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accel/qaic: Add documentation for AIC100 accelerator driver

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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
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Jeffrey Hugo 2023-03-27 09:54:50 -06:00 committed by Jacek Lawrynowicz
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:maxdepth: 1
introduction
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.. 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.

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.. 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

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.. 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).