accel/qaic: Add documentation for AIC100 accelerator driver

The Qualcomm Cloud AI 100 (AIC100) device is an Artificial Intelligence
accelerator PCIe card. It contains a number of components both in the
SoC and on the card which facilitate running workloads:

QSM: management processor
NSPs: workload compute units
DMA Bridge: dedicated data mover for the workloads
MHI: multiplexed communication channels
DDR: workload storage and memory

The Linux kernel driver for AIC100 is called "QAIC" and is located in the
accel subsystem.

Signed-off-by: Jeffrey Hugo <quic_jhugo@quicinc.com>
Reviewed-by: Carl Vanderlip <quic_carlv@quicinc.com>
Reviewed-by: Pranjal Ramajor Asha Kanojiya <quic_pkanojiy@quicinc.com>
Reviewed-by: Stanislaw Gruszka <stanislaw.gruszka@linux.intel.com>
Reviewed-by: Jacek Lawrynowicz <jacek.lawrynowicz@linux.intel.com>
Acked-by: Oded Gabbay <ogabbay@kernel.org>
Signed-off-by: Jacek Lawrynowicz <jacek.lawrynowicz@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1679932497-30277-2-git-send-email-quic_jhugo@quicinc.com

4 files changed, 694 insertions, 0 deletions

diff --git a/Documentation/accel/index.rst b/Documentation/accel/index.rst
index 2b43c9a7f67b..e94a0160b6a0 100644
--- a/Documentation/accel/index.rst
+++ b/Documentation/accel/index.rst
@@ -8,6 +8,7 @@ Compute Accelerators
    :maxdepth: 1
 
    introduction
+   qaic/index
 
 .. only::  subproject and html
 
diff --git a/Documentation/accel/qaic/aic100.rst b/Documentation/accel/qaic/aic100.rst
new file mode 100644
index 000000000000..c80d0f1307db
--- /dev/null
+++ b/Documentation/accel/qaic/aic100.rst
@@ -0,0 +1,510 @@
+.. SPDX-License-Identifier: GPL-2.0-only
+
+===============================
+ Qualcomm Cloud AI 100 (AIC100)
+===============================
+
+Overview
+========
+
+The Qualcomm Cloud AI 100/AIC100 family of products (including SA9000P - part of
+Snapdragon Ride) are PCIe adapter cards which contain a dedicated SoC ASIC for
+the purpose of efficiently running Artificial Intelligence (AI) Deep Learning
+inference workloads. They are AI accelerators.
+
+The PCIe interface of AIC100 is capable of PCIe Gen4 speeds over eight lanes
+(x8). An individual SoC on a card can have up to 16 NSPs for running workloads.
+Each SoC has an A53 management CPU. On card, there can be up to 32 GB of DDR.
+
+Multiple AIC100 cards can be hosted in a single system to scale overall
+performance. AIC100 cards are multi-user capable and able to execute workloads
+from multiple users in a concurrent manner.
+
+Hardware Description
+====================
+
+An AIC100 card consists of an AIC100 SoC, on-card DDR, and a set of misc
+peripherals (PMICs, etc).
+
+An AIC100 card can either be a PCIe HHHL form factor (a traditional PCIe card),
+or a Dual M.2 card. Both use PCIe to connect to the host system.
+
+As a PCIe endpoint/adapter, AIC100 uses the standard VendorID(VID)/
+DeviceID(DID) combination to uniquely identify itself to the host. AIC100
+uses the standard Qualcomm VID (0x17cb). All AIC100 SKUs use the same
+AIC100 DID (0xa100).
+
+AIC100 does not implement FLR (function level reset).
+
+AIC100 implements MSI but does not implement MSI-X. AIC100 requires 17 MSIs to
+operate (1 for MHI, 16 for the DMA Bridge).
+
+As a PCIe device, AIC100 utilizes BARs to provide host interfaces to the device
+hardware. AIC100 provides 3, 64-bit BARs.
