Adding upstream version 5.10.209.upstream/5.10.209upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 325 insertions, 0 deletions

diff --git a/Documentation/networking/device_drivers/ethernet/amazon/ena.rst b/Documentation/networking/device_drivers/ethernet/amazon/ena.rst
new file mode 100644
index 000000000..3561a8a29
--- /dev/null
+++ b/Documentation/networking/device_drivers/ethernet/amazon/ena.rst
@@ -0,0 +1,325 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+============================================================
+Linux kernel driver for Elastic Network Adapter (ENA) family
+============================================================
+
+Overview
+========
+
+ENA is a networking interface designed to make good use of modern CPU
+features and system architectures.
+
+The ENA device exposes a lightweight management interface with a
+minimal set of memory mapped registers and extendable command set
+through an Admin Queue.
+
+The driver supports a range of ENA devices, is link-speed independent
+(i.e., the same driver is used for 10GbE, 25GbE, 40GbE, etc.), and has
+a negotiated and extendable feature set.
+
+Some ENA devices support SR-IOV. This driver is used for both the
+SR-IOV Physical Function (PF) and Virtual Function (VF) devices.
+
+ENA devices enable high speed and low overhead network traffic
+processing by providing multiple Tx/Rx queue pairs (the maximum number
+is advertised by the device via the Admin Queue), a dedicated MSI-X
+interrupt vector per Tx/Rx queue pair, adaptive interrupt moderation,
+and CPU cacheline optimized data placement.
+
+The ENA driver supports industry standard TCP/IP offload features such
+as checksum offload and TCP transmit segmentation offload (TSO).
+Receive-side scaling (RSS) is supported for multi-core scaling.
+
+The ENA driver and its corresponding devices implement health
+monitoring mechanisms such as watchdog, enabling the device and driver
+to recover in a manner transparent to the application, as well as
+debug logs.
+
+Some of the ENA devices support a working mode called Low-latency
+Queue (LLQ), which saves several more microseconds.
+
+ENA Source Code Directory Structure
+===================================
+
+=================   ======================================================
+ena_com.[ch]        Management communication layer. This layer is
+		    responsible for the handling all the management
+		    (admin) communication between the device and the
+		    driver.
+ena_eth_com.[ch]    Tx/Rx data path.
+ena_admin_defs.h    Definition of ENA management interface.
+ena_eth_io_defs.h   Definition of ENA data path interface.
+ena_common_defs.h   Common definitions for ena_com layer.
+ena_regs_defs.h     Definition of ENA PCI memory-mapped (MMIO) registers.
+ena_netdev.[ch]     Main Linux kernel driver.
+ena_syfsfs.[ch]     Sysfs files.
+ena_ethtool.c       ethtool callbacks.
+ena_pci_id_tbl.h    Supported device IDs.
+=================   ======================================================
+
+Management Interface:
+=====================
+
+ENA management interface is exposed by means of:
+
+- PCIe Configuration Space
+- Device Registers
+- Admin Queue (AQ) and Admin Completion Queue (ACQ)
+- Asynchronous Event Notification Queue (AENQ)
+
+ENA device MMIO Registers are accessed only during driver
+initialization and are not involved in further normal device
+operation.
+
+AQ is used for submitting management commands, and the
+results/responses are reported asynchronously through ACQ.
+
+ENA introduces a small set of management commands with room for
+vendor-specific extensions. Most of the management operations are
+framed in a generic Get/Set feature command.
+
+The following admin queue commands are supported:
+
+- Create I/O submission queue
+- Create I/O completion queue
+- Destroy I/O submission queue
+- Destroy I/O completion queue
+- Get feature
+- Set feature
+- Configure AENQ
+- Get statistics
+
+Refer to ena_admin_defs.h for the list of supported Get/Set Feature
+properties.
+
+The Asynchronous Event Notification Queue (AENQ) is a uni-directional
+queue used by the ENA device to send to the driver events that cannot
+be reported using ACQ. AENQ events are subdivided into groups. Each
+group may have multiple syndromes, as shown below
+
+The events are:
+
+	====================	===============
+	Group			Syndrome
+	====================	===============
+	Link state change	**X**
+	Fatal error		**X**
+	Notification		Suspend traffic
+	Notification		Resume traffic
+	Keep-Alive		**X**
+	====================	===============
+
+ACQ and AENQ share the same MSI-X vector.
