1 .. SPDX-License-Identifier: GPL-2.0-only 1 .. SPDX-License-Identifier: GPL-2.0-only
2 2
3 ============= 3 =============
4 QAIC driver 4 QAIC driver
5 ============= 5 =============
6 6
7 The QAIC driver is the Kernel Mode Driver (KMD 7 The QAIC driver is the Kernel Mode Driver (KMD) for the AIC100 family of AI
8 accelerator products. 8 accelerator products.
9 9
10 Interrupts 10 Interrupts
11 ========== 11 ==========
12 12
13 IRQ Storm Mitigation 13 IRQ Storm Mitigation
14 -------------------- 14 --------------------
15 15
16 While the AIC100 DMA Bridge hardware implement 16 While the AIC100 DMA Bridge hardware implements an IRQ storm mitigation
17 mechanism, it is still possible for an IRQ sto 17 mechanism, it is still possible for an IRQ storm to occur. A storm can happen
18 if the workload is particularly quick, and the 18 if the workload is particularly quick, and the host is responsive. If the host
19 can drain the response FIFO as quickly as the 19 can drain the response FIFO as quickly as the device can insert elements into
20 it, then the device will frequently transition 20 it, then the device will frequently transition the response FIFO from empty to
21 non-empty and generate MSIs at a rate equivale 21 non-empty and generate MSIs at a rate equivalent to the speed of the
22 workload's ability to process inputs. The lprn 22 workload's ability to process inputs. The lprnet (license plate reader network)
23 workload is known to trigger this condition, a 23 workload is known to trigger this condition, and can generate in excess of 100k
24 MSIs per second. It has been observed that mos 24 MSIs per second. It has been observed that most systems cannot tolerate this
25 for long, and will crash due to some form of w 25 for long, and will crash due to some form of watchdog due to the overhead of
26 the interrupt controller interrupting the host 26 the interrupt controller interrupting the host CPU.
27 27
28 To mitigate this issue, the QAIC driver implem 28 To mitigate this issue, the QAIC driver implements specific IRQ handling. When
29 QAIC receives an IRQ, it disables that line. T 29 QAIC receives an IRQ, it disables that line. This prevents the interrupt
30 controller from interrupting the CPU. Then AIC 30 controller from interrupting the CPU. Then AIC drains the FIFO. Once the FIFO
31 is drained, QAIC implements a "last chance" po 31 is drained, QAIC implements a "last chance" polling algorithm where QAIC will
32 sleep for a time to see if the workload will g 32 sleep for a time to see if the workload will generate more activity. The IRQ
33 line remains disabled during this time. If no 33 line remains disabled during this time. If no activity is detected, QAIC exits
34 polling mode and reenables the IRQ line. 34 polling mode and reenables the IRQ line.
35 35
36 This mitigation in QAIC is very effective. The 36 This mitigation in QAIC is very effective. The same lprnet usecase that
37 generates 100k IRQs per second (per /proc/inte 37 generates 100k IRQs per second (per /proc/interrupts) is reduced to roughly 64
38 IRQs over 5 minutes while keeping the host sys 38 IRQs over 5 minutes while keeping the host system stable, and having the same
39 workload throughput performance (within run to 39 workload throughput performance (within run to run noise variation).
40 40
41 Single MSI Mode 41 Single MSI Mode
42 --------------- 42 ---------------
43 43
44 MultiMSI is not well supported on all systems; 44 MultiMSI is not well supported on all systems; virtualized ones even less so
45 (circa 2023). Between hypervisors masking the 45 (circa 2023). Between hypervisors masking the PCIe MSI capability structure to
46 large memory requirements for vIOMMUs (require 46 large memory requirements for vIOMMUs (required for supporting MultiMSI), it is
47 useful to be able to fall back to a single MSI 47 useful to be able to fall back to a single MSI when needed.
48 48
49 To support this fallback, we allow the case wh 49 To support this fallback, we allow the case where only one MSI is able to be
50 allocated, and share that one MSI between MHI 50 allocated, and share that one MSI between MHI and the DBCs. The device detects
51 when only one MSI has been configured and dire 51 when only one MSI has been configured and directs the interrupts for the DBCs
52 to the interrupt normally used for MHI. Unfort 52 to the interrupt normally used for MHI. Unfortunately this means that the
53 interrupt handlers for every DBC and MHI wake 53 interrupt handlers for every DBC and MHI wake up for every interrupt that
54 arrives; however, the DBC threaded irq handler 54 arrives; however, the DBC threaded irq handlers only are started when work to be
55 done is detected (MHI will always start its th 55 done is detected (MHI will always start its threaded handler).
