[v6,0/8] Introduce on-chip interconnect API

Message ID 20180709155104.25528-1-georgi.djakov@linaro.org
Headers show
Series
  • Introduce on-chip interconnect API
Related show

Message

Georgi Djakov July 9, 2018, 3:50 p.m.
Modern SoCs have multiple processors and various dedicated cores (video, gpu,
graphics, modem). These cores are talking to each other and can generate a
lot of data flowing through the on-chip interconnects. These interconnect
buses could form different topologies such as crossbar, point to point buses,
hierarchical buses or use the network-on-chip concept.

These buses have been sized usually to handle use cases with high data
throughput but it is not necessary all the time and consume a lot of power.
Furthermore, the priority between masters can vary depending on the running
use case like video playback or CPU intensive tasks.

Having an API to control the requirement of the system in terms of bandwidth
and QoS, so we can adapt the interconnect configuration to match those by
scaling the frequencies, setting link priority and tuning QoS parameters.
This configuration can be a static, one-time operation done at boot for some
platforms or a dynamic set of operations that happen at run-time.

This patchset introduce a new API to get the requirement and configure the
interconnect buses across the entire chipset to fit with the current demand.
The API is NOT for changing the performance of the endpoint devices, but only
the interconnect path in between them.

The API is using a consumer/provider-based model, where the providers are
the interconnect buses and the consumers could be various drivers.
The consumers request interconnect resources (path) to an endpoint and set
the desired constraints on this data flow path. The provider(s) receive
requests from consumers and aggregate these requests for all master-slave
pairs on that path. Then the providers configure each participating in the
topology node according to the requested data flow path, physical links and
constraints. The topology could be complicated and multi-tiered and is SoC
specific.

Below is a simplified diagram of a real-world SoC topology. The interconnect
providers are the NoCs.

+----------------+    +----------------+
| 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 |
      +-------+

TODO:
 * Create icc_set_extended() to handle parameters such as latency and other
   QoS values.
 * Convert from using global node identifiers to local per provider ids.
 * Cache the path between the nodes instead of walking the graph on each get().
 * Sync interconnect requests with the idle state of the device.

Changes since patchset v5 (https://lkml.org/lkml/2018/6/20/453)
* Fix the modular build, make rpm-smd driver a module.
* Optimize locking and move to higher level. (Evan)
* Code cleanups. Fix typos. (Evan, Matthias)
* Add the source node to the path. (Evan)
* Rename path_allocate() to path_init() with minor refactoring. (Evan)
* Rename *_remove() functions to *_destroy().
* Return fixed errors in icc_link_destroy(). (Evan)
* Fix krealloc() usage in icc_link_destroy(). (Evan)
* Add missing kfree() in icc_node_create(). (Matthias)
* Make icc_node_add() return void. (Matthias)
* Change mutex_init to mutex_lock in icc_provider_add(). (Matthias)
* Add new icc_node_del() function to delete nodes from provider.
* Fix the header guard to reflect the path in smd-rpm.h. (Evan)
* Check for errors returned by qcom_icc_rpm_smd_send(). (Evan)
* Propagate the error of icc_provider_del(). (Evan)

Changes since patchset v4 (https://lkml.org/lkml/2018/3/9/856)
* Simplified locking by using a single global mutex. (Evan)
* Changed the aggregation function interface.
* Implemented functions for node, link, provider removal. (Evan)
* Naming changes on variables and functions, removed redundant code. (Evan)
* Fixes and clarifications in the docs. (Matthias, Evan, Amit, Alexandre)
* Removed mandatory reg DT property, made interconnect-names optional. (Bjorn)
* Made interconnect-cells property required to align with other bindings. (Neil)
* Moved msm8916 specific bindings into a separate file and patch. (Bjorn)
* Use the names, instead of the hardcoded ids for topology. (Matthias)
* Init the node before creating the links. (Evan)
* Added icc_units_to_bps macro. (Amit)

