if there is kind of possibility that we can get some reduplicated DeviceIDs
with a deliberate ID mapping design in FW for the SMMU/RC node. For instance, for a system with 2
PCIe RCs both behind an individual SMMU device, how to make sure the StreamID mapped is unique 
across the entire system, the same for DeviceID mapped. 
Anyway, this is my personal confusion, maybe it's not a problem at all for current design ;-)

Thanks,
Dennis
> +
> +		if (i == node->mapping_count)
> +			goto fail_map;
> +
> +		node = ACPI_ADD_PTR(struct acpi_iort_node, iort_table,
> +				    map->output_reference);
> +	}
> +
> +fail_map:
> +	/* Map input RID to output RID unchanged on mapping failure*/
> +	if (rid_out)
> +		*rid_out = rid_in;
> +
> +	return NULL;
> +}
> +
> +static struct acpi_iort_node *iort_find_dev_node(struct device *dev)
> +{
> +	struct pci_bus *pbus;
> +
> +	if (!dev_is_pci(dev))
> +		return iort_scan_node(ACPI_IORT_NODE_NAMED_COMPONENT,
> +				      iort_match_node_callback, dev);
> +
> +	/* Find a PCI root bus */
> +	pbus = to_pci_dev(dev)->bus;
> +	while (!pci_is_root_bus(pbus))
> +		pbus = pbus->parent;
> +
> +	return iort_scan_node(ACPI_IORT_NODE_PCI_ROOT_COMPLEX,
> +			      iort_match_node_callback, &pbus->dev);
> +}
> +
> +void __init acpi_iort_init(void)
> +{
> +	acpi_status status;
> +
> +	status = acpi_get_table(ACPI_SIG_IORT, 0, &iort_table);
> +	if (ACPI_FAILURE(status) && status != AE_NOT_FOUND) {
> +		const char *msg = acpi_format_exception(status);
> +		pr_err("Failed to get table, %s\n", msg);
> +	}
> +}
> diff --git a/drivers/acpi/bus.c b/drivers/acpi/bus.c
> index 85b7d07..e56e643 100644
> --- a/drivers/acpi/bus.c
> +++ b/drivers/acpi/bus.c
> @@ -36,6 +36,7 @@
>  #ifdef CONFIG_X86
>  #include <asm/mpspec.h>
>  #endif
> +#include <linux/acpi_iort.h>
>  #include <linux/pci.h>
>  #include <acpi/apei.h>
>  #include <linux/dmi.h>
> @@ -1186,6 +1187,7 @@ static int __init acpi_init(void)
>  	}
>  
>  	pci_mmcfg_late_init();
> +	acpi_iort_init();
>  	acpi_scan_init();
>  	acpi_ec_init();
>  	acpi_debugfs_init();
> diff --git a/include/linux/acpi_iort.h b/include/linux/acpi_iort.h
> new file mode 100644
> index 0000000..fcacaf7
> --- /dev/null
> +++ b/include/linux/acpi_iort.h
> @@ -0,0 +1,30 @@
> +/*
> + * Copyright (C) 2016, Semihalf
> + *	Author: Tomasz Nowicki <tn@semihalf.com>
> + *
> + * This program is free software; you can redistribute it and/or modify it
> + * under the terms and conditions of the GNU General Public License,
> + * version 2, as published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope it will be useful, but WITHOUT
> + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
> + * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
> + * more details.
> + *
> + * You should have received a copy of the GNU General Public License along with
> + * this program; if not, write to the Free Software Foundation, Inc., 59 Temple
> + * Place - Suite 330, Boston, MA 02111-1307 USA.
> + */
> +
> +#ifndef __ACPI_IORT_H__
> +#define __ACPI_IORT_H__
> +
> +#include <linux/acpi.h>
> +
> +#ifdef CONFIG_ACPI_IORT
> +void acpi_iort_init(void);
> +#else
> +static inline void acpi_iort_init(void) { }
> +#endif
> +
> +#endif /* __ACPI_IORT_H__ */
> -- 
> 1.9.1
> 
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Lorenzo Pieralisi Sept. 9, 2016, 8:45 a.m. UTC | #2 
On Fri, Sep 09, 2016 at 11:09:40AM +0800, Dennis Chen wrote:
> Hi Tomasz,
> 
> On Tue, Sep 06, 2016 at 11:08:51AM +0200, Tomasz Nowicki wrote:
> [...]
> > +static int iort_id_map(struct acpi_iort_id_mapping *map, u8 type, u32 rid_in,
> > +		       u32 *rid_out)
> > +{
> > +	/* Single mapping does not care for input id */
> > +	if (map->flags & ACPI_IORT_ID_SINGLE_MAPPING) {
> > +		if (type == ACPI_IORT_NODE_NAMED_COMPONENT ||
> > +		    type == ACPI_IORT_NODE_PCI_ROOT_COMPLEX) {
> > +			*rid_out = map->output_base;
> > +			return 0;
> > +		}
> > +
> > +		pr_warn(FW_BUG "[map %p] SINGLE MAPPING flag not allowed for node type %d, skipping ID map\n",
> > +			map, type);
> > +		return -ENXIO;
> > +	}
> > +
> > +	if (rid_in < map->input_base ||
> > +	    (rid_in >= map->input_base + map->id_count))
> > +		return -ENXIO;
> > +
> > +	*rid_out = map->output_base + (rid_in - map->input_base);
> > +	return 0;
> > +}
> > +
> > +static struct acpi_iort_node *iort_node_map_rid(struct acpi_iort_node *node,
> > +						u32 rid_in, u32 *rid_out,
> > +						u8 type)
> > +{
> > +	u32 rid = rid_in;
> > +
> > +	/* Parse the ID mapping tree to find specified node type */
> > +	while (node) {
> > +		struct acpi_iort_id_mapping *map;
> > +		int i;
> > +
> > +		if (node->type == type) {
> > +			if (rid_out)
> > +				*rid_out = rid;
> > +			return node;
> > +		}
> > +
> > +		if (!node->mapping_offset || !node->mapping_count)
> > +			goto fail_map;
> If node->mapping_count is zero, then node->mapping_offset must be zero. A firmware bug
> otherwise?