56 56
57 If the DBC is configured to force MSI interrup 57 If the DBC is configured to force MSI interrupts, this can circumvent the
58 software IRQ storm mitigation mentioned above. 58 software IRQ storm mitigation mentioned above. Since the MSI is shared it is
59 never disabled, allowing each new entry to the 59 never disabled, allowing each new entry to the FIFO to trigger a new interrupt.
60 60
61 61
62 Neural Network Control (NNC) Protocol 62 Neural Network Control (NNC) Protocol
63 ===================================== 63 =====================================
64 64
65 The implementation of NNC is split between the 65 The implementation of NNC is split between the KMD (QAIC) and UMD. In general
66 QAIC understands how to encode/decode NNC wire 66 QAIC understands how to encode/decode NNC wire protocol, and elements of the
67 protocol which require kernel space knowledge 67 protocol which require kernel space knowledge to process (for example, mapping
68 host memory to device IOVAs). QAIC understands 68 host memory to device IOVAs). QAIC understands the structure of a message, and
69 all of the transactions. QAIC does not underst 69 all of the transactions. QAIC does not understand commands (the payload of a
70 passthrough transaction). 70 passthrough transaction).
71 71
72 QAIC handles and enforces the required little 72 QAIC handles and enforces the required little endianness and 64-bit alignment,
73 to the degree that it can. Since QAIC does not 73 to the degree that it can. Since QAIC does not know the contents of a
74 passthrough transaction, it relies on the UMD 74 passthrough transaction, it relies on the UMD to satisfy the requirements.
75 75
76 The terminate transaction is of particular use 76 The terminate transaction is of particular use to QAIC. QAIC is not aware of
77 the resources that are loaded onto a device si 77 the resources that are loaded onto a device since the majority of that activity
78 occurs within NNC commands. As a result, QAIC 78 occurs within NNC commands. As a result, QAIC does not have the means to
79 roll back userspace activity. To ensure that a 79 roll back userspace activity. To ensure that a userspace client's resources
80 are fully released in the case of a process cr 80 are fully released in the case of a process crash, or a bug, QAIC uses the
81 terminate command to let QSM know when a user 81 terminate command to let QSM know when a user has gone away, and the resources
82 can be released. 82 can be released.
83 83
84 QSM can report a version number of the NNC pro 84 QSM can report a version number of the NNC protocol it supports. This is in the
85 form of a Major number and a Minor number. 85 form of a Major number and a Minor number.
86 86
87 Major number updates indicate changes to the N 87 Major number updates indicate changes to the NNC protocol which impact the
88 message format, or transactions (impacts QAIC) 88 message format, or transactions (impacts QAIC).
89 89
90 Minor number updates indicate changes to the N 90 Minor number updates indicate changes to the NNC protocol which impact the
91 commands (does not impact QAIC). 91 commands (does not impact QAIC).
92 92
93 uAPI 93 uAPI
94 ==== 94 ====
95 95
96 QAIC creates an accel device per physical PCIe 96 QAIC creates an accel device per physical PCIe device. This accel device exists
97 for as long as the PCIe device is known to Lin 97 for as long as the PCIe device is known to Linux.
98 98
99 The PCIe device may not be in the state to acc 99 The PCIe device may not be in the state to accept requests from userspace at
100 all times. QAIC will trigger KOBJ_ONLINE/OFFLI 100 all times. QAIC will trigger KOBJ_ONLINE/OFFLINE uevents to advertise when the
101 device can accept requests (ONLINE) and when t 101 device can accept requests (ONLINE) and when the device is no longer accepting
102 requests (OFFLINE) because of a reset or other 102 requests (OFFLINE) because of a reset or other state transition.
103 103
104 QAIC defines a number of driver specific IOCTL 104 QAIC defines a number of driver specific IOCTLs as part of the userspace API.
105 105
106 DRM_IOCTL_QAIC_MANAGE 106 DRM_IOCTL_QAIC_MANAGE
107 This IOCTL allows userspace to send a NNC re 107 This IOCTL allows userspace to send a NNC request to the QSM. The call will
108 block until a response is received, or the r 108 block until a response is received, or the request has timed out.