Changes since patchset v3 (https://lkml.org/lkml/2017/9/8/544)
* Refactored the constraints aggregation.
* Use the IDR API.
* Split the provider and consumer bindings into separate patches and propose
  new bindings for consumers, which allows to specify the local source port.
* Adopted the icc_ prefix for API functions.
* Introduced separate API functions for creating interconnect nodes and links.
* Added DT lookup support in addition to platform data.
* Dropped the event tracing patch for now.
* Added a patch to provide summary via debugfs.
* Use macro for the list of topology definitions in the platform driver.
* Various minor changes.

Changes since patchset v2 (https://lkml.org/lkml/2017/7/20/825)
* Split the aggregation into per node and per provider. Cache the
  aggregated values.
* Various small refactorings and cleanups in the framework.
* Added a patch introducing basic tracepoint support for monitoring
  the time required to update the interconnect nodes.

Changes since patchset v1 (https://lkml.org/lkml/2017/6/27/890)
* Updates in the documentation.
* Changes in request aggregation, locking.
* Dropped the aggregate() callback and use the default as it currently
  sufficient for the single vendor driver. Will add it later when needed.
* Dropped the dt-bindings draft patch for now.

Changes since RFC v2 (https://lkml.org/lkml/2017/6/12/316)
* Converted documentation to rst format.
* Fixed an incorrect call to mutex_lock. Renamed max_bw to peak_bw.

Changes since RFC v1 (https://lkml.org/lkml/2017/5/15/605)
* Refactored code into shorter functions.
* Added a new aggregate() API function.
* Rearranged some structs to reduce padding bytes.

Changes since RFC v0 (https://lkml.org/lkml/2017/3/1/599)
* Removed DT support and added optional Patch 3 with new bindings proposal.
* Converted the topology into internal driver data.
* Made the framework modular.
* interconnect_get() now takes (src and dst ports as arguments).
* Removed public declarations of some structs.
* Now passing prev/next nodes to the vendor driver.
* Properly remove requests on _put().
* Added refcounting.
* Updated documentation.
* Changed struct interconnect_path to use array instead of linked list.

Georgi Djakov (8):
  interconnect: Add generic on-chip interconnect API
  dt-bindings: Introduce interconnect provider bindings
  interconnect: Add debugfs support
  interconnect: qcom: Add RPM communication
  dt-bindings: interconnect: Document qcom,msm8916 NoC bindings
  interconnect: qcom: Add msm8916 interconnect provider driver
  dt-bindings: Introduce interconnect consumers bindings
  interconnect: Allow endpoints translation via DT

 .../bindings/interconnect/interconnect.txt    |  60 ++
 .../bindings/interconnect/qcom-msm8916.txt    |  39 +
 .../bindings/interconnect/qcom-smd.txt        |  32 +
 Documentation/interconnect/interconnect.rst   |  96 +++
 drivers/Kconfig                               |   2 +
 drivers/Makefile                              |   1 +
 drivers/interconnect/Kconfig                  |  15 +
 drivers/interconnect/Makefile                 |   3 +
 drivers/interconnect/core.c                   | 737 ++++++++++++++++++
 drivers/interconnect/qcom/Kconfig             |  21 +
 drivers/interconnect/qcom/Makefile            |   4 +
 drivers/interconnect/qcom/msm8916.c           | 499 ++++++++++++
 drivers/interconnect/qcom/smd-rpm.c           |  91 +++
 drivers/interconnect/qcom/smd-rpm.h           |  15 +
 include/dt-bindings/interconnect/qcom.h       | 350 +++++++++
 include/linux/interconnect-provider.h         | 130 +++
 include/linux/interconnect.h                  |  49 ++
 17 files changed, 2144 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/interconnect/interconnect.txt
 create mode 100644 Documentation/devicetree/bindings/interconnect/qcom-msm8916.txt
 create mode 100644 Documentation/devicetree/bindings/interconnect/qcom-smd.txt
 create mode 100644 Documentation/interconnect/interconnect.rst
 create mode 100644 drivers/interconnect/Kconfig
 create mode 100644 drivers/interconnect/Makefile
 create mode 100644 drivers/interconnect/core.c
 create mode 100644 drivers/interconnect/qcom/Kconfig
 create mode 100644 drivers/interconnect/qcom/Makefile
 create mode 100644 drivers/interconnect/qcom/msm8916.c
 create mode 100644 drivers/interconnect/qcom/smd-rpm.c
 create mode 100644 drivers/interconnect/qcom/smd-rpm.h
 create mode 100644 include/dt-bindings/interconnect/qcom.h
 create mode 100644 include/linux/interconnect-provider.h
 create mode 100644 include/linux/interconnect.h