So ? This function is there to map RIDs, not to validate all firmware
permutations and current code behaviour seems correct to me.

> > +
> > +		map = ACPI_ADD_PTR(struct acpi_iort_id_mapping, node,
> > +				   node->mapping_offset);
> > +
> > +		/* Firmware bug! */
> > +		if (!map->output_reference) {
> > +			pr_err(FW_BUG "[node %p type %d] ID map has NULL parent reference\n",
> > +			       node, node->type);
> > +			goto fail_map;
> > +		}
> > +
> > +		/* Do the RID translation */
> > +		for (i = 0; i < node->mapping_count; i++, map++) {
> > +			if (!iort_id_map(map, node->type, rid, &rid))
> > +				break;
> > +		}
> >
> Just curious about if there is kind of possibility that we can get
> some reduplicated DeviceIDs with a deliberate ID mapping design in FW
> for the SMMU/RC node. For instance, for a system with 2 PCIe RCs both
> behind an individual SMMU device, how to make sure the StreamID mapped
> is unique across the entire system, the same for DeviceID mapped.
> Anyway, this is my personal confusion, maybe it's not a problem at all
> for current design ;-)

Are you asking if FW can contain bugs ? Yes it can. I do not see
how your comment is related to this patch though.

Lorenzo

> Thanks,
> Dennis
> > +
> > +		if (i == node->mapping_count)
> > +			goto fail_map;
> > +
> > +		node = ACPI_ADD_PTR(struct acpi_iort_node, iort_table,
> > +				    map->output_reference);
> > +	}
> > +
> > +fail_map:
> > +	/* Map input RID to output RID unchanged on mapping failure*/
> > +	if (rid_out)
> > +		*rid_out = rid_in;
> > +
> > +	return NULL;
> > +}
> > +
> > +static struct acpi_iort_node *iort_find_dev_node(struct device *dev)
> > +{
> > +	struct pci_bus *pbus;
> > +
> > +	if (!dev_is_pci(dev))
> > +		return iort_scan_node(ACPI_IORT_NODE_NAMED_COMPONENT,
> > +				      iort_match_node_callback, dev);
> > +
> > +	/* Find a PCI root bus */
> > +	pbus = to_pci_dev(dev)->bus;
> > +	while (!pci_is_root_bus(pbus))
> > +		pbus = pbus->parent;
> > +
> > +	return iort_scan_node(ACPI_IORT_NODE_PCI_ROOT_COMPLEX,
> > +			      iort_match_node_callback, &pbus->dev);
> > +}
> > +
> > +void __init acpi_iort_init(void)
> > +{
> > +	acpi_status status;
> > +
> > +	status = acpi_get_table(ACPI_SIG_IORT, 0, &iort_table);
> > +	if (ACPI_FAILURE(status) && status != AE_NOT_FOUND) {
> > +		const char *msg = acpi_format_exception(status);
> > +		pr_err("Failed to get table, %s\n", msg);
> > +	}
> > +}
> > diff --git a/drivers/acpi/bus.c b/drivers/acpi/bus.c
> > index 85b7d07..e56e643 100644
> > --- a/drivers/acpi/bus.c
> > +++ b/drivers/acpi/bus.c