+
+* The first BAR is 4K in size, and exposes the MHI interface to the host.
+
+* The second BAR is 2M in size, and exposes the DMA Bridge interface to the
+  host.
+
+* The third BAR is variable in size based on an individual AIC100's
+  configuration, but defaults to 64K. This BAR currently has no purpose.
+
+From the host perspective, AIC100 has several key hardware components -
+
+* MHI (Modem Host Interface)
+* QSM (QAIC Service Manager)
+* NSPs (Neural Signal Processor)
+* DMA Bridge
+* DDR
+
+MHI
+---
+
+AIC100 has one MHI interface over PCIe. MHI itself is documented at
+Documentation/mhi/index.rst MHI is the mechanism the host uses to communicate
+with the QSM. Except for workload data via the DMA Bridge, all interaction with
+the device occurs via MHI.
+
+QSM
+---
+
+QAIC Service Manager. This is an ARM A53 CPU that runs the primary
+firmware of the card and performs on-card management tasks. It also
+communicates with the host via MHI. Each AIC100 has one of
+these.
+
+NSP
+---
+
+Neural Signal Processor. Each AIC100 has up to 16 of these. These are
+the processors that run the workloads on AIC100. Each NSP is a Qualcomm Hexagon
+(Q6) DSP with HVX and HMX. Each NSP can only run one workload at a time, but
+multiple NSPs may be assigned to a single workload. Since each NSP can only run
+one workload, AIC100 is limited to 16 concurrent workloads. Workload
+"scheduling" is under the purview of the host. AIC100 does not automatically
+timeslice.
+
+DMA Bridge
+----------
+
+The DMA Bridge is custom DMA engine that manages the flow of data
+in and out of workloads. AIC100 has one of these. The DMA Bridge has 16
+channels, each consisting of a set of request/response FIFOs. Each active
+workload is assigned a single DMA Bridge channel. The DMA Bridge exposes
+hardware registers to manage the FIFOs (head/tail pointers), but requires host
+memory to store the FIFOs.
+
+DDR
+---
+
+AIC100 has on-card DDR. In total, an AIC100 can have up to 32 GB of DDR.
+This DDR is used to store workloads, data for the workloads, and is used by the
+QSM for managing the device. NSPs are granted access to sections of the DDR by
+the QSM. The host does not have direct access to the DDR, and must make
+requests to the QSM to transfer data to the DDR.
+
+High-level Use Flow
+===================
+
+AIC100 is a multi-user, programmable accelerator typically used for running
+neural networks in inferencing mode to efficiently perform AI operations.
+AIC100 is not intended for training neural networks. AIC100 can be utilized
+for generic compute workloads.
+
+Assuming a user wants to utilize AIC100, they would follow these steps:
+
+1. Compile the workload into an ELF targeting the NSP(s)
+2. Make requests to the QSM to load the workload and related artifacts into the
+   device DDR
+3. Make a request to the QSM to activate the workload onto a set of idle NSPs
+4. Make requests to the DMA Bridge to send input data to the workload to be
+   processed, and other requests to receive processed output data from the
+   workload.
+5. Once the workload is no longer required, make a request to the QSM to
+   deactivate the workload, thus putting the NSPs back into an idle state.
+6. Once the workload and related artifacts are no longer needed for future
+   sessions, make requests to the QSM to unload the data from DDR. This frees
+   the DDR to be used by other users.
+
+
+Boot Flow
+=========
+
+AIC100 uses a flashless boot flow, derived from Qualcomm MSMs.
+
+When AIC100 is first powered on, it begins executing PBL (Primary Bootloader)
+from ROM. PBL enumerates the PCIe link, and initializes the BHI (Boot Host
+Interface) component of MHI.
+
+Using BHI, the host points PBL to the location of the SBL (Secondary Bootloader)
+image. The PBL pulls the image from the host, validates it, and begins
+execution of SBL.
