Devlink Shared Instances

Overview

Shared devlink instances allow multiple physical functions (PFs) on the same chip to share a devlink instance for chip-wide operations.

Multiple PFs may reside on the same physical chip, running a single firmware. Some of the resources and configurations may be shared among these PFs. The shared devlink instance provides an object to pin configuration knobs on.

There are two possible usage models:

1. The shared devlink instance is used alongside individual PF devlink instances, providing chip-wide configuration in addition to per-PF configuration.

2. The shared devlink instance is the only devlink instance, without per-PF instances.

It is up to the driver to decide which usage model to use.

The shared devlink instance is not backed by any struct device.

Implementation

Architecture

The implementation uses:

• Chip identification: PFs are grouped by chip using a driver-specific identifier

• Shared instance management: Global list of shared instances with reference counting

API Functions

The following functions are provided for managing shared devlink instances:

• devlink_shd_get(): Get or create a shared devlink instance identified by a string ID

• devlink_shd_put(): Release a reference on a shared devlink instance

• devlink_shd_get_priv(): Get private data from shared devlink instance

Initialization Flow

1. PF calls shared devlink init during driver probe

2. Chip identification using driver-specific method to determine device identity

3. Get or create shared instance using devlink_shd_get():

   • The function looks up existing instance by identifier

   • If none exists, creates new instance: - Allocates and registers devlink instance - Adds to global shared instances list - Increments reference count

4. Set nested devlink instance for the PF devlink instance using devl_nested_devlink_set() before registering the PF devlink instance

Cleanup Flow

1. Cleanup when PF is removed

2. Call devlink_shd_put() to release reference (decrements reference count)

3. Shared instance is automatically destroyed when the last PF removes (reference count reaches zero)

Chip Identification

PFs belonging to the same chip are identified using a driver-specific method. The driver is free to choose any identifier that is suitable for determining whether two PFs are part of the same device. Examples include:

• PCI VPD serial numbers: Extract from PCI VPD

• Device tree properties: Read chip identifier from device tree

• Other hardware-specific identifiers: Any unique identifier that groups PFs by chip

Locking

A global mutex (shd_mutex) protects the shared instances list during registration/deregistration.

Similarly to other nested devlink instance relationships, devlink lock of the shared instance should be always taken after the devlink lock of PF.

Reference Counting

Each shared devlink instance maintains a reference count (refcount_t refcount). The reference count is incremented when devlink_shd_get() is called and decremented when devlink_shd_put() is called. When the reference count reaches zero, the shared instance is automatically destroyed.