Comments

Evan Green July 10, 2018, 10:34 p.m. | #1
Ahoy Georgi!
On Mon, Jul 9, 2018 at 8:51 AM Georgi Djakov <georgi.djakov@linaro.org> wrote:
>

> This patch introduces a new API to get requirements and configure the

> interconnect buses across the entire chipset to fit with the current

> demand.

>

> The API is using a consumer/provider-based model, where the providers are

> the interconnect buses and the consumers could be various drivers.

> The consumers request interconnect resources (path) between endpoints and

> set the desired constraints on this data flow path. The providers receive

> requests from consumers and aggregate these requests for all master-slave

> pairs on that path. Then the providers configure each participating in the

> topology node according to the requested data flow path, physical links and

> constraints. The topology could be complicated and multi-tiered and is SoC

> specific.

>

> Signed-off-by: Georgi Djakov <georgi.djakov@linaro.org>

> ---

>  Documentation/interconnect/interconnect.rst |  96 ++++

>  drivers/Kconfig                             |   2 +

>  drivers/Makefile                            |   1 +

>  drivers/interconnect/Kconfig                |  10 +

>  drivers/interconnect/Makefile               |   2 +

>  drivers/interconnect/core.c                 | 597 ++++++++++++++++++++

>  include/linux/interconnect-provider.h       | 130 +++++

>  include/linux/interconnect.h                |  42 ++

>  8 files changed, 880 insertions(+)

>  create mode 100644 Documentation/interconnect/interconnect.rst

>  create mode 100644 drivers/interconnect/Kconfig

>  create mode 100644 drivers/interconnect/Makefile

>  create mode 100644 drivers/interconnect/core.c

>  create mode 100644 include/linux/interconnect-provider.h

>  create mode 100644 include/linux/interconnect.h

>

> diff --git a/Documentation/interconnect/interconnect.rst b/Documentation/interconnect/interconnect.rst

> new file mode 100644

> index 000000000000..a1ebd83ad0a1

> --- /dev/null

> +++ b/Documentation/interconnect/interconnect.rst

> @@ -0,0 +1,96 @@

> +.. SPDX-License-Identifier: GPL-2.0

> +

> +=====================================

> +GENERIC SYSTEM INTERCONNECT SUBSYSTEM

> +=====================================

> +

> +Introduction

> +------------

> +

> +This framework is designed to provide a standard kernel interface to control

> +the settings of the interconnects on a 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 a 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 a 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 connects to the memory is


CPUs connect

> +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 a interconnect bus hardware. The interconnect provider drivers should

> +be registered with the interconnect provider core.

> +

> +The interconnect framework provider API functions are documented in

> +.. kernel-doc:: include/linux/interconnect-provider.h

> +

> +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.