+
+SBL initializes MHI, and uses MHI to notify the host that the device has entered
+the SBL stage. SBL performs a number of operations:
+
+* SBL initializes the majority of hardware (anything PBL left uninitialized),
+  including DDR.
+* SBL offloads the bootlog to the host.
+* SBL synchronizes timestamps with the host for future logging.
+* SBL uses the Sahara protocol to obtain the runtime firmware images from the
+  host.
+
+Once SBL has obtained and validated the runtime firmware, it brings the NSPs out
+of reset, and jumps into the QSM.
+
+The QSM uses MHI to notify the host that the device has entered the QSM stage
+(AMSS in MHI terms). At this point, the AIC100 device is fully functional, and
+ready to process workloads.
+
+Userspace components
+====================
+
+Compiler
+--------
+
+An open compiler for AIC100 based on upstream LLVM can be found at:
+https://github.com/quic/software-kit-for-qualcomm-cloud-ai-100-cc
+
+Usermode Driver (UMD)
+---------------------
+
+An open UMD that interfaces with the qaic kernel driver can be found at:
+https://github.com/quic/software-kit-for-qualcomm-cloud-ai-100
+
+Sahara loader
+-------------
+
+An open implementation of the Sahara protocol called kickstart can be found at:
+https://github.com/andersson/qdl
+
+MHI Channels
+============
+
+AIC100 defines a number of MHI channels for different purposes. This is a list
+of the defined channels, and their uses.
+
++----------------+---------+----------+----------------------------------------+
+| Channel name   | IDs     | EEs      | Purpose                                |
++================+=========+==========+========================================+
+| QAIC_LOOPBACK  | 0 & 1   | AMSS     | Any data sent to the device on this    |
+|                |         |          | channel is sent back to the host.      |
++----------------+---------+----------+----------------------------------------+
+| QAIC_SAHARA    | 2 & 3   | SBL      | Used by SBL to obtain the runtime      |
+|                |         |          | firmware from the host.                |
++----------------+---------+----------+----------------------------------------+
+| QAIC_DIAG      | 4 & 5   | AMSS     | Used to communicate with QSM via the   |
+|                |         |          | DIAG protocol.                         |
++----------------+---------+----------+----------------------------------------+
+| QAIC_SSR       | 6 & 7   | AMSS     | Used to notify the host of subsystem   |
+|                |         |          | restart events, and to offload SSR     |
+|                |         |          | crashdumps.                            |
++----------------+---------+----------+----------------------------------------+
+| QAIC_QDSS      | 8 & 9   | AMSS     | Used for the Qualcomm Debug Subsystem. |
++----------------+---------+----------+----------------------------------------+
+| QAIC_CONTROL   | 10 & 11 | AMSS     | Used for the Neural Network Control    |
+|                |         |          | (NNC) protocol. This is the primary    |
+|                |         |          | channel between host and QSM for       |
+|                |         |          | managing workloads.                    |
++----------------+---------+----------+----------------------------------------+
+| QAIC_LOGGING   | 12 & 13 | SBL      | Used by the SBL to send the bootlog to |
+|                |         |          | the host.                              |
++----------------+---------+----------+----------------------------------------+
+| QAIC_STATUS    | 14 & 15 | AMSS     | Used to notify the host of Reliability,|
+|                |         |          | Accessibility, Serviceability (RAS)    |
+|                |         |          | events.                                |
++----------------+---------+----------+----------------------------------------+
+| QAIC_TELEMETRY | 16 & 17 | AMSS     | Used to get/set power/thermal/etc      |
+|                |         |          | attributes.                            |
++----------------+---------+----------+----------------------------------------+
+| QAIC_DEBUG     | 18 & 19 | AMSS     | Not used.                              |
++----------------+---------+----------+----------------------------------------+
+| QAIC_TIMESYNC  | 20 & 21 | SBL/AMSS | Used to synchronize timestamps in the  |
+|                |         |          | device side logs with the host time    |
+|                |         |          | source.                                |
++----------------+---------+----------+----------------------------------------+
+
+DMA Bridge
+==========
+
+Overview
+--------
+
+The DMA Bridge is one of the main interfaces to the host from the device
+(the other being MHI). As part of activating a workload to run on NSPs, the QSM
+assigns that network a DMA Bridge channel. A workload's DMA Bridge channel
+(DBC for short) is solely for the use of that workload and is not shared with
+other workloads.
