[V8,2/8] ACPI: Add new IORT functions to support MSI domain handling

Commit Message

Tomasz Nowicki Aug. 11, 2016, 10:06 a.m. UTC

For ITS, MSI functionality consists on building domain stack and
during that process we need to reference to domain stack components
e.g. before we create new DOMAIN_BUS_PCI_MSI domain we need to specify
its DOMAIN_BUS_NEXUS parent domain. In order to manage that process
properly, maintain list which elements contain domain token
(unique for MSI domain stack) and ITS ID: iort_register_domain_token()
and iort_deregister_domain_token(). Then retrieve domain token
any time later with ITS ID being key off: iort_find_domain_token().
With domain token and domain type we are able to find corresponding
IRQ domain.

Since IORT is prepared to describe MSI domain on a per-device basis,
use existing IORT helpers and implement two calls:
1. iort_msi_map_rid() to map MSI RID for a device
2. iort_get_device_domain() to find domain token for a device

Signed-off-by: Tomasz Nowicki <[e-mail]>
Reviewed-by: Hanjun Guo <[e-mail]>
---
 drivers/acpi/arm64/iort.c | 169 ++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/iort.h      |  11 +++
 2 files changed, 180 insertions(+)

Comments

Lorenzo Pieralisi Aug. 12, 2016, 4:42 p.m. UTC | #1

On Thu, Aug 11, 2016 at 12:06:32PM +0200, Tomasz Nowicki wrote:

[...]

> +/**
> + * iort_register_domain_token() - register domain token and related ITS ID
> + * to the list from where we can get it back later on.
> + * @trans_id: ITS ID.
> + * @fw_node: Domain token.
> + *
> + * Returns: 0 on success, -ENOMEM if no memory when allocating list element
> + */
> +int iort_register_domain_token(int trans_id, struct fwnode_handle *fw_node)
> +{
> +	struct iort_its_msi_chip *its_msi_chip;
> +
> +	its_msi_chip = kzalloc(sizeof(*its_msi_chip), GFP_KERNEL);

I spotted this while reworking my ARM SMMU series, this may sleep
and that's no good given that we call it within the acpi_probe_lock.

Same goes for irq_domain_alloc_fwnode() (that we call in
gic_v2_acpi_init()), we have got to fix this usage, I will see with
Marc what's the best way to do it.

