net: ena: Add a driver for Amazon Elastic Network Adapters (ENA)

This is a driver for the ENA family of networking devices.

Signed-off-by: Netanel Belgazal <netanel@annapurnalabs.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 307 insertions, 0 deletions

diff --git a/Documentation/networking/00-INDEX b/Documentation/networking/00-INDEX
index 415154a487d0..a7697783ac4c 100644
--- a/Documentation/networking/00-INDEX
+++ b/Documentation/networking/00-INDEX
@@ -74,6 +74,8 @@ dns_resolver.txt
         - The DNS resolver module allows kernel servies to make DNS queries.
 driver.txt
         - Softnet driver issues.
+ena.txt
+        - info on Amazon's Elastic Network Adapter (ENA)
 e100.txt
         - info on Intel's EtherExpress PRO/100 line of 10/100 boards
 e1000.txt
diff --git a/Documentation/networking/ena.txt b/Documentation/networking/ena.txt
new file mode 100644
index 000000000000..2b4b6f57e549
--- /dev/null
+++ b/Documentation/networking/ena.txt
@@ -0,0 +1,305 @@
+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.
+
+Supported PCI vendor ID/device IDs:
+===================================
+1d0f:0ec2 - ENA PF
+1d0f:1ec2 - ENA PF with LLQ support
+1d0f:ec20 - ENA VF
+1d0f:ec21 - ENA VF with LLQ support
+
+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 very 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.
+
+By default ENA driver applies adaptive coalescing on Rx traffic and
+conventional coalescing on Tx traffic.
+
+Adaptive coalescing can be switched on/off through ethtool(8)
+adaptive_rx on|off parameter.
+
+The driver chooses interrupt delay value according to the number of
+bytes and packets received between interrupt unmasking and interrupt
+posting. The driver uses interrupt delay table that subdivides the
+range of received bytes/packets into 5 levels and assigns interrupt
+delay value to each level.
+
+The user can enable/disable adaptive moderation, modify the interrupt
+delay table and restore its default values through sysfs.
+
+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_REDIRECTION_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().