[v3,1/8] 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>
---
 Documentation/accel/index.rst       |   1 +
 Documentation/accel/qaic/aic100.rst | 501 ++++++++++++++++++++++++++++++++++++
 Documentation/accel/qaic/index.rst  |  13 +
 Documentation/accel/qaic/qaic.rst   | 169 ++++++++++++
 4 files changed, 684 insertions(+)
 create mode 100644 Documentation/accel/qaic/aic100.rst
 create mode 100644 Documentation/accel/qaic/index.rst
 create mode 100644 Documentation/accel/qaic/qaic.rst

Reviewed-by: Jacek Lawrynowicz <jacek.lawrynowicz@linux.intel.com>

On 06.03.2023 22:33, Jeffrey Hugo wrote:
> 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>
> ---
>  Documentation/accel/index.rst       |   1 +
>  Documentation/accel/qaic/aic100.rst | 501 ++++++++++++++++++++++++++++++++++++
>  Documentation/accel/qaic/index.rst  |  13 +
>  Documentation/accel/qaic/qaic.rst   | 169 ++++++++++++
>  4 files changed, 684 insertions(+)
>  create mode 100644 Documentation/accel/qaic/aic100.rst
>  create mode 100644 Documentation/accel/qaic/index.rst
>  create mode 100644 Documentation/accel/qaic/qaic.rst
> 
> diff --git a/Documentation/accel/index.rst b/Documentation/accel/index.rst
> index 2b43c9a..e94a016 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 0000000..7ed95bb
> --- /dev/null
> +++ b/Documentation/accel/qaic/aic100.rst
> @@ -0,0 +1,501 @@
> +.. 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.
> +
> +| QAIC_LOOPBACK
> +| Channels 0 & 1
> +| Valid for AMSS
> +| Any data sent to the device on this channel is sent back to the host.
> +
> +| QAIC_SAHARA
> +| Channels 2 & 3
> +| Valid for SBL
> +| Used by SBL to obtain the runtime firmware from the host.
> +
> +| QAIC_DIAG
> +| Channels 4 & 5
> +| Valid for AMSS
> +| Used to communicate with QSM via the Diag protocol.
> +
> +| QAIC_SSR
> +| Channels 6 & 7
> +| Valid for AMSS
> +| Used to notify the host of subsystem restart events, and to offload SSR crashdumps.
> +
> +| QAIC_QDSS
> +| Channels 8 & 9
> +| Valid for AMSS
> +| Used for the Qualcomm Debug Subsystem.
> +
> +| QAIC_CONTROL
> +| Channels 10 & 11
> +| Valid for AMSS
> +| Used for the Neural Network Control (NNC) protocol.  This is the primary channel between host and
> +  QSM for managing workloads.
> +
> +| QAIC_LOGGING
> +| Channels 12 & 13
> +| Valid for SBL
> +| Used by the SBL to send the bootlog to the host.
> +
> +| QAIC_STATUS
> +| Channels 14 & 15
> +| Valid for AMSS
> +| Used to notify the host of Reliability, Accessibility, Serviceability (RAS) events.
> +
> +| QAIC_TELEMETRY
> +| Channels 16 & 17
> +| Valid for AMSS
> +| Used to get/set power/thermal/etc attributes.
> +
> +| QAIC_DEBUG
> +| Channels 18 & 19
> +| Valid for AMSS
> +| Not used.
> +
> +| QAIC_TIMESYNC
> +| Channels 20 & 21
> +| Valid for 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:
> +
> +| {
> +|	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:
> +
> +| {
> +| 	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 0000000..ad19b88
> --- /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 0000000..0c227b4
> --- /dev/null
> +++ b/Documentation/accel/qaic/qaic.rst
> @@ -0,0 +1,169 @@
> +.. 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 (unsigned int)**
> +
> +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 (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 (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 (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).