Lorenzo

> +	if (!its_msi_chip)
> +		return -ENOMEM;
> +
> +	its_msi_chip->fw_node = fw_node;
> +	its_msi_chip->translation_id = trans_id;
> +
> +	spin_lock(&iort_msi_chip_lock);
> +	list_add(&its_msi_chip->list, &iort_msi_chip_list);
> +	spin_unlock(&iort_msi_chip_lock);
> +
> +	return 0;
> +}
> +
> +/**
> + * iort_deregister_domain_token() - Deregister domain token based on ITS ID
> + * @trans_id: ITS ID.
> + *
> + * Returns: none.
> + */
> +void iort_deregister_domain_token(int trans_id)
> +{
> +	struct iort_its_msi_chip *its_msi_chip, *t;
> +
> +	spin_lock(&iort_msi_chip_lock);
> +	list_for_each_entry_safe(its_msi_chip, t, &iort_msi_chip_list, list) {
> +		if (its_msi_chip->translation_id == trans_id) {
> +			list_del(&its_msi_chip->list);
> +			kfree(its_msi_chip);
> +			break;
> +		}
> +	}
> +	spin_unlock(&iort_msi_chip_lock);
> +}
> +
> +/**
> + * iort_find_domain_token() - Find domain token based on given ITS ID
> + * @trans_id: ITS ID.
> + *
> + * Returns: domain token when find on the list, NULL otherwise
> + */
> +struct fwnode_handle *iort_find_domain_token(int trans_id)
> +{
> +	struct fwnode_handle *fw_node = NULL;
> +	struct iort_its_msi_chip *its_msi_chip;
> +
> +	spin_lock(&iort_msi_chip_lock);
> +	list_for_each_entry(its_msi_chip, &iort_msi_chip_list, list) {
> +		if (its_msi_chip->translation_id == trans_id) {
> +			fw_node = its_msi_chip->fw_node;
> +			break;
> +		}
> +	}
> +	spin_unlock(&iort_msi_chip_lock);
> +
> +	return fw_node;
> +}
> +
>  static struct acpi_iort_node *
>  iort_scan_node(enum acpi_iort_node_type type,
>  	       iort_find_node_callback callback, void *context)
> @@ -206,6 +285,96 @@ iort_find_dev_node(struct device *dev)
>  			      iort_match_node_callback, &pbus->dev);
>  }
>  
> +/**
> + * iort_msi_map_rid() - Map a MSI requester ID for a device
> + * @dev: The device for which the mapping is to be done.
> + * @req_id: The device requester ID.
> + *
> + * Returns: mapped MSI RID on success, input requester ID otherwise
> + */
> +u32 iort_msi_map_rid(struct device *dev, u32 req_id)
> +{
> +	struct acpi_iort_node *node;
> +	u32 dev_id;
> +
> +	if (!iort_table)
> +		return req_id;
> +
> +	node = iort_find_dev_node(dev);
> +	if (!node) {
> +		dev_err(dev, "can't find related IORT node\n");
> +		return req_id;
> +	}
> +
> +	iort_node_map_rid(node, req_id, &dev_id, ACPI_IORT_NODE_ITS_GROUP);
> +	return dev_id;
> +}
> +
> +/**
> + * iort_dev_find_its_id() - Find the ITS identifier for a device
> + * @dev: The device.
> + * @idx: Index of the ITS identifier list.
> + * @its_id: ITS identifier.
> + *
> + * Returns: 0 on success, appropriate error value otherwise
> + */
> +static int
> +iort_dev_find_its_id(struct device *dev, u32 req_id, unsigned int idx,
> +		     int *its_id)
> +{
> +	struct acpi_iort_its_group *its;
> +	struct acpi_iort_node *node;
> +
> +	node = iort_find_dev_node(dev);
> +	if (!node) {
> +		dev_err(dev, "can't find related IORT node\n");
> +		return -ENXIO;
> +	}
> +
> +	node = iort_node_map_rid(node, req_id, NULL, ACPI_IORT_NODE_ITS_GROUP);
> +	if (!node) {
> +		dev_err(dev, "can't find related ITS node\n");
> +		return -ENXIO;
> +	}
> +
> +	/* Move to ITS specific data */
> +	its = (struct acpi_iort_its_group *)node->node_data;
> +	if (idx > its->its_count) {
> +		dev_err(dev, "requested ITS ID index [%d] is greater than available [%d]\n",
> +			idx, its->its_count);
> +		return -ENXIO;
> +	}
> +
> +	*its_id = its->identifiers[idx];
> +	return 0;
> +}
> +
> +/**
> + * iort_get_device_domain() - Find MSI domain related to a device
> + * @dev: The device.
> + * @req_id: Requester ID for the device.
> + *
> + * Returns: the MSI domain for this device, NULL otherwise
> + */
> +struct irq_domain *
> +iort_get_device_domain(struct device *dev, u32 req_id)
> +{
> +	static struct fwnode_handle *handle;
> +	int its_id;
> +
> +	if (!iort_table)
> +		return NULL;
> +
> +	if (iort_dev_find_its_id(dev, req_id, 0, &its_id))
> +		return NULL;
> +
> +	handle = iort_find_domain_token(its_id);
> +	if (!handle)
> +		return NULL;
> +
> +	return irq_find_matching_fwnode(handle, DOMAIN_BUS_PCI_MSI);
> +}
> +
>  void __init iort_table_detect(void)
>  {
>  	acpi_status status;
> diff --git a/include/linux/iort.h b/include/linux/iort.h
> index cde6809..d7daba1 100644
> --- a/include/linux/iort.h
> +++ b/include/linux/iort.h
> @@ -20,11 +20,22 @@
>  #define __IORT_H__
>  
>  #include <linux/acpi.h>
> +#include <linux/fwnode.h>
> +#include <linux/irqdomain.h>
>  
> +int iort_register_domain_token(int trans_id, struct fwnode_handle *fw_node);
> +void iort_deregister_domain_token(int trans_id);
> +struct fwnode_handle *iort_find_domain_token(int trans_id);
>  #ifdef CONFIG_IORT_TABLE
>  void iort_table_detect(void);
> +u32 iort_msi_map_rid(struct device *dev, u32 req_id);
> +struct irq_domain *iort_get_device_domain(struct device *dev, u32 req_id);
>  #else
>  static inline void iort_table_detect(void) { }
> +static inline u32 iort_msi_map_rid(struct device *dev, u32 req_id)
> +{ return req_id; }
> +static inline struct irq_domain *
> +iort_get_device_domain(struct device *dev, u32 req_id) { return NULL; }
>  #endif
>  
>  #endif /* __IORT_H__ */
> -- 
> 1.9.1
>