109 109
110 DRM_IOCTL_QAIC_CREATE_BO 110 DRM_IOCTL_QAIC_CREATE_BO
111 This IOCTL allows userspace to allocate a bu 111 This IOCTL allows userspace to allocate a buffer object (BO) which can send
112 or receive data from a workload. The call wi 112 or receive data from a workload. The call will return a GEM handle that
113 represents the allocated buffer. The BO is n 113 represents the allocated buffer. The BO is not usable until it has been
114 sliced (see DRM_IOCTL_QAIC_ATTACH_SLICE_BO). 114 sliced (see DRM_IOCTL_QAIC_ATTACH_SLICE_BO).
115 115
116 DRM_IOCTL_QAIC_MMAP_BO 116 DRM_IOCTL_QAIC_MMAP_BO
117 This IOCTL allows userspace to prepare an al 117 This IOCTL allows userspace to prepare an allocated BO to be mmap'd into the
118 userspace process. 118 userspace process.
119 119
120 DRM_IOCTL_QAIC_ATTACH_SLICE_BO 120 DRM_IOCTL_QAIC_ATTACH_SLICE_BO
121 This IOCTL allows userspace to slice a BO in 121 This IOCTL allows userspace to slice a BO in preparation for sending the BO
122 to the device. Slicing is the operation of d 122 to the device. Slicing is the operation of describing what portions of a BO
123 get sent where to a workload. This requires 123 get sent where to a workload. This requires a set of DMA transfers for the
124 DMA Bridge, and as such, locks the BO to a s 124 DMA Bridge, and as such, locks the BO to a specific DBC.
125 125
126 DRM_IOCTL_QAIC_EXECUTE_BO 126 DRM_IOCTL_QAIC_EXECUTE_BO
127 This IOCTL allows userspace to submit a set 127 This IOCTL allows userspace to submit a set of sliced BOs to the device. The
128 call is non-blocking. Success only indicates 128 call is non-blocking. Success only indicates that the BOs have been queued
129 to the device, but does not guarantee they h 129 to the device, but does not guarantee they have been executed.
130 130
131 DRM_IOCTL_QAIC_PARTIAL_EXECUTE_BO 131 DRM_IOCTL_QAIC_PARTIAL_EXECUTE_BO
132 This IOCTL operates like DRM_IOCTL_QAIC_EXEC 132 This IOCTL operates like DRM_IOCTL_QAIC_EXECUTE_BO, but it allows userspace
133 to shrink the BOs sent to the device for thi 133 to shrink the BOs sent to the device for this specific call. If a BO
134 typically has N inputs, but only a subset of 134 typically has N inputs, but only a subset of those is available, this IOCTL
135 allows userspace to indicate that only the f 135 allows userspace to indicate that only the first M bytes of the BO should be
136 sent to the device to minimize data transfer 136 sent to the device to minimize data transfer overhead. This IOCTL dynamically
137 recomputes the slicing, and therefore has so 137 recomputes the slicing, and therefore has some processing overhead before the
138 BOs can be queued to the device. 138 BOs can be queued to the device.
139 139
140 DRM_IOCTL_QAIC_WAIT_BO 140 DRM_IOCTL_QAIC_WAIT_BO
141 This IOCTL allows userspace to determine whe 141 This IOCTL allows userspace to determine when a particular BO has been
142 processed by the device. The call will block 142 processed by the device. The call will block until either the BO has been
143 processed and can be re-queued to the device 143 processed and can be re-queued to the device, or a timeout occurs.
144 144
145 DRM_IOCTL_QAIC_PERF_STATS_BO 145 DRM_IOCTL_QAIC_PERF_STATS_BO
146 This IOCTL allows userspace to collect perfo 146 This IOCTL allows userspace to collect performance statistics on the most
147 recent execution of a BO. This allows usersp 147 recent execution of a BO. This allows userspace to construct an end to end
148 timeline of the BO processing for a performa 148 timeline of the BO processing for a performance analysis.