+
+Each DBC is a pair of FIFOs that manage data in and out of the workload. One
+FIFO is the request FIFO. The other FIFO is the response FIFO.
+
+Each DBC contains 4 registers in hardware:
+
+* Request FIFO head pointer (offset 0x0). Read only by the host. Indicates the
+  latest item in the FIFO the device has consumed.
+* Request FIFO tail pointer (offset 0x4). Read/write by the host. Host
+  increments this register to add new items to the FIFO.
+* Response FIFO head pointer (offset 0x8). Read/write by the host. Indicates
+  the latest item in the FIFO the host has consumed.
+* Response FIFO tail pointer (offset 0xc). Read only by the host. Device
+  increments this register to add new items to the FIFO.
+
+The values in each register are indexes in the FIFO. To get the location of the
+FIFO element pointed to by the register: FIFO base address + register * element
+size.
+
+DBC registers are exposed to the host via the second BAR. Each DBC consumes
+4KB of space in the BAR.
+
+The actual FIFOs are backed by host memory. When sending a request to the QSM
+to activate a network, the host must donate memory to be used for the FIFOs.
+Due to internal mapping limitations of the device, a single contiguous chunk of
+memory must be provided per DBC, which hosts both FIFOs. The request FIFO will
+consume the beginning of the memory chunk, and the response FIFO will consume
+the end of the memory chunk.
+
+Request FIFO
+------------
+
+A request FIFO element has the following structure:
+
+.. code-block:: c
+
+  struct request_elem {
+	u16 req_id;
+	u8  seq_id;
+	u8  pcie_dma_cmd;
+	u32 reserved;
+	u64 pcie_dma_source_addr;
+	u64 pcie_dma_dest_addr;
+	u32 pcie_dma_len;
+	u32 reserved;
+	u64 doorbell_addr;
+	u8  doorbell_attr;
+	u8  reserved;
+	u16 reserved;
+	u32 doorbell_data;
+	u32 sem_cmd0;
+	u32 sem_cmd1;
+	u32 sem_cmd2;
+	u32 sem_cmd3;
+  };
+
+Request field descriptions:
+
+req_id
+	request ID. A request FIFO element and a response FIFO element with
+	the same request ID refer to the same command.
+
+seq_id
+	sequence ID within a request. Ignored by the DMA Bridge.
+
+pcie_dma_cmd
+	describes the DMA element of this request.
+
+	* Bit(7) is the force msi flag, which overrides the DMA Bridge MSI logic
+	  and generates a MSI when this request is complete, and QSM
+	  configures the DMA Bridge to look at this bit.
+	* Bits(6:5) are reserved.
+	* Bit(4) is the completion code flag, and indicates that the DMA Bridge
+	  shall generate a response FIFO element when this request is
+	  complete.
+	* Bit(3) indicates if this request is a linked list transfer(0) or a bulk
+	  transfer(1).
+	* Bit(2) is reserved.
+	* Bits(1:0) indicate the type of transfer. No transfer(0), to device(1),
+	  from device(2). Value 3 is illegal.
+
+pcie_dma_source_addr
+	source address for a bulk transfer, or the address of the linked list.
+
+pcie_dma_dest_addr
+	destination address for a bulk transfer.
+
+pcie_dma_len
+	length of the bulk transfer. Note that the size of this field
+	limits transfers to 4G in size.
+
+doorbell_addr
+	address of the doorbell to ring when this request is complete.