Lv Zheng Aug. 16, 2016, 2:15 a.m. UTC | #2

Hi,

> From: [e-mail] [mailto:[e-mail]] On Behalf Of Lorenzo
> Pieralisi
> Subject: Re: [PATCH V8 2/8] ACPI: Add new IORT functions to support MSI domain handling
> 
> On Thu, Aug 11, 2016 at 12:06:32PM +0200, Tomasz Nowicki wrote:
> 
> [...]
> 
> > +/**
> > + * iort_register_domain_token() - register domain token and related ITS ID
> > + * to the list from where we can get it back later on.
> > + * @trans_id: ITS ID.
> > + * @fw_node: Domain token.
> > + *
> > + * Returns: 0 on success, -ENOMEM if no memory when allocating list element
> > + */
> > +int iort_register_domain_token(int trans_id, struct fwnode_handle *fw_node)
> > +{
> > +	struct iort_its_msi_chip *its_msi_chip;
> > +
> > +	its_msi_chip = kzalloc(sizeof(*its_msi_chip), GFP_KERNEL);
> 
> I spotted this while reworking my ARM SMMU series, this may sleep
> and that's no good given that we call it within the acpi_probe_lock.
> 
> Same goes for irq_domain_alloc_fwnode() (that we call in
> gic_v2_acpi_init()), we have got to fix this usage, I will see with
> Marc what's the best way to do it.

If we can ensure that all table device probe entries are created during link stage or early stage.
I think you can safely unlock probe lock before invoking acpi_table_parse() in __acpi_probe_device_table().