> > @@ -36,6 +36,7 @@
> >  #ifdef CONFIG_X86
> >  #include <asm/mpspec.h>
> >  #endif
> > +#include <linux/acpi_iort.h>
> >  #include <linux/pci.h>
> >  #include <acpi/apei.h>
> >  #include <linux/dmi.h>
> > @@ -1186,6 +1187,7 @@ static int __init acpi_init(void)
> >  	}
> >  
> >  	pci_mmcfg_late_init();
> > +	acpi_iort_init();
> >  	acpi_scan_init();
> >  	acpi_ec_init();
> >  	acpi_debugfs_init();
> > diff --git a/include/linux/acpi_iort.h b/include/linux/acpi_iort.h
> > new file mode 100644
> > index 0000000..fcacaf7
> > --- /dev/null
> > +++ b/include/linux/acpi_iort.h
> > @@ -0,0 +1,30 @@
> > +/*
> > + * Copyright (C) 2016, Semihalf
> > + *	Author: Tomasz Nowicki <tn@semihalf.com>
> > + *
> > + * This program is free software; you can redistribute it and/or modify it
> > + * under the terms and conditions of the GNU General Public License,
> > + * version 2, as published by the Free Software Foundation.
> > + *
> > + * This program is distributed in the hope it will be useful, but WITHOUT
> > + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
> > + * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
> > + * more details.
> > + *
> > + * You should have received a copy of the GNU General Public License along with
> > + * this program; if not, write to the Free Software Foundation, Inc., 59 Temple
> > + * Place - Suite 330, Boston, MA 02111-1307 USA.
> > + */
> > +
> > +#ifndef __ACPI_IORT_H__
> > +#define __ACPI_IORT_H__
> > +
> > +#include <linux/acpi.h>
> > +
> > +#ifdef CONFIG_ACPI_IORT
> > +void acpi_iort_init(void);
> > +#else
> > +static inline void acpi_iort_init(void) { }
> > +#endif
> > +
> > +#endif /* __ACPI_IORT_H__ */
> > -- 
> > 1.9.1
> > 
> > --
> > To unsubscribe from this list: send the line "unsubscribe linux-pci" in
> > the body of a message to majordomo@vger.kernel.org
> > More majordomo info at  http://vger.kernel.org/majordomo-info.html
> > 
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diff mbox

Patch

diff --git a/drivers/acpi/Kconfig b/drivers/acpi/Kconfig
index 445ce28..d5c0614 100644
--- a/drivers/acpi/Kconfig
+++ b/drivers/acpi/Kconfig
@@ -521,4 +521,8 @@  config ACPI_CONFIGFS
 	  userspace. The configurable ACPI groups will be visible under
 	  /config/acpi, assuming configfs is mounted under /config.
 
+if ARM64
+source "drivers/acpi/arm64/Kconfig"
+endif
+
 endif	# ACPI
diff --git a/drivers/acpi/Makefile b/drivers/acpi/Makefile
index 5ae9d85..e5ada78 100644
--- a/drivers/acpi/Makefile
+++ b/drivers/acpi/Makefile
@@ -105,3 +105,5 @@  obj-$(CONFIG_ACPI_CONFIGFS)	+= acpi_configfs.o
 