+
+doorbell_attr
+	doorbell attributes.
+
+	* Bit(7) indicates if a write to a doorbell is to occur.
+	* Bits(6:2) are reserved.
+	* Bits(1:0) contain the encoding of the doorbell length. 0 is 32-bit,
+	  1 is 16-bit, 2 is 8-bit, 3 is reserved. The doorbell address
+	  must be naturally aligned to the specified length.
+
+doorbell_data
+	data to write to the doorbell. Only the bits corresponding to
+	the doorbell length are valid.
+
+sem_cmdN
+	semaphore command.
+
+	* Bit(31) indicates this semaphore command is enabled.
+	* Bit(30) is the to-device DMA fence. Block this request until all
+	  to-device DMA transfers are complete.
+	* Bit(29) is the from-device DMA fence. Block this request until all
+	  from-device DMA transfers are complete.
+	* Bits(28:27) are reserved.
+	* Bits(26:24) are the semaphore command. 0 is NOP. 1 is init with the
+	  specified value. 2 is increment. 3 is decrement. 4 is wait
+	  until the semaphore is equal to the specified value. 5 is wait
+	  until the semaphore is greater or equal to the specified value.
+	  6 is "P", wait until semaphore is greater than 0, then
+	  decrement by 1. 7 is reserved.
+	* Bit(23) is reserved.
+	* Bit(22) is the semaphore sync. 0 is post sync, which means that the
+	  semaphore operation is done after the DMA transfer. 1 is
+	  presync, which gates the DMA transfer. Only one presync is
+	  allowed per request.
+	* Bit(21) is reserved.
+	* Bits(20:16) is the index of the semaphore to operate on.
+	* Bits(15:12) are reserved.
+	* Bits(11:0) are the semaphore value to use in operations.
+
+Overall, a request is processed in 4 steps:
+
+1. If specified, the presync semaphore condition must be true
+2. If enabled, the DMA transfer occurs
+3. If specified, the postsync semaphore conditions must be true
+4. If enabled, the doorbell is written
+
+By using the semaphores in conjunction with the workload running on the NSPs,
+the data pipeline can be synchronized such that the host can queue multiple
+requests of data for the workload to process, but the DMA Bridge will only copy
+the data into the memory of the workload when the workload is ready to process
+the next input.
+
+Response FIFO
+-------------
+
+Once a request is fully processed, a response FIFO element is generated if
+specified in pcie_dma_cmd. The structure of a response FIFO element:
+
+.. code-block:: c
+
+  struct response_elem {
+	u16 req_id;
+	u16 completion_code;
+  };
+
+req_id
+	matches the req_id of the request that generated this element.
+
+completion_code
+	status of this request. 0 is success. Non-zero is an error.
+
+The DMA Bridge will generate a MSI to the host as a reaction to activity in the
+response FIFO of a DBC. The DMA Bridge hardware has an IRQ storm mitigation
+algorithm, where it will only generate a MSI when the response FIFO transitions
+from empty to non-empty (unless force MSI is enabled and triggered). In
+response to this MSI, the host is expected to drain the response FIFO, and must
+take care to handle any race conditions between draining the FIFO, and the
+device inserting elements into the FIFO.
+
+Neural Network Control (NNC) Protocol
+=====================================
+
+The NNC protocol is how the host makes requests to the QSM to manage workloads.
+It uses the QAIC_CONTROL MHI channel.
+
+Each NNC request is packaged into a message. Each message is a series of
+transactions. A passthrough type transaction can contain elements known as
+commands.
+
+QSM requires NNC messages be little endian encoded and the fields be naturally
+aligned. Since there are 64-bit elements in some NNC messages, 64-bit alignment
+must be maintained.
+
+A message contains a header and then a series of transactions. A message may be
+at most 4K in size from QSM to the host. From the host to the QSM, a message
+can be at most 64K (maximum size of a single MHI packet), but there is a
+continuation feature where message N+1 can be marked as a continuation of
+message N. This is used for exceedingly large DMA xfer transactions.