Thanks
Lv

> 
> Lorenzo
> 
> > +	if (!its_msi_chip)
> > +		return -ENOMEM;
> > +
> > +	its_msi_chip->fw_node = fw_node;
> > +	its_msi_chip->translation_id = trans_id;
> > +
> > +	spin_lock(&iort_msi_chip_lock);
> > +	list_add(&its_msi_chip->list, &iort_msi_chip_list);
> > +	spin_unlock(&iort_msi_chip_lock);
> > +
> > +	return 0;
> > +}
> > +
> > +/**
> > + * iort_deregister_domain_token() - Deregister domain token based on ITS ID
> > + * @trans_id: ITS ID.
> > + *
> > + * Returns: none.
> > + */
> > +void iort_deregister_domain_token(int trans_id)
> > +{
> > +	struct iort_its_msi_chip *its_msi_chip, *t;
> > +
> > +	spin_lock(&iort_msi_chip_lock);
> > +	list_for_each_entry_safe(its_msi_chip, t, &iort_msi_chip_list, list) {
> > +		if (its_msi_chip->translation_id == trans_id) {
> > +			list_del(&its_msi_chip->list);
> > +			kfree(its_msi_chip);
> > +			break;
> > +		}
> > +	}
> > +	spin_unlock(&iort_msi_chip_lock);
> > +}
> > +
> > +/**
> > + * iort_find_domain_token() - Find domain token based on given ITS ID
> > + * @trans_id: ITS ID.
> > + *
> > + * Returns: domain token when find on the list, NULL otherwise
> > + */
> > +struct fwnode_handle *iort_find_domain_token(int trans_id)
> > +{
> > +	struct fwnode_handle *fw_node = NULL;
> > +	struct iort_its_msi_chip *its_msi_chip;
> > +
> > +	spin_lock(&iort_msi_chip_lock);
> > +	list_for_each_entry(its_msi_chip, &iort_msi_chip_list, list) {
> > +		if (its_msi_chip->translation_id == trans_id) {
> > +			fw_node = its_msi_chip->fw_node;
> > +			break;
> > +		}
> > +	}
> > +	spin_unlock(&iort_msi_chip_lock);
> > +
> > +	return fw_node;
> > +}
> > +
> >  static struct acpi_iort_node *
> >  iort_scan_node(enum acpi_iort_node_type type,
> >  	       iort_find_node_callback callback, void *context)
> > @@ -206,6 +285,96 @@ iort_find_dev_node(struct device *dev)
> >  			      iort_match_node_callback, &pbus->dev);
> >  }
> >
> > +/**
> > + * iort_msi_map_rid() - Map a MSI requester ID for a device
> > + * @dev: The device for which the mapping is to be done.
> > + * @req_id: The device requester ID.
> > + *
> > + * Returns: mapped MSI RID on success, input requester ID otherwise
> > + */
> > +u32 iort_msi_map_rid(struct device *dev, u32 req_id)
> > +{
> > +	struct acpi_iort_node *node;
> > +	u32 dev_id;
> > +
> > +	if (!iort_table)
> > +		return req_id;
> > +
> > +	node = iort_find_dev_node(dev);
> > +	if (!node) {
> > +		dev_err(dev, "can't find related IORT node\n");
> > +		return req_id;
> > +	}
> > +
> > +	iort_node_map_rid(node, req_id, &dev_id, ACPI_IORT_NODE_ITS_GROUP);
> > +	return dev_id;
> > +}
> > +
> > +/**
> > + * iort_dev_find_its_id() - Find the ITS identifier for a device
> > + * @dev: The device.
> > + * @idx: Index of the ITS identifier list.
> > + * @its_id: ITS identifier.
> > + *
> > + * Returns: 0 on success, appropriate error value otherwise
> > + */
> > +static int
> > +iort_dev_find_its_id(struct device *dev, u32 req_id, unsigned int idx,
> > +		     int *its_id)
> > +{
> > +	struct acpi_iort_its_group *its;
> > +	struct acpi_iort_node *node;
> > +
> > +	node = iort_find_dev_node(dev);
> > +	if (!node) {
> > +		dev_err(dev, "can't find related IORT node\n");
> > +		return -ENXIO;
> > +	}
> > +
> > +	node = iort_node_map_rid(node, req_id, NULL, ACPI_IORT_NODE_ITS_GROUP);
> > +	if (!node) {
> > +		dev_err(dev, "can't find related ITS node\n");
> > +		return -ENXIO;
> > +	}
> > +
> > +	/* Move to ITS specific data */
> > +	its = (struct acpi_iort_its_group *)node->node_data;
> > +	if (idx > its->its_count) {
> > +		dev_err(dev, "requested ITS ID index [%d] is greater than available [%d]\n",
> > +			idx, its->its_count);
> > +		return -ENXIO;
> > +	}
> > +
> > +	*its_id = its->identifiers[idx];
> > +	return 0;
> > +}
> > +
> > +/**
> > + * iort_get_device_domain() - Find MSI domain related to a device
> > + * @dev: The device.
> > + * @req_id: Requester ID for the device.
> > + *
> > + * Returns: the MSI domain for this device, NULL otherwise
> > + */
> > +struct irq_domain *
> > +iort_get_device_domain(struct device *dev, u32 req_id)
> > +{
> > +	static struct fwnode_handle *handle;
> > +	int its_id;
> > +
> > +	if (!iort_table)
> > +		return NULL;
> > +
> > +	if (iort_dev_find_its_id(dev, req_id, 0, &its_id))
> > +		return NULL;
> > +
> > +	handle = iort_find_domain_token(its_id);
> > +	if (!handle)
> > +		return NULL;
> > +
> > +	return irq_find_matching_fwnode(handle, DOMAIN_BUS_PCI_MSI);
> > +}
> > +
> >  void __init iort_table_detect(void)
> >  {
> >  	acpi_status status;
> > diff --git a/include/linux/iort.h b/include/linux/iort.h
> > index cde6809..d7daba1 100644
> > --- a/include/linux/iort.h
> > +++ b/include/linux/iort.h
> > @@ -20,11 +20,22 @@
> >  #define __IORT_H__
> >
> >  #include <linux/acpi.h>
> > +#include <linux/fwnode.h>
> > +#include <linux/irqdomain.h>
> >
> > +int iort_register_domain_token(int trans_id, struct fwnode_handle *fw_node);
> > +void iort_deregister_domain_token(int trans_id);
> > +struct fwnode_handle *iort_find_domain_token(int trans_id);
> >  #ifdef CONFIG_IORT_TABLE
> >  void iort_table_detect(void);
> > +u32 iort_msi_map_rid(struct device *dev, u32 req_id);
> > +struct irq_domain *iort_get_device_domain(struct device *dev, u32 req_id);
> >  #else
> >  static inline void iort_table_detect(void) { }
> > +static inline u32 iort_msi_map_rid(struct device *dev, u32 req_id)
> > +{ return req_id; }
> > +static inline struct irq_domain *
> > +iort_get_device_domain(struct device *dev, u32 req_id) { return NULL; }
> >  #endif
> >
> >  #endif /* __IORT_H__ */
> > --
> > 1.9.1
> >
> --
> To unsubscribe from this list: send the line "unsubscribe linux-acpi" in
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> More majordomo info at  http://vger.kernel.org/majordomo-info.html

