[PATCH net-next V4 02/14] documentation: networking: add shared devlink documentation

[Tariq Toukan <tariqt@nvidia.com>]

From: Jiri Pirko <jiri@nvidia.com>

Document shared devlink instances for multiple PFs on the same chip.

Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Reviewed-by: Cosmin Ratiu <cratiu@nvidia.com>
Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
---
 .../networking/devlink/devlink-shared.rst     | 66 +++++++++++++++++++
 Documentation/networking/devlink/index.rst    |  1 +
 2 files changed, 67 insertions(+)
 create mode 100644 Documentation/networking/devlink/devlink-shared.rst

diff --git a/Documentation/networking/devlink/devlink-shared.rst b/Documentation/networking/devlink/devlink-shared.rst
new file mode 100644
index 000000000000..be9dd6f295df
--- /dev/null
+++ b/Documentation/networking/devlink/devlink-shared.rst
@@ -0,0 +1,66 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+============================
+Devlink Shared Instances
+============================
+
+Overview
+========
+
+Shared devlink instances allow multiple physical functions (PFs) on the same
+chip to share an additional devlink instance for chip-wide operations. This
+should be implemented within individual drivers alongside the individual PF
+devlink instances, not replacing them.
+
+The shared devlink instance should be backed by a faux device and should
+provide a common interface for operations that affect the entire chip
+rather than individual PFs.
+
+Implementation
+==============
+
+Architecture
+------------
+
+The implementation should use:
+
+* **Faux device**: Virtual device backing the shared devlink instance
+* **Chip identification**: PFs are grouped by chip using a driver-specific identifier
+* **Shared instance management**: Global list of shared instances with reference counting
+
+Initialization Flow
+-------------------
+
+1. **PF calls shared devlink init** during driver probe
+2. **Chip identification** using driver-specific method to determine device identity
+3. **Lookup existing shared instance** for this chip identifier
+4. **Create new shared instance** if none exists:
+
+   * Create faux device with chip identifier as name
+   * Allocate and register devlink instance
+   * Add to global shared instances list
+
+5. **Add PF to shared instance** PF list
+6. **Set nested devlink instance** for the PF devlink instance
+
+Cleanup Flow
+------------
+
+1. **Cleanup** when PF is removed; destroy shared instance when last PF is removed
+
+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 VPD serial numbers,
+device tree properties, or other hardware-specific identifiers.
+
+Locking
+-------
+
+A global per-driver mutex protects the shared instances list and individual shared
+instance PF lists 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.
diff --git a/Documentation/networking/devlink/index.rst b/Documentation/networking/devlink/index.rst
index 35b12a2bfeba..f7ba7dcf477d 100644
--- a/Documentation/networking/devlink/index.rst
+++ b/Documentation/networking/devlink/index.rst
@@ -68,6 +68,7 @@ general.
    devlink-resource
    devlink-selftests
    devlink-trap
+   devlink-shared
 
 Driver-specific documentation
 -----------------------------
-- 
2.31.1