+
+Transaction descriptions
+------------------------
+
+passthrough
+	Allows userspace to send an opaque payload directly to the QSM.
+	This is used for NNC commands. Userspace is responsible for managing
+	the QSM message requirements in the payload.
+
+dma_xfer
+	DMA transfer. Describes an object that the QSM should DMA into the
+	device via address and size tuples.
+
+activate
+	Activate a workload onto NSPs. The host must provide memory to be
+	used by the DBC.
+
+deactivate
+	Deactivate an active workload and return the NSPs to idle.
+
+status
+	Query the QSM about it's NNC implementation. Returns the NNC version,
+	and if CRC is used.
+
+terminate
+	Release a user's resources.
+
+dma_xfer_cont
+	Continuation of a previous DMA transfer. If a DMA transfer
+	cannot be specified in a single message (highly fragmented), this
+	transaction can be used to specify more ranges.
+
+validate_partition
+	Query to QSM to determine if a partition identifier is valid.
+
+Each message is tagged with a user id, and a partition id. The user id allows
+QSM to track resources, and release them when the user goes away (eg the process
+crashes). A partition id identifies the resource partition that QSM manages,
+which this message applies to.
+
+Messages may have CRCs. Messages should have CRCs applied until the QSM
+reports via the status transaction that CRCs are not needed. The QSM on the
+SA9000P requires CRCs for black channel safing.
+
+Subsystem Restart (SSR)
+=======================
+
+SSR is the concept of limiting the impact of an error. An AIC100 device may
+have multiple users, each with their own workload running. If the workload of
+one user crashes, the fallout of that should be limited to that workload and not
+impact other workloads. SSR accomplishes this.
+
+If a particular workload crashes, QSM notifies the host via the QAIC_SSR MHI
+channel. This notification identifies the workload by it's assigned DBC. A
+multi-stage recovery process is then used to cleanup both sides, and get the
+DBC/NSPs into a working state.
+
+When SSR occurs, any state in the workload is lost. Any inputs that were in
+process, or queued by not yet serviced, are lost. The loaded artifacts will
+remain in on-card DDR, but the host will need to re-activate the workload if
+it desires to recover the workload.
+
+Reliability, Accessibility, Serviceability (RAS)
+================================================
+
+AIC100 is expected to be deployed in server systems where RAS ideology is
+applied. Simply put, RAS is the concept of detecting, classifying, and
+reporting errors. While PCIe has AER (Advanced Error Reporting) which factors
+into RAS, AER does not allow for a device to report details about internal
+errors. Therefore, AIC100 implements a custom RAS mechanism. When a RAS event
+occurs, QSM will report the event with appropriate details via the QAIC_STATUS
+MHI channel. A sysadmin may determine that a particular device needs
+additional service based on RAS reports.
+
+Telemetry
+=========
+
+QSM has the ability to report various physical attributes of the device, and in
+some cases, to allow the host to control them. Examples include thermal limits,
+thermal readings, and power readings. These items are communicated via the
+QAIC_TELEMETRY MHI channel.
diff --git a/Documentation/accel/qaic/index.rst b/Documentation/accel/qaic/index.rst
new file mode 100644
index 000000000000..ad19b88d1a66
--- /dev/null
+++ b/Documentation/accel/qaic/index.rst
@@ -0,0 +1,13 @@
+.. SPDX-License-Identifier: GPL-2.0-only
+
+=====================================
+ accel/qaic Qualcomm Cloud AI driver
+=====================================
+
+The accel/qaic driver supports the Qualcomm Cloud AI machine learning
+accelerator cards.