Marc Zyngier Aug. 16, 2016, 10:41 a.m. UTC | #3

On 16/08/16 03:15, Zheng, Lv wrote:
> Hi,
> 
>> From: [e-mail] [mailto:[e-mail]] On Behalf Of Lorenzo
>> Pieralisi
>> Subject: Re: [PATCH V8 2/8] ACPI: Add new IORT functions to support MSI domain handling
>>
>> On Thu, Aug 11, 2016 at 12:06:32PM +0200, Tomasz Nowicki wrote:
>>
>> [...]
>>
>>> +/**
>>> + * iort_register_domain_token() - register domain token and related ITS ID
>>> + * to the list from where we can get it back later on.
>>> + * @trans_id: ITS ID.
>>> + * @fw_node: Domain token.
>>> + *
>>> + * Returns: 0 on success, -ENOMEM if no memory when allocating list element
>>> + */
>>> +int iort_register_domain_token(int trans_id, struct fwnode_handle *fw_node)
>>> +{
>>> +	struct iort_its_msi_chip *its_msi_chip;
>>> +
>>> +	its_msi_chip = kzalloc(sizeof(*its_msi_chip), GFP_KERNEL);
>>
>> I spotted this while reworking my ARM SMMU series, this may sleep
>> and that's no good given that we call it within the acpi_probe_lock.
>>
>> Same goes for irq_domain_alloc_fwnode() (that we call in
>> gic_v2_acpi_init()), we have got to fix this usage, I will see with
>> Marc what's the best way to do it.
> 
> If we can ensure that all table device probe entries are created
> during link stage or early stage. I think you can safely unlock probe
> lock before invoking acpi_table_parse() in
> __acpi_probe_device_table().