> +

> +The interconnect framework consumer API functions are documented in

> +.. kernel-doc:: include/linux/interconnect.h

> diff --git a/drivers/Kconfig b/drivers/Kconfig

> index 95b9ccc08165..3ed6ede9d021 100644

> --- a/drivers/Kconfig

> +++ b/drivers/Kconfig

> @@ -217,4 +217,6 @@ source "drivers/siox/Kconfig"

>

>  source "drivers/slimbus/Kconfig"

>

> +source "drivers/interconnect/Kconfig"

> +

>  endmenu

> diff --git a/drivers/Makefile b/drivers/Makefile

> index 24cd47014657..0cca95740d9b 100644

> --- a/drivers/Makefile

> +++ b/drivers/Makefile

> @@ -185,3 +185,4 @@ obj-$(CONFIG_TEE)           += tee/

>  obj-$(CONFIG_MULTIPLEXER)      += mux/

>  obj-$(CONFIG_UNISYS_VISORBUS)  += visorbus/

>  obj-$(CONFIG_SIOX)             += siox/

> +obj-$(CONFIG_INTERCONNECT)     += interconnect/

> diff --git a/drivers/interconnect/Kconfig b/drivers/interconnect/Kconfig

> new file mode 100644

> index 000000000000..a261c7d41deb

> --- /dev/null

> +++ b/drivers/interconnect/Kconfig

> @@ -0,0 +1,10 @@

> +menuconfig INTERCONNECT

> +       tristate "On-Chip Interconnect management support"

> +       help

> +         Support for management of the on-chip interconnects.

> +

> +         This framework is designed to provide a generic interface for

> +         managing the interconnects in a SoC.

> +

> +         If unsure, say no.

> +

> diff --git a/drivers/interconnect/Makefile b/drivers/interconnect/Makefile

> new file mode 100644

> index 000000000000..97fca2e09d24

> --- /dev/null

> +++ b/drivers/interconnect/Makefile

> @@ -0,0 +1,2 @@

> +# SPDX-License-Identifier: GPL-2.0

> +obj-$(CONFIG_INTERCONNECT)             += core.o

> diff --git a/drivers/interconnect/core.c b/drivers/interconnect/core.c

> new file mode 100644

> index 000000000000..63707c3c3d48

> --- /dev/null

> +++ b/drivers/interconnect/core.c

> @@ -0,0 +1,597 @@

> +// SPDX-License-Identifier: GPL-2.0

> +/*

> + * Interconnect framework core driver

> + *

> + * Copyright (c) 2018, Linaro Ltd.

> + * Author: Georgi Djakov <georgi.djakov@linaro.org>

> + */

> +

> +#include <linux/device.h>

> +#include <linux/idr.h>

> +#include <linux/init.h>

> +#include <linux/interconnect.h>

> +#include <linux/interconnect-provider.h>

> +#include <linux/list.h>

> +#include <linux/module.h>

> +#include <linux/mutex.h>


I needed to add #include <linux/overflow.h> to get struct_size() (used
in path_init) in order to get this to compile, but maybe my kernel is
missing some upstream picks.

> +#include <linux/slab.h>

> +

> +static DEFINE_IDR(icc_idr);

> +static LIST_HEAD(icc_provider_list);

> +static DEFINE_MUTEX(icc_lock);

> +

> +/**

> + * struct icc_req - constraints that are attached to each node

> + *

> + * @req_node: entry in list of requests for the particular @node

> + * @node: the interconnect node to which this constraint applies

> + * @dev: reference to the device that sets the constraints

> + * @avg_bw: an integer describing the average bandwidth in kbps

> + * @peak_bw: an integer describing the peak bandwidth in kbps

> + */

> +struct icc_req {

> +       struct hlist_node req_node;

> +       struct icc_node *node;

> +       struct device *dev;

> +       u32 avg_bw;

> +       u32 peak_bw;

> +};

> +

> +/**

> + * struct icc_path - interconnect path structure

> + * @num_nodes: number of hops (nodes)

> + * @reqs: array of the requests applicable to this path of nodes

> + */

> +struct icc_path {

> +       size_t num_nodes;

> +       struct icc_req reqs[];

> +};

> +

> +static struct icc_node *node_find(const int id)

> +{

> +       return idr_find(&icc_idr, id);


Wasn't there going to be a warning if the mutex is not held?