+
+.. toctree::
+
+   qaic
+   aic100
diff --git a/Documentation/accel/qaic/qaic.rst b/Documentation/accel/qaic/qaic.rst
new file mode 100644
index 000000000000..72a70ab6e3a8
--- /dev/null
+++ b/Documentation/accel/qaic/qaic.rst
@@ -0,0 +1,170 @@
+.. SPDX-License-Identifier: GPL-2.0-only
+
+=============
+ QAIC driver
+=============
+
+The QAIC driver is the Kernel Mode Driver (KMD) for the AIC100 family of AI
+accelerator products.
+
+Interrupts
+==========
+
+While the AIC100 DMA Bridge hardware implements an IRQ storm mitigation
+mechanism, it is still possible for an IRQ storm to occur. A storm can happen
+if the workload is particularly quick, and the host is responsive. If the host
+can drain the response FIFO as quickly as the device can insert elements into
+it, then the device will frequently transition the response FIFO from empty to
+non-empty and generate MSIs at a rate equivalent to the speed of the
+workload's ability to process inputs. The lprnet (license plate reader network)
+workload is known to trigger this condition, and can generate in excess of 100k
+MSIs per second. It has been observed that most systems cannot tolerate this
+for long, and will crash due to some form of watchdog due to the overhead of
+the interrupt controller interrupting the host CPU.
+
+To mitigate this issue, the QAIC driver implements specific IRQ handling. When
+QAIC receives an IRQ, it disables that line. This prevents the interrupt
+controller from interrupting the CPU. Then AIC drains the FIFO. Once the FIFO
+is drained, QAIC implements a "last chance" polling algorithm where QAIC will
+sleep for a time to see if the workload will generate more activity. The IRQ
+line remains disabled during this time. If no activity is detected, QAIC exits
+polling mode and reenables the IRQ line.
+
+This mitigation in QAIC is very effective. The same lprnet usecase that
+generates 100k IRQs per second (per /proc/interrupts) is reduced to roughly 64
+IRQs over 5 minutes while keeping the host system stable, and having the same
+workload throughput performance (within run to run noise variation).
+
+
+Neural Network Control (NNC) Protocol
+=====================================
+
+The implementation of NNC is split between the KMD (QAIC) and UMD. In general
+QAIC understands how to encode/decode NNC wire protocol, and elements of the
+protocol which require kernel space knowledge to process (for example, mapping
+host memory to device IOVAs). QAIC understands the structure of a message, and
+all of the transactions. QAIC does not understand commands (the payload of a
+passthrough transaction).
+
+QAIC handles and enforces the required little endianness and 64-bit alignment,
+to the degree that it can. Since QAIC does not know the contents of a
+passthrough transaction, it relies on the UMD to satisfy the requirements.
+
+The terminate transaction is of particular use to QAIC. QAIC is not aware of
+the resources that are loaded onto a device since the majority of that activity
+occurs within NNC commands. As a result, QAIC does not have the means to
+roll back userspace activity. To ensure that a userspace client's resources
+are fully released in the case of a process crash, or a bug, QAIC uses the
+terminate command to let QSM know when a user has gone away, and the resources
+can be released.
+
+QSM can report a version number of the NNC protocol it supports. This is in the
+form of a Major number and a Minor number.
+
+Major number updates indicate changes to the NNC protocol which impact the
+message format, or transactions (impacts QAIC).
+
+Minor number updates indicate changes to the NNC protocol which impact the
+commands (does not impact QAIC).
+
+uAPI
+====
+
+QAIC defines a number of driver specific IOCTLs as part of the userspace API.
+This section describes those APIs.
+
+DRM_IOCTL_QAIC_MANAGE
+  This IOCTL allows userspace to send a NNC request to the QSM. The call will
+  block until a response is received, or the request has timed out.
+
+DRM_IOCTL_QAIC_CREATE_BO
+  This IOCTL allows userspace to allocate a buffer object (BO) which can send
+  or receive data from a workload. The call will return a GEM handle that
+  represents the allocated buffer. The BO is not usable until it has been
+  sliced (see DRM_IOCTL_QAIC_ATTACH_SLICE_BO).