That'd be quite risky, as this lock is the only thing that protects the
acpi_probe_entry pointer (I really wish the ACPI API was less global
variable happy), and I don't see how we can guarantee to only ever
execute this in a single-threaded environment.

An alternative would be to turn the spinlock into a mutex, which will
allow sleeping, and yet provide the required mutual exclusion.

Thanks,

	M.

Patch

diff --git a/drivers/acpi/arm64/iort.c b/drivers/acpi/arm64/iort.c
index f89056e..a03386d 100644
--- a/drivers/acpi/arm64/iort.c
+++ b/drivers/acpi/arm64/iort.c
@@ -22,12 +22,91 @@ 
 #include <linux/kernel.h>
 #include <linux/pci.h>
 
+struct iort_its_msi_chip {
+	struct list_head	list;
+	struct fwnode_handle	*fw_node;
+	u32			translation_id;
+};
+
 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);
+
+/**
+ * iort_register_domain_token() - register domain token and related ITS ID
+ * to the list from where we can get it back later on.
+ * @trans_id: ITS ID.
+ * @fw_node: Domain token.
+ *
+ * Returns: 0 on success, -ENOMEM if no memory when allocating list element
+ */
+int iort_register_domain_token(int trans_id, struct fwnode_handle *fw_node)
+{
+	struct iort_its_msi_chip *its_msi_chip;
+
+	its_msi_chip = kzalloc(sizeof(*its_msi_chip), GFP_KERNEL);
+	if (!its_msi_chip)
+		return -ENOMEM;
+
+	its_msi_chip->fw_node = fw_node;
+	its_msi_chip->translation_id = trans_id;
+
+	spin_lock(&iort_msi_chip_lock);
+	list_add(&its_msi_chip->list, &iort_msi_chip_list);
+	spin_unlock(&iort_msi_chip_lock);
+
+	return 0;
+}
+
+/**
+ * iort_deregister_domain_token() - Deregister domain token based on ITS ID
+ * @trans_id: ITS ID.
+ *
+ * Returns: none.
+ */
+void iort_deregister_domain_token(int trans_id)
+{
+	struct iort_its_msi_chip *its_msi_chip, *t;
+
+	spin_lock(&iort_msi_chip_lock);
+	list_for_each_entry_safe(its_msi_chip, t, &iort_msi_chip_list, list) {
+		if (its_msi_chip->translation_id == trans_id) {
+			list_del(&its_msi_chip->list);
+			kfree(its_msi_chip);
+			break;
+		}
+	}
+	spin_unlock(&iort_msi_chip_lock);
+}
+
+/**
+ * iort_find_domain_token() - Find domain token based on given ITS ID
+ * @trans_id: ITS ID.
+ *
+ * Returns: domain token when find on the list, NULL otherwise
+ */
+struct fwnode_handle *iort_find_domain_token(int trans_id)
+{
+	struct fwnode_handle *fw_node = NULL;
+	struct iort_its_msi_chip *its_msi_chip;
+
+	spin_lock(&iort_msi_chip_lock);
+	list_for_each_entry(its_msi_chip, &iort_msi_chip_list, list) {
+		if (its_msi_chip->translation_id == trans_id) {
+			fw_node = its_msi_chip->fw_node;
+			break;
+		}
+	}
+	spin_unlock(&iort_msi_chip_lock);
+
+	return fw_node;
+}
+
 static struct acpi_iort_node *
 iort_scan_node(enum acpi_iort_node_type type,
 	       iort_find_node_callback callback, void *context)
@@ -206,6 +285,96 @@  iort_find_dev_node(struct device *dev)
 			      iort_match_node_callback, &pbus->dev);
 }
 