> +}

> +

> +static struct icc_path *path_init(struct device *dev, struct icc_node *dst,

> +                                 ssize_t num_nodes)

> +{

> +       struct icc_node *node = dst;

> +       struct icc_path *path;

> +       size_t i;

> +

> +       path = kzalloc(struct_size(path, reqs, num_nodes), GFP_KERNEL);

> +       if (!path)

> +               return ERR_PTR(-ENOMEM);

> +

> +       path->num_nodes = num_nodes;

> +


There should probably also be a warning here about holding the lock,
since you're modifying node->req_list.

> +       for (i = 0; i < num_nodes; i++) {

> +               hlist_add_head(&path->reqs[i].req_node, &node->req_list);

> +

> +               path->reqs[i].node = node;

> +               path->reqs[i].dev = dev;

> +               /* reference to previous node was saved during path traversal */

> +               node = node->reverse;

> +       }

> +

> +       return path;

> +}

> +

> +static struct icc_path *path_find(struct device *dev, struct icc_node *src,

> +                                 struct icc_node *dst)

> +{

> +       struct icc_node *n, *node = NULL;

> +       struct icc_provider *provider;

> +       struct list_head traverse_list;

> +       struct list_head edge_list;

> +       struct list_head visited_list;

> +       size_t i, depth = 1;

> +       bool found = false;

> +       int ret = -EPROBE_DEFER;

> +

> +       INIT_LIST_HEAD(&traverse_list);

> +       INIT_LIST_HEAD(&edge_list);

> +       INIT_LIST_HEAD(&visited_list);

> +


A warning here too about holding the lock would also be good, since
multiple people in here at once would be bad.

> +       list_add_tail(&src->search_list, &traverse_list);

> +       src->reverse = NULL;

> +

> +       do {

> +               list_for_each_entry_safe(node, n, &traverse_list, search_list) {

> +                       if (node == dst) {

> +                               found = true;

> +                               list_add(&node->search_list, &visited_list);

> +                               break;

> +                       }

> +                       for (i = 0; i < node->num_links; i++) {

> +                               struct icc_node *tmp = node->links[i];

> +

> +                               if (!tmp) {

> +                                       ret = -ENOENT;

> +                                       goto out;

> +                               }

> +

> +                               if (tmp->is_traversed)

> +                                       continue;

> +

> +                               tmp->is_traversed = true;

> +                               tmp->reverse = node;

> +                               list_add(&tmp->search_list, &edge_list);

> +                       }

> +               }

> +               if (found)

> +                       break;

> +

> +               list_splice_init(&traverse_list, &visited_list);

> +               list_splice_init(&edge_list, &traverse_list);

> +

> +               /* count the hops including the source */

> +               depth++;

> +

> +       } while (!list_empty(&traverse_list));

> +

> +out:

> +       /* reset the traversed state */

> +       list_for_each_entry(provider, &icc_provider_list, provider_list)

> +               list_for_each_entry(n, &provider->nodes, node_list)

> +                       n->is_traversed = false;


I think I missed this on the last round. I thought you had been
keeping visited_list specifically so you could use it to reset
is_traversed here. But now it looks like you're going through the
entire graph. What happened?

> +

> +       if (found) {

> +               struct icc_path *path = path_init(dev, dst, depth);

> +

> +               if (IS_ERR(path))

> +                       return path;

> +

> +               for (i = 0; i < path->num_nodes; i++) {

> +                       node = path->reqs[i].node;

> +                       node->provider->users++;


Hm, should this go in path_init as well? What do you think? You sort
of become a user once you tack your path.req_node on the
node.req_list.