 video-objs			+= acpi_video.o video_detect.o
 obj-y				+= dptf/
+
+obj-$(CONFIG_ARM64)		+= arm64/
diff --git a/drivers/acpi/arm64/Kconfig b/drivers/acpi/arm64/Kconfig
new file mode 100644
index 0000000..4616da4
--- /dev/null
+++ b/drivers/acpi/arm64/Kconfig
@@ -0,0 +1,6 @@ 
+#
+# ACPI Configuration for ARM64
+#
+
+config ACPI_IORT
+	bool
diff --git a/drivers/acpi/arm64/Makefile b/drivers/acpi/arm64/Makefile
new file mode 100644
index 0000000..72331f2
--- /dev/null
+++ b/drivers/acpi/arm64/Makefile
@@ -0,0 +1 @@ 
+obj-$(CONFIG_ACPI_IORT) 	+= iort.o
diff --git a/drivers/acpi/arm64/iort.c b/drivers/acpi/arm64/iort.c
new file mode 100644
index 0000000..34b8425
--- /dev/null
+++ b/drivers/acpi/arm64/iort.c
@@ -0,0 +1,219 @@ 
+/*
+ * Copyright (C) 2016, Semihalf
+ *	Author: Tomasz Nowicki <tn@semihalf.com>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ *
+ * This file implements early detection/parsing of I/O mapping
+ * reported to OS through firmware via I/O Remapping Table (IORT)
+ * IORT document number: ARM DEN 0049A
+ */
+
+#define pr_fmt(fmt)	"ACPI: IORT: " fmt
+
+#include <linux/acpi_iort.h>
+#include <linux/kernel.h>
+#include <linux/pci.h>
+
+typedef acpi_status (*iort_find_node_callback)
+	(struct acpi_iort_node *node, void *context);
+
+/* Root pointer to the mapped IORT table */
+static struct acpi_table_header *iort_table;
+
+static LIST_HEAD(iort_msi_chip_list);
+static DEFINE_SPINLOCK(iort_msi_chip_lock);
+
+static struct acpi_iort_node *iort_scan_node(enum acpi_iort_node_type type,
+					     iort_find_node_callback callback,
+					     void *context)
+{
+	struct acpi_iort_node *iort_node, *iort_end;
+	struct acpi_table_iort *iort;
+	int i;
+
+	if (!iort_table)
+		return NULL;
+
+	/* Get the first IORT node */
+	iort = (struct acpi_table_iort *)iort_table;
+	iort_node = ACPI_ADD_PTR(struct acpi_iort_node, iort,
+				 iort->node_offset);
+	iort_end = ACPI_ADD_PTR(struct acpi_iort_node, iort_table,
+				iort_table->length);
+
+	for (i = 0; i < iort->node_count; i++) {
+		if (WARN_TAINT(iort_node >= iort_end, TAINT_FIRMWARE_WORKAROUND,
+			       "IORT node pointer overflows, bad table!\n"))
+			return NULL;
+
+		if (iort_node->type == type &&
+		    ACPI_SUCCESS(callback(iort_node, context)))
+				return iort_node;
+
+		iort_node = ACPI_ADD_PTR(struct acpi_iort_node, iort_node,
+					 iort_node->length);
+	}
+
+	return NULL;
+}
+
+static acpi_status iort_match_node_callback(struct acpi_iort_node *node,
+					    void *context)
+{
+	struct device *dev = context;
+	acpi_status status = AE_NOT_FOUND;
+
+	switch (node->type) {
+	case ACPI_IORT_NODE_NAMED_COMPONENT: {
+		struct acpi_buffer buf = { ACPI_ALLOCATE_BUFFER, NULL };
+		struct acpi_device *adev = to_acpi_device_node(dev->fwnode);
+		struct acpi_iort_named_component *ncomp;
+
+		if (!adev)
+			break;
+
+		status = acpi_get_name(adev->handle, ACPI_FULL_PATHNAME, &buf);
+		if (ACPI_FAILURE(status)) {
+			dev_warn(dev, "Can't get device full path name\n");
+			break;
+		}
+
+		ncomp = (struct acpi_iort_named_component *)node->node_data;
+		if (!strcmp(ncomp->device_name, buf.pointer))
+			status = AE_OK;
+
+		acpi_os_free(buf.pointer);
+		break;
+	}
+	case ACPI_IORT_NODE_PCI_ROOT_COMPLEX: {
+		struct acpi_iort_root_complex *pci_rc;
+		struct pci_bus *bus;
+
+		bus = to_pci_bus(dev);
+		pci_rc = (struct acpi_iort_root_complex *)node->node_data;
+
+		/*
+		 * It is assumed that PCI segment numbers maps one-to-one
+		 * with root complexes. Each segment number can represent only
+		 * one root complex.
+		 */
+		if (pci_rc->pci_segment_number == pci_domain_nr(bus))
+			status = AE_OK;
+
+		break;
+	}
+	}
+
+	return status;
+}
+