+/**
+ * iort_msi_map_rid() - Map a MSI requester ID for a device
+ * @dev: The device for which the mapping is to be done.
+ * @req_id: The device requester ID.
+ *
+ * Returns: mapped MSI RID on success, input requester ID otherwise
+ */
+u32 iort_msi_map_rid(struct device *dev, u32 req_id)
+{
+	struct acpi_iort_node *node;
+	u32 dev_id;
+
+	if (!iort_table)
+		return req_id;
+
+	node = iort_find_dev_node(dev);
+	if (!node) {
+		dev_err(dev, "can't find related IORT node\n");
+		return req_id;
+	}
+
+	iort_node_map_rid(node, req_id, &dev_id, ACPI_IORT_NODE_ITS_GROUP);
+	return dev_id;
+}
+
+/**
+ * iort_dev_find_its_id() - Find the ITS identifier for a device
+ * @dev: The device.
+ * @idx: Index of the ITS identifier list.
+ * @its_id: ITS identifier.
+ *
+ * Returns: 0 on success, appropriate error value otherwise
+ */
+static int
+iort_dev_find_its_id(struct device *dev, u32 req_id, unsigned int idx,
+		     int *its_id)
+{
+	struct acpi_iort_its_group *its;
+	struct acpi_iort_node *node;
+
+	node = iort_find_dev_node(dev);
+	if (!node) {
+		dev_err(dev, "can't find related IORT node\n");
+		return -ENXIO;
+	}
+
+	node = iort_node_map_rid(node, req_id, NULL, ACPI_IORT_NODE_ITS_GROUP);
+	if (!node) {
+		dev_err(dev, "can't find related ITS node\n");
+		return -ENXIO;
+	}
+
+	/* Move to ITS specific data */
+	its = (struct acpi_iort_its_group *)node->node_data;
+	if (idx > its->its_count) {
+		dev_err(dev, "requested ITS ID index [%d] is greater than available [%d]\n",
+			idx, its->its_count);
+		return -ENXIO;
+	}
+
+	*its_id = its->identifiers[idx];
+	return 0;
+}
+
+/**
+ * iort_get_device_domain() - Find MSI domain related to a device
+ * @dev: The device.
+ * @req_id: Requester ID for the device.
+ *
+ * Returns: the MSI domain for this device, NULL otherwise
+ */
+struct irq_domain *
+iort_get_device_domain(struct device *dev, u32 req_id)
+{
+	static struct fwnode_handle *handle;
+	int its_id;
+
+	if (!iort_table)
+		return NULL;
+
+	if (iort_dev_find_its_id(dev, req_id, 0, &its_id))
+		return NULL;
+
+	handle = iort_find_domain_token(its_id);
+	if (!handle)
+		return NULL;
+
+	return irq_find_matching_fwnode(handle, DOMAIN_BUS_PCI_MSI);
+}
+
 void __init iort_table_detect(void)
 {
 	acpi_status status;
diff --git a/include/linux/iort.h b/include/linux/iort.h
index cde6809..d7daba1 100644
--- a/include/linux/iort.h
+++ b/include/linux/iort.h
@@ -20,11 +20,22 @@ 
 #define __IORT_H__
 
 #include <linux/acpi.h>
+#include <linux/fwnode.h>
+#include <linux/irqdomain.h>
 
+int iort_register_domain_token(int trans_id, struct fwnode_handle *fw_node);
+void iort_deregister_domain_token(int trans_id);
+struct fwnode_handle *iort_find_domain_token(int trans_id);
 #ifdef CONFIG_IORT_TABLE
 void iort_table_detect(void);
+u32 iort_msi_map_rid(struct device *dev, u32 req_id);
+struct irq_domain *iort_get_device_domain(struct device *dev, u32 req_id);
 #else
 static inline void iort_table_detect(void) { }
+static inline u32 iort_msi_map_rid(struct device *dev, u32 req_id)
+{ return req_id; }
+static inline struct irq_domain *
+iort_get_device_domain(struct device *dev, u32 req_id) { return NULL; }
 #endif
 
 #endif /* __IORT_H__ */