+
+Keep-Alive is a special mechanism that allows monitoring of the
+device's health. The driver maintains a watchdog (WD) handler which,
+if fired, logs the current state and statistics then resets and
+restarts the ENA device and driver. A Keep-Alive event is delivered by
+the device every second. The driver re-arms the WD upon reception of a
+Keep-Alive event. A missed Keep-Alive event causes the WD handler to
+fire.
+
+Data Path Interface
+===================
+I/O operations are based on Tx and Rx Submission Queues (Tx SQ and Rx
+SQ correspondingly). Each SQ has a completion queue (CQ) associated
+with it.
+
+The SQs and CQs are implemented as descriptor rings in contiguous
+physical memory.
+
+The ENA driver supports two Queue Operation modes for Tx SQs:
+
+- Regular mode
+
+  * In this mode the Tx SQs reside in the host's memory. The ENA
+    device fetches the ENA Tx descriptors and packet data from host
+    memory.
+
+- Low Latency Queue (LLQ) mode or "push-mode".
+
+  * In this mode the driver pushes the transmit descriptors and the
+    first 128 bytes of the packet directly to the ENA device memory
+    space. The rest of the packet payload is fetched by the
+    device. For this operation mode, the driver uses a dedicated PCI
+    device memory BAR, which is mapped with write-combine capability.
+
+The Rx SQs support only the regular mode.
+
+Note: Not all ENA devices support LLQ, and this feature is negotiated
+      with the device upon initialization. If the ENA device does not
+      support LLQ mode, the driver falls back to the regular mode.
+
+The driver supports multi-queue for both Tx and Rx. This has various
+benefits:
+
+- Reduced CPU/thread/process contention on a given Ethernet interface.
+- Cache miss rate on completion is reduced, particularly for data
+  cache lines that hold the sk_buff structures.
+- Increased process-level parallelism when handling received packets.
+- Increased data cache hit rate, by steering kernel processing of
+  packets to the CPU, where the application thread consuming the
+  packet is running.
+- In hardware interrupt re-direction.
+
+Interrupt Modes
+===============
+The driver assigns a single MSI-X vector per queue pair (for both Tx
+and Rx directions). The driver assigns an additional dedicated MSI-X vector
+for management (for ACQ and AENQ).
+
+Management interrupt registration is performed when the Linux kernel
+probes the adapter, and it is de-registered when the adapter is
+removed. I/O queue interrupt registration is performed when the Linux
+interface of the adapter is opened, and it is de-registered when the
+interface is closed.
+
+The management interrupt is named::
+
+   ena-mgmnt@pci:<PCI domain:bus:slot.function>
+
+and for each queue pair, an interrupt is named::
+
+   <interface name>-Tx-Rx-<queue index>
+
+The ENA device operates in auto-mask and auto-clear interrupt
+modes. That is, once MSI-X is delivered to the host, its Cause bit is
+automatically cleared and the interrupt is masked. The interrupt is
+unmasked by the driver after NAPI processing is complete.
+
+Interrupt Moderation
+====================
+ENA driver and device can operate in conventional or adaptive interrupt
+moderation mode.
+
+In conventional mode the driver instructs device to postpone interrupt
+posting according to static interrupt delay value. The interrupt delay
+value can be configured through ethtool(8). The following ethtool
+parameters are supported by the driver: tx-usecs, rx-usecs
+
+In adaptive interrupt moderation mode the interrupt delay value is
+updated by the driver dynamically and adjusted every NAPI cycle
+according to the traffic nature.
+
+Adaptive coalescing can be switched on/off through ethtool(8)
+adaptive_rx on|off parameter.
+
+More information about Adaptive Interrupt Moderation (DIM) can be found in
+Documentation/networking/net_dim.rst
+
+RX copybreak
+============
+The rx_copybreak is initialized by default to ENA_DEFAULT_RX_COPYBREAK
+and can be configured by the ETHTOOL_STUNABLE command of the
+SIOCETHTOOL ioctl.
+
+SKB
+===
+The driver-allocated SKB for frames received from Rx handling using
+NAPI context. The allocation method depends on the size of the packet.