+
+DRM_IOCTL_QAIC_MMAP_BO
+  This IOCTL allows userspace to prepare an allocated BO to be mmap'd into the
+  userspace process.
+
+DRM_IOCTL_QAIC_ATTACH_SLICE_BO
+  This IOCTL allows userspace to slice a BO in preparation for sending the BO
+  to the device. Slicing is the operation of describing what portions of a BO
+  get sent where to a workload. This requires a set of DMA transfers for the
+  DMA Bridge, and as such, locks the BO to a specific DBC.
+
+DRM_IOCTL_QAIC_EXECUTE_BO
+  This IOCTL allows userspace to submit a set of sliced BOs to the device. The
+  call is non-blocking. Success only indicates that the BOs have been queued
+  to the device, but does not guarantee they have been executed.
+
+DRM_IOCTL_QAIC_PARTIAL_EXECUTE_BO
+  This IOCTL operates like DRM_IOCTL_QAIC_EXECUTE_BO, but it allows userspace
+  to shrink the BOs sent to the device for this specific call. If a BO
+  typically has N inputs, but only a subset of those is available, this IOCTL
+  allows userspace to indicate that only the first M bytes of the BO should be
+  sent to the device to minimize data transfer overhead. This IOCTL dynamically
+  recomputes the slicing, and therefore has some processing overhead before the
+  BOs can be queued to the device.
+
+DRM_IOCTL_QAIC_WAIT_BO
+  This IOCTL allows userspace to determine when a particular BO has been
+  processed by the device. The call will block until either the BO has been
+  processed and can be re-queued to the device, or a timeout occurs.
+
+DRM_IOCTL_QAIC_PERF_STATS_BO
+  This IOCTL allows userspace to collect performance statistics on the most
+  recent execution of a BO. This allows userspace to construct an end to end
+  timeline of the BO processing for a performance analysis.
+
+DRM_IOCTL_QAIC_PART_DEV
+  This IOCTL allows userspace to request a duplicate "shadow device". This extra
+  accelN device is associated with a specific partition of resources on the
+  AIC100 device and can be used for limiting a process to some subset of
+  resources.
+
+Userspace Client Isolation
+==========================
+
+AIC100 supports multiple clients. Multiple DBCs can be consumed by a single
+client, and multiple clients can each consume one or more DBCs. Workloads
+may contain sensitive information therefore only the client that owns the
+workload should be allowed to interface with the DBC.
+
+Clients are identified by the instance associated with their open(). A client
+may only use memory they allocate, and DBCs that are assigned to their
+workloads. Attempts to access resources assigned to other clients will be
+rejected.
+
+Module parameters
+=================
+
+QAIC supports the following module parameters:
+
+**datapath_polling (bool)**
+
+Configures QAIC to use a polling thread for datapath events instead of relying
+on the device interrupts. Useful for platforms with broken multiMSI. Must be
+set at QAIC driver initialization. Default is 0 (off).
+
+**mhi_timeout_ms (unsigned int)**
+
+Sets the timeout value for MHI operations in milliseconds (ms). Must be set
+at the time the driver detects a device. Default is 2000 (2 seconds).
+
+**control_resp_timeout_s (unsigned int)**
+
+Sets the timeout value for QSM responses to NNC messages in seconds (s). Must
+be set at the time the driver is sending a request to QSM. Default is 60 (one
+minute).
+
+**wait_exec_default_timeout_ms (unsigned int)**
+
+Sets the default timeout for the wait_exec ioctl in milliseconds (ms). Must be
+set prior to the waic_exec ioctl call. A value specified in the ioctl call
+overrides this for that call. Default is 5000 (5 seconds).
+
+**datapath_poll_interval_us (unsigned int)**
+
+Sets the polling interval in microseconds (us) when datapath polling is active.
+Takes effect at the next polling interval. Default is 100 (100 us).