+static int iort_id_map(struct acpi_iort_id_mapping *map, u8 type, u32 rid_in,
+		       u32 *rid_out)
+{
+	/* Single mapping does not care for input id */
+	if (map->flags & ACPI_IORT_ID_SINGLE_MAPPING) {
+		if (type == ACPI_IORT_NODE_NAMED_COMPONENT ||
+		    type == ACPI_IORT_NODE_PCI_ROOT_COMPLEX) {
+			*rid_out = map->output_base;
+			return 0;
+		}
+
+		pr_warn(FW_BUG "[map %p] SINGLE MAPPING flag not allowed for node type %d, skipping ID map\n",
+			map, type);
+		return -ENXIO;
+	}
+
+	if (rid_in < map->input_base ||
+	    (rid_in >= map->input_base + map->id_count))
+		return -ENXIO;
+
+	*rid_out = map->output_base + (rid_in - map->input_base);
+	return 0;
+}
+
+static struct acpi_iort_node *iort_node_map_rid(struct acpi_iort_node *node,
+						u32 rid_in, u32 *rid_out,
+						u8 type)
+{
+	u32 rid = rid_in;
+
+	/* Parse the ID mapping tree to find specified node type */
+	while (node) {
+		struct acpi_iort_id_mapping *map;
+		int i;
+
+		if (node->type == type) {
+			if (rid_out)
+				*rid_out = rid;
+			return node;
+		}
+
+		if (!node->mapping_offset || !node->mapping_count)
+			goto fail_map;
+
+		map = ACPI_ADD_PTR(struct acpi_iort_id_mapping, node,
+				   node->mapping_offset);
+
+		/* Firmware bug! */
+		if (!map->output_reference) {
+			pr_err(FW_BUG "[node %p type %d] ID map has NULL parent reference\n",
+			       node, node->type);
+			goto fail_map;
+		}
+
+		/* Do the RID translation */
+		for (i = 0; i < node->mapping_count; i++, map++) {
+			if (!iort_id_map(map, node->type, rid, &rid))
+				break;
+		}
+
+		if (i == node->mapping_count)
+			goto fail_map;
+
+		node = ACPI_ADD_PTR(struct acpi_iort_node, iort_table,
+				    map->output_reference);
+	}
+
+fail_map:
+	/* Map input RID to output RID unchanged on mapping failure*/
+	if (rid_out)
+		*rid_out = rid_in;
+
+	return NULL;
+}
+
+static struct acpi_iort_node *iort_find_dev_node(struct device *dev)
+{
+	struct pci_bus *pbus;
+
+	if (!dev_is_pci(dev))
+		return iort_scan_node(ACPI_IORT_NODE_NAMED_COMPONENT,
+				      iort_match_node_callback, dev);
+
+	/* Find a PCI root bus */
+	pbus = to_pci_dev(dev)->bus;
+	while (!pci_is_root_bus(pbus))
+		pbus = pbus->parent;
+
+	return iort_scan_node(ACPI_IORT_NODE_PCI_ROOT_COMPLEX,
+			      iort_match_node_callback, &pbus->dev);
+}
+
+void __init acpi_iort_init(void)
+{
+	acpi_status status;
+
+	status = acpi_get_table(ACPI_SIG_IORT, 0, &iort_table);
+	if (ACPI_FAILURE(status) && status != AE_NOT_FOUND) {
+		const char *msg = acpi_format_exception(status);
+		pr_err("Failed to get table, %s\n", msg);
+	}
+}
diff --git a/drivers/acpi/bus.c b/drivers/acpi/bus.c
index 85b7d07..e56e643 100644
--- a/drivers/acpi/bus.c
+++ b/drivers/acpi/bus.c
@@ -36,6 +36,7 @@ 
 #ifdef CONFIG_X86
 #include <asm/mpspec.h>
 #endif
+#include <linux/acpi_iort.h>
 #include <linux/pci.h>
 #include <acpi/apei.h>
 #include <linux/dmi.h>
@@ -1186,6 +1187,7 @@  static int __init acpi_init(void)
 	}
 
 	pci_mmcfg_late_init();
+	acpi_iort_init();
 	acpi_scan_init();
 	acpi_ec_init();
 	acpi_debugfs_init();
diff --git a/include/linux/acpi_iort.h b/include/linux/acpi_iort.h
new file mode 100644
index 0000000..fcacaf7
--- /dev/null
+++ b/include/linux/acpi_iort.h
@@ -0,0 +1,30 @@ 
+/*
+ * Copyright (C) 2016, Semihalf
+ *	Author: Tomasz Nowicki <tn@semihalf.com>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program; if not, write to the Free Software Foundation, Inc., 59 Temple
+ * Place - Suite 330, Boston, MA 02111-1307 USA.
+ */
+
+#ifndef __ACPI_IORT_H__
+#define __ACPI_IORT_H__
+
+#include <linux/acpi.h>
+
+#ifdef CONFIG_ACPI_IORT
+void acpi_iort_init(void);
+#else
+static inline void acpi_iort_init(void) { }
+#endif
+
+#endif /* __ACPI_IORT_H__ */