+If the frame length is larger than rx_copybreak, napi_get_frags()
+is used, otherwise netdev_alloc_skb_ip_align() is used, the buffer
+content is copied (by CPU) to the SKB, and the buffer is recycled.
+
+Statistics
+==========
+The user can obtain ENA device and driver statistics using ethtool.
+The driver can collect regular or extended statistics (including
+per-queue stats) from the device.
+
+In addition the driver logs the stats to syslog upon device reset.
+
+MTU
+===
+The driver supports an arbitrarily large MTU with a maximum that is
+negotiated with the device. The driver configures MTU using the
+SetFeature command (ENA_ADMIN_MTU property). The user can change MTU
+via ip(8) and similar legacy tools.
+
+Stateless Offloads
+==================
+The ENA driver supports:
+
+- TSO over IPv4/IPv6
+- TSO with ECN
+- IPv4 header checksum offload
+- TCP/UDP over IPv4/IPv6 checksum offloads
+
+RSS
+===
+- The ENA device supports RSS that allows flexible Rx traffic
+  steering.
+- Toeplitz and CRC32 hash functions are supported.
+- Different combinations of L2/L3/L4 fields can be configured as
+  inputs for hash functions.
+- The driver configures RSS settings using the AQ SetFeature command
+  (ENA_ADMIN_RSS_HASH_FUNCTION, ENA_ADMIN_RSS_HASH_INPUT and
+  ENA_ADMIN_RSS_INDIRECTION_TABLE_CONFIG properties).
+- If the NETIF_F_RXHASH flag is set, the 32-bit result of the hash
+  function delivered in the Rx CQ descriptor is set in the received
+  SKB.
+- The user can provide a hash key, hash function, and configure the
+  indirection table through ethtool(8).
+
+DATA PATH
+=========
+Tx
+--
+
+end_start_xmit() is called by the stack. This function does the following:
+
+- Maps data buffers (skb->data and frags).
+- Populates ena_buf for the push buffer (if the driver and device are
+  in push mode.)
+- Prepares ENA bufs for the remaining frags.
+- Allocates a new request ID from the empty req_id ring. The request
+  ID is the index of the packet in the Tx info. This is used for
+  out-of-order TX completions.
+- Adds the packet to the proper place in the Tx ring.
+- Calls ena_com_prepare_tx(), an ENA communication layer that converts
+  the ena_bufs to ENA descriptors (and adds meta ENA descriptors as
+  needed.)
+
+  * This function also copies the ENA descriptors and the push buffer
+    to the Device memory space (if in push mode.)
+
+- Writes doorbell to the ENA device.
+- When the ENA device finishes sending the packet, a completion
+  interrupt is raised.
+- The interrupt handler schedules NAPI.
+- The ena_clean_tx_irq() function is called. This function handles the
+  completion descriptors generated by the ENA, with a single
+  completion descriptor per completed packet.
+
+  * req_id is retrieved from the completion descriptor. The tx_info of
+    the packet is retrieved via the req_id. The data buffers are
+    unmapped and req_id is returned to the empty req_id ring.
+  * The function stops when the completion descriptors are completed or
+    the budget is reached.
+
+Rx
+--
+
+- When a packet is received from the ENA device.
+- The interrupt handler schedules NAPI.
+- The ena_clean_rx_irq() function is called. This function calls
+  ena_rx_pkt(), an ENA communication layer function, which returns the
+  number of descriptors used for a new unhandled packet, and zero if
+  no new packet is found.
+- Then it calls the ena_clean_rx_irq() function.
+- ena_eth_rx_skb() checks packet length:
+
+  * If the packet is small (len < rx_copybreak), the driver allocates
+    a SKB for the new packet, and copies the packet payload into the
+    SKB data buffer.
+
+    - In this way the original data buffer is not passed to the stack
+      and is reused for future Rx packets.
+
+  * Otherwise the function unmaps the Rx buffer, then allocates the
+    new SKB structure and hooks the Rx buffer to the SKB frags.
+
+- The new SKB is updated with the necessary information (protocol,
+  checksum hw verify result, etc.), and then passed to the network
+  stack, using the NAPI interface function napi_gro_receive().