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IPA — the networking datapath accelerator
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The **IPA (IP Accelerator)** is a hardware packet-processing engine that offloads
routing/filtering/NAT and per-flow DMA from the CPU. On a phone its main job is
the **cellular (WWAN/RMNET) datapath**; on this Wi-Fi-only e-reader that job is
dormant, but the IPA block is still present and firmware-loaded because it also
backs the **WLAN** and **USB-tethering** offload paths. This page separates what
is wired to live hardware from what is carried but idle. Facts from
``artifacts/boot_a/board.dts`` and ``kernel_config.txt``.

Hardware
========

- ``qcom,ipa`` — ``ipa-base`` **``0x1e00000``** (size ``0x84000``) + ``gsi-base``
  **``0x1e04000``** (size ``0x23000``); IRQs ``0x137``, ``0x1b0``. The **GSI**
  (Generic Software Interface) is IPA's event-ring/DMA front end.
- ``qcom,ipa-hw-ver = 0x12`` — an IPA v4-generation core; ``ipa-hw-mode = 0``
  (normal silicon, not emulation).
- **Firmware:** ``qcom,use-gsi-ipa-fw = "lagoon_ipa_fws"`` — the IPA/GSI
  microcode, loaded into the ``ipa_fw_region@0x8b700000`` / ``ipa_gsi_region``
  carve-outs (:doc:`/boot/base-dtb`).
- **SMMU isolation:** three context banks — ``ipa-smmu-ap-cb`` (AP),
  ``ipa-smmu-wlan-cb`` (WLAN), ``ipa-smmu-uc-cb`` (IPA microcontroller) — each an
  apps-SMMU stream (:doc:`/boot/base-dtb`).

Datapaths — live vs. dormant
============================

.. list-table::
   :header-rows: 1
   :widths: 26 16 58

   * - Path
     - Status
     - Evidence
   * - **Modem / RMNET** (WWAN)
     - **dormant**
     - ``qcom,rmnet-ipa3``, ``qcom,modem-cfg-emb-pipe-flt`` — the embedded modem
       pipe-filtering path; the modem is never brought up (no cellular RF,
       :doc:`/audio/dsp-firmware`)
   * - **WLAN offload** (WDI2)
     - **wired to live HW**
     - ``qcom,ipa-wdi2`` + ``qcom,ipa-wdi2_over_gsi`` + ``ipa-smmu-wlan-cb`` —
       the WLAN-to-IPA data interface for the active WCN3990 Wi-Fi
       (:doc:`/wireless/bluetooth`)
   * - **USB tethering** (RNDIS)
     - available
     - ``CONFIG_RNDIS_IPA=y`` — RNDIS-over-USB offload through IPA
       (:doc:`/boot/usb-transport`)
   * - **PCIe/MHI modem proxy**
     - off
     - ``CONFIG_IPA3_MHI_PROXY`` / ``MHI_PRIME_MANAGER`` **not set** — no external
       MHI modem

Kernel drivers: ``CONFIG_IPA3=y``, ``CONFIG_IPA_WDI_UNIFIED_API=y``,
``CONFIG_RMNET_IPA3=y``, ``CONFIG_RNDIS_IPA=y``. So the IPA core, its WLAN WDI
path and USB RNDIS path are all compiled in; only the cellular and MHI consumers
are inert.

Unlike the dormant modem stack elsewhere, this is not a pure reference-base
leftover: its WLAN WDI2 / RNDIS consumer config is compiled in and active,
though actual traffic through these paths was not directly observed.

Provenance
==========

:Source: ``artifacts/boot_a/board.dts`` (``qcom,ipa`` / ``qcom,rmnet-ipa3`` /
   ``ipa-smmu-*-cb`` nodes — addresses, IRQs, HW version, firmware name, features)
   and ``artifacts/boot_a/kernel_config.txt`` (IPA3 / WDI / RMNET / RNDIS / MHI
   selection).
:Method: DTB node reading and kernel-config cross-check. No code executed.
:Cross-refs: :doc:`/boot/base-dtb` (``ipa_fw_region`` / ``ipa_gsi_region`` carve-outs,
   SMMU), :doc:`/audio/dsp-firmware` (dormant modem/RMNET),
   :doc:`/wireless/bluetooth` (active WCN3990 WLAN), :doc:`/boot/usb-transport`
   (RNDIS tethering).