Add documentation covering both the QAIC driver, and the device that it
drives.
Change-Id: Iee519cc0a276249c4e8684507d27ae2c33e29aeb
Signed-off-by: Jeffrey Hugo <quic_jhugo@xxxxxxxxxxx>
---
Documentation/gpu/drivers.rst | 1 +
Documentation/gpu/qaic.rst | 567 ++++++++++++++++++++++++++++++++++++++++++
2 files changed, 568 insertions(+)
create mode 100644 Documentation/gpu/qaic.rst
diff --git a/Documentation/gpu/drivers.rst b/Documentation/gpu/drivers.rst
index 3a52f48..433dac5 100644
--- a/Documentation/gpu/drivers.rst
+++ b/Documentation/gpu/drivers.rst
@@ -18,6 +18,7 @@ GPU Driver Documentation
xen-front
afbc
komeda-kms
+ qaic
.. only:: subproject and html
diff --git a/Documentation/gpu/qaic.rst b/Documentation/gpu/qaic.rst
new file mode 100644
index 0000000..3414f98
--- /dev/null
+++ b/Documentation/gpu/qaic.rst
@@ -0,0 +1,567 @@
+Overview
+--------
+QAIC is the driver for the Qualcomm Cloud AI 100/AIC100 and SA9000P (part of
+Snapdragon Ride) products. Qualcomm Cloud AI 100 is a PCIe adapter card which
+contains a dedicated SoC ASIC for the purpose of efficiently running Artificial
+Intelligence (AI) Deep Learning inference workloads.
+
+The PCIe interface of Qualcomm Cloud AI 100 is capable of Gen4 x8. An
+individual SoC on a card can have up to 16 NSPs for running workloads. Each SoC
+has a A53 management CPU. On card, there can be up to 32 GB of DDR
+
+Multiple Qualcomm Cloud AI 100 cards can be hosted in a single system to scale
+overall performance.
+
+
+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)/
+ProductID(PID) combination to uniquely identify itself to the host. AIC100
+uses the standard Qualcomm VID (0x17cb). All AIC100 instances use the same
+AIC100 PID (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-
+QSM (QAIC Service Manager)
+NSPs (Neural Signal Processor)
+DMA Bridge
+DDR
+MHI (Modem Host Interface)
+
+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 (QAIC/userspace) 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.
+
+MHI - AIC100 has one MHI interface over PCIe. MHI itself is documented at
+Documentation/mhi/index.rst MHI is the mechanism the host (QAIC/userspace)
+uses to communicate with the QSM. Except for workload data via the DMA Bridge,
+all interaction with the device occurs via MHI.
+
+
+High-level Use Flow
+-------------------
+AIC100 is a programmable accelerator. AIC100 is 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 utilitized
+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 synchonizes 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.
+
+
+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, Accessability, 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
+----------
+The DMA Bridge is one of the main interfaces to the host (QAIC) 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 to 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 to 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
+0x1000 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 contigious 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.
+
+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.
+
+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.
+
+It is still possible for an IRQ storm to occur, 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 equilivelent 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 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. QAIC understands the structure of a message, and all of the
+transactions. QAIC does not understand commands (the payload of a passthrough
+transaction).
+
+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. QAIC ensures the data is mapped to
+ device accessible addresses.
+
+activate- Activate a workload onto NSPs. QAIC uses this transaction to assign
+ host memory to be used by the DBC. QAIC uses the response which
+ contains the assigned DBC to ensure only the requesting user is allowed
+ to access the assigned DBC.
+
+deactivate- Deactivate an active workload and return the NSPs to idle. QAIC
+ uses the transaction to remove access to a DBC from the requesting user.
+
+status- Query the QSM about it's NNC implementation. Returns the NNC version,
+ and if CRC is used.
+
+terminate- Release a user's resources. Used by QAIC to indicate to QSM that a
+ particular user has gone away, and all of their resources can be cleaned
+ up.
+
+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. At each stage, QAIC sends uevents on the DBC to
+userspace so that userspace is aware of the SSR event, and the event's progress.
+
+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 userspace will need to re-activate the workload if
+it desires to recover the workload.
+
+
+Reliability, Accessability, 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. QAIC will receive these reports, decode them, and print the event
+to the kernel log (much like AER handling). 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
+
+Many of these attributes apply to multiple components of the device. The
+scheme QAIC uses is that attribute0 refers to that attribute at the board level.
+Attribute1 refers to that attribute at the SoC level. Attribute2 refers to that
+attribute at the DDR level.
+
+
+Versioning
+----------
+QAIC provides a module/DRM version of the scheme Major.Minor.Patch
+
+The Major number is incremented when a code change results in a breaking change
+to the uAPI. This should never happen.
+
+The Minor number is incremented when a code change results in a backwards
+compatible extension (new feature) to the uAPI. This is expected to be rare.
+
+The Patch number is incremented when a code change results in an internal change
+to QAIC, such as a bug fix. This can be used to determine if the current
+version of the driver contains some known update.
+
+An update to the Major number will reset the Minor number and Patch number.
+An update to the Minor number will reset the Patch number. Examples:
+1.2.3 -> 2.0.0
+1.2.3 -> 1.3.0
+
+Versions:
+1.0.X - initial version of the DRM driver, accepted into upstream Linux
+
+
+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 th
+ 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.
--
2.7.4
