GENERIC SYSTEM INTERCONNECT SUBSYSTEM¶
Introduction¶
This framework is designed to provide a standard kernel interface to control the settings of the interconnects on an SoC. These settings can be throughput, latency and priority between multiple interconnected devices or functional blocks. This can be controlled dynamically in order to save power or provide maximum performance.
The interconnect bus is hardware with configurable parameters, which can be set on a data path according to the requests received from various drivers. An example of interconnect buses are the interconnects between various components or functional blocks in chipsets. There can be multiple interconnects on an SoC that can be multi-tiered.
Below is a simplified diagram of a real-world SoC interconnect bus topology.
+----------------+ +----------------+
| HW Accelerator |--->| M NoC |<---------------+
+----------------+ +----------------+ |
| | +------------+
+-----+ +-------------+ V +------+ | |
| DDR | | +--------+ | PCIe | | |
+-----+ | | Slaves | +------+ | |
^ ^ | +--------+ | | C NoC |
| | V V | |
+------------------+ +------------------------+ | | +-----+
| |-->| |-->| |-->| CPU |
| |-->| |<--| | +-----+
| Mem NoC | | S NoC | +------------+
| |<--| |---------+ |
| |<--| |<------+ | | +--------+
+------------------+ +------------------------+ | | +-->| Slaves |
^ ^ ^ ^ ^ | | +--------+
| | | | | | V
+------+ | +-----+ +-----+ +---------+ +----------------+ +--------+
| CPUs | | | GPU | | DSP | | Masters |-->| P NoC |-->| Slaves |
+------+ | +-----+ +-----+ +---------+ +----------------+ +--------+
|
+-------+
| Modem |
+-------+
Terminology¶
Interconnect provider is the software definition of the interconnect hardware. The interconnect providers on the above diagram are M NoC, S NoC, C NoC, P NoC and Mem NoC.
Interconnect node is the software definition of the interconnect hardware port. Each interconnect provider consists of multiple interconnect nodes, which are connected to other SoC components including other interconnect providers. The point on the diagram where the CPUs connect to the memory is called an interconnect node, which belongs to the Mem NoC interconnect provider.
Interconnect endpoints are the first or the last element of the path. Every endpoint is a node, but not every node is an endpoint.
Interconnect path is everything between two endpoints including all the nodes that have to be traversed to reach from a source to destination node. It may include multiple master-slave pairs across several interconnect providers.
Interconnect consumers are the entities which make use of the data paths exposed by the providers. The consumers send requests to providers requesting various throughput, latency and priority. Usually the consumers are device drivers, that send request based on their needs. An example for a consumer is a video decoder that supports various formats and image sizes.
Interconnect providers¶
Interconnect provider is an entity that implements methods to initialize and configure interconnect bus hardware. The interconnect provider drivers should be registered with the interconnect provider core.
-
struct
icc_onecell_data¶ driver data for onecell interconnect providers
Definition
struct icc_onecell_data {
unsigned int num_nodes;
struct icc_node *nodes[];
};
Members
num_nodesnumber of nodes in this device
nodesarray of pointers to the nodes in this device
-
struct
icc_provider¶ interconnect provider (controller) entity that might provide multiple interconnect controls
Definition
struct icc_provider {
struct list_head provider_list;
struct list_head nodes;
int (*set)(struct icc_node *src, struct icc_node *dst);
int (*aggregate)(struct icc_node *node, u32 tag, u32 avg_bw, u32 peak_bw, u32 *agg_avg, u32 *agg_peak);
void (*pre_aggregate)(struct icc_node *node);
struct icc_node* (*xlate)(struct of_phandle_args *spec, void *data);
struct device *dev;
int users;
void *data;
};
Members
provider_listlist of the registered interconnect providers
nodesinternal list of the interconnect provider nodes
setpointer to device specific set operation function
aggregatepointer to device specific aggregate operation function
pre_aggregatepointer to device specific function that is called before the aggregation begins (optional)
xlateprovider-specific callback for mapping nodes from phandle arguments
devthe device this interconnect provider belongs to
userscount of active users
datapointer to private data
-
struct
icc_node¶ entity that is part of the interconnect topology
Definition
struct icc_node {
int id;
const char *name;
struct icc_node **links;
size_t num_links;
struct icc_provider *provider;
struct list_head node_list;
struct list_head search_list;
struct icc_node *reverse;
u8 is_traversed:1;
struct hlist_head req_list;
u32 avg_bw;
u32 peak_bw;
void *data;
};
Members
idplatform specific node id
namenode name used in debugfs
linksa list of targets pointing to where we can go next when traversing
num_linksnumber of links to other interconnect nodes
providerpoints to the interconnect provider of this node
node_listthe list entry in the parent provider's "nodes" list
search_listlist used when walking the nodes graph
reversepointer to previous node when walking the nodes graph
is_traversedflag that is used when walking the nodes graph
req_lista list of QoS constraint requests associated with this node
avg_bwaggregated value of average bandwidth requests from all consumers
peak_bwaggregated value of peak bandwidth requests from all consumers
datapointer to private data
Interconnect consumers¶
Interconnect consumers are the clients which use the interconnect APIs to get paths between endpoints and set their bandwidth/latency/QoS requirements for these interconnect paths. These interfaces are not currently documented.