149 149
150 DRM_IOCTL_QAIC_DETACH_SLICE_BO 150 DRM_IOCTL_QAIC_DETACH_SLICE_BO
151 This IOCTL allows userspace to remove the sl 151 This IOCTL allows userspace to remove the slicing information from a BO that
152 was originally provided by a call to DRM_IOC 152 was originally provided by a call to DRM_IOCTL_QAIC_ATTACH_SLICE_BO. This
153 is the inverse of DRM_IOCTL_QAIC_ATTACH_SLIC 153 is the inverse of DRM_IOCTL_QAIC_ATTACH_SLICE_BO. The BO must be idle for
154 DRM_IOCTL_QAIC_DETACH_SLICE_BO to be called. 154 DRM_IOCTL_QAIC_DETACH_SLICE_BO to be called. After a successful detach slice
155 operation the BO may have new slicing inform 155 operation the BO may have new slicing information attached with a new call
156 to DRM_IOCTL_QAIC_ATTACH_SLICE_BO. After det 156 to DRM_IOCTL_QAIC_ATTACH_SLICE_BO. After detach slice, the BO cannot be
157 executed until after a new attach slice oper 157 executed until after a new attach slice operation. Combining attach slice
158 and detach slice calls allows userspace to u 158 and detach slice calls allows userspace to use a BO with multiple workloads.
159 159
160 Userspace Client Isolation 160 Userspace Client Isolation
161 ========================== 161 ==========================
162 162
163 AIC100 supports multiple clients. Multiple DBC 163 AIC100 supports multiple clients. Multiple DBCs can be consumed by a single
164 client, and multiple clients can each consume 164 client, and multiple clients can each consume one or more DBCs. Workloads
165 may contain sensitive information therefore on 165 may contain sensitive information therefore only the client that owns the
166 workload should be allowed to interface with t 166 workload should be allowed to interface with the DBC.
167 167
168 Clients are identified by the instance associa 168 Clients are identified by the instance associated with their open(). A client
169 may only use memory they allocate, and DBCs th 169 may only use memory they allocate, and DBCs that are assigned to their
170 workloads. Attempts to access resources assign 170 workloads. Attempts to access resources assigned to other clients will be
171 rejected. 171 rejected.
172 172
173 Module parameters 173 Module parameters
174 ================= 174 =================
175 175
176 QAIC supports the following module parameters: 176 QAIC supports the following module parameters:
177 177
178 **datapath_polling (bool)** 178 **datapath_polling (bool)**
179 179
180 Configures QAIC to use a polling thread for da 180 Configures QAIC to use a polling thread for datapath events instead of relying
181 on the device interrupts. Useful for platforms 181 on the device interrupts. Useful for platforms with broken multiMSI. Must be
182 set at QAIC driver initialization. Default is 182 set at QAIC driver initialization. Default is 0 (off).
183 183
184 **mhi_timeout_ms (unsigned int)** 184 **mhi_timeout_ms (unsigned int)**
185 185
186 Sets the timeout value for MHI operations in m 186 Sets the timeout value for MHI operations in milliseconds (ms). Must be set
187 at the time the driver detects a device. Defau 187 at the time the driver detects a device. Default is 2000 (2 seconds).
188 188
189 **control_resp_timeout_s (unsigned int)** 189 **control_resp_timeout_s (unsigned int)**
190 190
191 Sets the timeout value for QSM responses to NN 191 Sets the timeout value for QSM responses to NNC messages in seconds (s). Must
192 be set at the time the driver is sending a req 192 be set at the time the driver is sending a request to QSM. Default is 60 (one
193 minute). 193 minute).
194 194
195 **wait_exec_default_timeout_ms (unsigned int)* 195 **wait_exec_default_timeout_ms (unsigned int)**
196 196
197 Sets the default timeout for the wait_exec ioc 197 Sets the default timeout for the wait_exec ioctl in milliseconds (ms). Must be
198 set prior to the waic_exec ioctl call. A value 198 set prior to the waic_exec ioctl call. A value specified in the ioctl call
199 overrides this for that call. Default is 5000 199 overrides this for that call. Default is 5000 (5 seconds).
200 200
201 **datapath_poll_interval_us (unsigned int)** 201 **datapath_poll_interval_us (unsigned int)**
202 202
203 Sets the polling interval in microseconds (us) 203 Sets the polling interval in microseconds (us) when datapath polling is active.
204 Takes effect at the next polling interval. Def 204 Takes effect at the next polling interval. Default is 100 (100 us).
205 205
206 **timesync_delay_ms (unsigned int)** 206 **timesync_delay_ms (unsigned int)**
207 207
208 Sets the time interval in milliseconds (ms) be 208 Sets the time interval in milliseconds (ms) between two consecutive timesync
209 operations. Default is 1000 (1000 ms). 209 operations. Default is 1000 (1000 ms).
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