@@ -0,0 +1,142 @@
+.. SPDX-License-Identifier: GPL-2.0-only OR MIT
+
+====================================================
+Texas Instruments NPAC (Network Packet ACcelerator)
+====================================================
+
+Overview
+========
+
+NPAC (Network Packet ACcelerator) is a hardware accelerator available
+on Texas Instruments SoCs in the TDA5 family that provides network packet
+processing acceleration [0]_.
+
+The NPAC Host Driver runs on a dedicated remote processor and manages
+NPAC hardware.
+
+The NPAC client driver provides offloading support for ethernet-related tasks
+and communicates with the NPAC Host Driver over RPMsg (Remote Processor
+Messaging).
+
+The driver exposes /dev/accel/accel* as the userspace interface for accelerator
+configuration and management operations.
+
+The NPAC Host Driver supports ACL (Access Control
+List) [1]_ rule offload. ACL configuration requests are sent by the client
+driver to the NPAC Host Driver.
+
+Communication Model
+-------------------
+
+The NPAC client driver registers with the RPMsg subsystem during driver
+initialization.
+
+When the NPAC host driver announces the NPAC RPMsg service endpoint, the
+RPMsg core matches the announced service against the registered NPAC client
+driver and invokes the driver probe callback.
+
+Offload command received from userspace are formatted into RPMsgs and sent
+to the NPAC Host Driver.
+
+NPAC Host Driver responses are received through RPMsg callbacks.
+
+ACL Rule Offload
+----------------
+
+ACL (Access Control List) rules are packet filtering policies that define how
+network traffic should be handled — for example, dropping packets from a
+blacklisted source IP or allowing traffic only from trusted MAC addresses.
+
+In the standard Linux networking stack, ACL enforcement is handled in software
+by the netfilter subsystem. Each packet is inspected against the configured
+ruleset on the host CPU. On embedded SoCs in the TDA5 family such as TDA54,
+the per-packet overhead of software-based ACL enforcement accumulates under
+high traffic rates, increasing CPU utilization and reducing the processing
+capacity available for other system functions.
+
+The NPAC client driver offloads rules from Linux to NPAC hardware.
+Once a rule is programmed, matching packets are handled entirely by NPAC,
+reducing CPU load.
+
+For example, a rule to drop all packets from a specific source IP or to
+allow packets from a trusted source is offloaded to NPAC. Instead of the
+host parsing each packet and applying the ACL rules, NPAC enforces the
+rule directly in hardware.
+
+Userspace Interface
+-------------------
+
+The driver exposes /dev/accel/accel* as the userspace control interface for ACL
+rule management operations.
+
+The interface uses IOCTL-based request handling for accelerator configuration
+and rule management operations.
+
+IOCTL Commands
+~~~~~~~~~~~~~~
+
+DRM_IOCTL_NPAC_ACL_ADD_RULE
+
+  This IOCTL allows userspace to add an ACL rule to the accelerator. The
+  call will forward the rule to the NPAC host driver for hardware programming.
+  The NPAC Host Driver is responsible for validating the rule and applying it to
+  the NPAC hardware.
+
+DRM_IOCTL_NPAC_ACL_DELETE_RULE
+
+  This IOCTL allows userspace to remove an ACL rule from the accelerator.
+  The call will forward the deletion request to the NPAC host driver, which
+  will remove the rule from the NPAC hardware.
+
+Driver Lifecycle
+----------------
+
+The driver lifecycle is coordinated through the RPMsg framework.
+
+Probe Flow
+~~~~~~~~~~
+
+1. The NPAC client driver registers with the RPMsg subsystem
+
+2. NPAC host driver initializes on the remote processor
+
+3. NPAC Host Driver announces its RPMsg service endpoint
+
+4. The RPMsg subsystem in Linux matches the announced service against
+   the registered NPAC client driver
+
+5. The RPMsg subsystem invokes the driver probe callback
+
+6. Driver communication resources are initialized
+
+7. /dev/accel/accel* becomes available to userspace
+
+Request Flow
+~~~~~~~~~~~~
+
+1. Userspace submits an ACL configuration request through /dev/accel/accel*
+
+2. The request is forwarded to the NPAC host driver using RPMsg
+
+3. The NPAC Host Driver validates the request and performs the required hardware
+   programming operations
+
+4. NPAC Host Driver responses are received by the Linux driver through the RPMsg
+   callback.
+
+RPMsg Integration
+-----------------
+
+The driver integrates with the Linux RPMsg subsystem for communication with
+the NPAC host driver processor.
+
+RPMsg is used as the transport mechanism for:
+
+- Accelerator configuration requests
+- NPAC Host Driver responses
+
+References
+----------
+
+.. [0] https://www.ti.com/lit/ds/symlink/tda54-q1.pdf
+.. [1] https://en.wikipedia.org/wiki/Access-control_list#Networking_ACLs