> +               }

> +               return path;

> +       }

> +

> +       return ERR_PTR(ret);

> +}

> +

> +/*

> + * We want the path to honor all bandwidth requests, so the average

> + * bandwidth requirements from each consumer are aggregated at each node

> + * and provider level. By default the average bandwidth is the sum of all

> + * averages and the peak will be the highest of all peak bandwidth requests.

> + */

> +

> +static int aggregate_requests(struct icc_node *node)

> +{

> +       struct icc_provider *p = node->provider;

> +       struct icc_req *r;

> +

> +       node->avg_bw = 0;

> +       node->peak_bw = 0;

> +

> +       hlist_for_each_entry(r, &node->req_list, req_node)

> +               p->aggregate(node, r->avg_bw, r->peak_bw,

> +                            &node->avg_bw, &node->peak_bw);

> +

> +       return 0;

> +}


This doesn't have to be addressed in this series, but I wonder if the
aggregate() callback should be made aware of whether its aggregating
requests within a node, or nodes within a provider? Right now the
aggregate callback has no way of knowing what it's aggregating for; I
guess the question is: might it need to? I'm unsure.

> +

> +static void aggregate_provider(struct icc_provider *p)

> +{

> +       struct icc_node *n;

> +

> +       p->avg_bw = 0;

> +       p->peak_bw = 0;

> +

> +       list_for_each_entry(n, &p->nodes, node_list)

> +               p->aggregate(n, n->avg_bw, n->peak_bw,

> +                            &p->avg_bw, &p->peak_bw);

> +}

> +

> +static int apply_constraints(struct icc_path *path)

> +{

> +       struct icc_node *next, *prev = NULL;

> +       int ret;

> +       int i;

> +

> +       for (i = 0; i < path->num_nodes; i++, prev = next) {

> +               struct icc_provider *p;

> +

> +               next = path->reqs[i].node;

> +               /*

> +                * Both endpoints should be valid master-slave pairs of the

> +                * same interconnect provider that will be configured.

> +                */

> +               if (!prev || next->provider != prev->provider)

> +                       continue;

> +

> +               p = next->provider;

> +

> +               aggregate_provider(p);

> +

> +               /* set the constraints */

> +               ret = p->set(prev, next, p->avg_bw, p->peak_bw);

> +               if (ret)

> +                       goto out;

> +       }

> +out:

> +       return ret;

> +}

> +

> +/**

> + * icc_set() - set constraints on an interconnect path between two endpoints

> + * @path: reference to the path returned by icc_get()

> + * @avg_bw: average bandwidth in kbps

> + * @peak_bw: peak bandwidth in kbps

> + *

> + * This function is used by an interconnect consumer to express its own needs

> + * in terms of bandwidth for a previously requested path between two endpoints.

> + * The requests are aggregated and each node is updated accordingly. The entire

> + * path is locked by a mutex to ensure that the set() is completed.

> + * The @path can be NULL when the "interconnects" DT properties is missing,

> + * which will mean that no constraints will be set.

> + *

> + * Returns 0 on success, or an appropriate error code otherwise.

> + */

> +int icc_set(struct icc_path *path, u32 avg_bw, u32 peak_bw)

> +{

> +       struct icc_node *node;

> +       struct icc_provider *p;

> +       size_t i;

> +       int ret;

> +

> +       if (!path)

> +               return 0;

> +

> +       mutex_lock(&icc_lock);

> +

> +       for (i = 0; i < path->num_nodes; i++) {

> +               node = path->reqs[i].node;

> +               p = node->provider;

> +

> +               /* update the consumer request for this path */

> +               path->reqs[i].avg_bw = avg_bw;

> +               path->reqs[i].peak_bw = peak_bw;

> +

> +               /* aggregate requests for this node */

> +               aggregate_requests(node);

> +       }

> +

> +       ret = apply_constraints(path);

> +       if (ret)

> +               pr_err("interconnect: error applying constraints (%d)", ret);

> +

> +       mutex_unlock(&icc_lock);

> +

> +       return ret;

> +}

> +EXPORT_SYMBOL_GPL(icc_set);

> +

> +/**

> + * icc_get() - return a handle for path between two endpoints

> + * @dev: the device requesting the path

> + * @src_id: source device port id

> + * @dst_id: destination device port id

> + *

> + * This function will search for a path between two endpoints and return an

> + * icc_path handle on success. Use icc_put() to release

> + * constraints when the they are not needed anymore.

> + *

> + * Return: icc_path pointer on success, or ERR_PTR() on error

> + */

> +struct icc_path *icc_get(struct device *dev, const int src_id, const int dst_id)

> +{

> +       struct icc_node *src, *dst;

> +       struct icc_path *path = ERR_PTR(-EPROBE_DEFER);

> +

> +       mutex_lock(&icc_lock);

> +

> +       src = node_find(src_id);

> +       if (!src)

> +               goto out;

> +

> +       dst = node_find(dst_id);

> +       if (!dst)

> +               goto out;

> +

> +       path = path_find(dev, src, dst);

> +       if (IS_ERR(path))

> +               dev_err(dev, "%s: invalid path=%ld\n", __func__, PTR_ERR(path));

> +

> +out:

> +       mutex_unlock(&icc_lock);

> +       return path;

> +}

> +EXPORT_SYMBOL_GPL(icc_get);

> +

> +/**

> + * icc_put() - release the reference to the icc_path

> + * @path: interconnect path

> + *

> + * Use this function to release the constraints on a path when the path is

> + * no longer needed. The constraints will be re-aggregated.

> + */

> +void icc_put(struct icc_path *path)

> +{

> +       struct icc_node *node;

> +       size_t i;

> +       int ret;

> +

> +       if (!path || WARN_ON(IS_ERR(path)))

> +               return;

> +

> +       ret = icc_set(path, 0, 0);

> +       if (ret)

> +               pr_err("%s: error (%d)\n", __func__, ret);

> +

> +       mutex_lock(&icc_lock);

> +       for (i = 0; i < path->num_nodes; i++) {

> +               node = path->reqs[i].node;

> +               hlist_del(&path->reqs[i].req_node);

> +


Maybe a warning if users is zero?

> +               node->provider->users--;

> +       }

> +       mutex_unlock(&icc_lock);

> +

> +       kfree(path);

> +}

> +EXPORT_SYMBOL_GPL(icc_put);

> +

> +static struct icc_node *icc_node_create_nolock(int id)

> +{

> +       struct icc_node *node;

> +

> +       /* check if node already exists */

> +       node = node_find(id);

> +       if (node)

> +               goto out;

> +

> +       node = kzalloc(sizeof(*node), GFP_KERNEL);

> +       if (!node) {

> +               node = ERR_PTR(-ENOMEM);

> +               goto out;

> +       }

> +

> +       id = idr_alloc(&icc_idr, node, id, id + 1, GFP_KERNEL);

> +       if (WARN(id < 0, "couldn't get idr")) {

> +               kfree(node);

> +               node = ERR_PTR(id);

> +               goto out;

> +       }

> +

> +       node->id = id;

> +

> +out:

> +       return node;

> +}

> +

> +/**

> + * icc_node_create() - create a node

> + * @id: node id

> + *

> + * Return: icc_node pointer on success, or ERR_PTR() on error

> + */

> +struct icc_node *icc_node_create(int id)

> +{

> +       struct icc_node *node;

> +

> +       mutex_lock(&icc_lock);

> +

> +       node = icc_node_create_nolock(id);

> +

> +       mutex_unlock(&icc_lock);

> +

> +       return node;

> +}

> +EXPORT_SYMBOL_GPL(icc_node_create);

> +

> +/**

> + * icc_node_destroy() - destroy a node

> + * @id: node id

> + *

> + */

> +void icc_node_destroy(int id)

> +{

> +       struct icc_node *node;

> +

> +       node = node_find(id);

> +       if (node) {

> +               mutex_lock(&icc_lock);


mutex_lock should be moved above node_find, since node_find needs the lock held.

> +               idr_remove(&icc_idr, node->id);

> +               WARN_ON(!hlist_empty(&node->req_list));

> +               mutex_unlock(&icc_lock);

> +       }

> +

> +       kfree(node);

> +}

> +EXPORT_SYMBOL_GPL(icc_node_destroy);

> +

> +/**

> + * icc_link_create() - create a link between two nodes

> + * @src_id: source node id

> + * @dst_id: destination node id

> + *

> + * Create a link between two nodes. The nodes might belong to different

> + * interconnect providers and the @dst_id node might not exist (if the

> + * provider driver has not probed yet). So just create the @dst_id node

> + * and when the actual provider driver is probed, the rest of the node

> + * data is filled.

> + *

> + * Return: 0 on success, or an error code otherwise

> + */

> +int icc_link_create(struct icc_node *node, const int dst_id)

> +{

> +       struct icc_node *dst;

> +       struct icc_node **new;

> +       int ret = 0;

> +

> +       if (!node->provider)

> +               return -EINVAL;

> +

> +       mutex_lock(&icc_lock);

> +

> +       dst = node_find(dst_id);

> +       if (!dst) {

> +               dst = icc_node_create_nolock(dst_id);

> +

> +               if (IS_ERR(dst)) {

> +                       ret = PTR_ERR(dst);

> +                       goto out;

> +               }

> +       }

> +

> +       new = krealloc(node->links,

> +                      (node->num_links + 1) * sizeof(*node->links),

> +                      GFP_KERNEL);

> +       if (!new) {

> +               ret = -ENOMEM;

> +               goto out;

> +       }

> +

> +       node->links = new;

> +       node->links[node->num_links++] = dst;

> +

> +out:

> +       mutex_unlock(&icc_lock);

> +

> +       return ret;

> +}

> +EXPORT_SYMBOL_GPL(icc_link_create);

> +

> +/**

> + * icc_link_destroy() - destroy a link between two nodes

> + * @src: pointer to source node

> + * @dst: pointer to destination node

> + *

> + * Return: 0 on success, or an error code otherwise

> + */

> +int icc_link_destroy(struct icc_node *src, struct icc_node *dst)

> +{

> +       struct icc_node **new;

> +       struct icc_node *last;

> +       int ret = 0;

> +       size_t slot;

> +

> +       if (IS_ERR_OR_NULL(src))

> +               return -EINVAL;

> +

> +       if (IS_ERR_OR_NULL(dst))

> +               return -EINVAL;

> +

> +       mutex_lock(&icc_lock);

> +

> +       for (slot = 0; slot < src->num_links; slot++)

> +               if (src->links[slot] == dst)

> +                       break;

> +


How about a warning or failure if slot == src->num_links, meaning
someone is trying to tear down a link they never set up.

> +       last = src->links[src->num_links];


Shouldn't it be src->num_links - 1?

> +

> +       new = krealloc(src->links,

> +                      (src->num_links - 1) * sizeof(*src->links),

> +                      GFP_KERNEL);

> +       if (!new) {

> +               ret = -ENOMEM;

> +               goto out;


It's technically not really a problem if this realloc fails, right?
Your old array should still be valid, and it's big enough to hold
everything you wanted. Just only assign src->link = new if realloc
succeeds.

> +       }

> +

> +       src->links = new;

> +

> +       if (slot < src->num_links - 1)

> +               /* move the last element to the slot that was freed */

> +               src->links[slot] = last;


If you moved this above the realloc, then you could do away with the
conditional part of it, since at worst it would end up being:
src->links[num_links - 1] = src->links[num_links - 1]; which is a
no-op. You also wouldn't need the "last" local either.