1/* 2 * Copyright (c) 2014 Wind River Systems, Inc. 3 * 4 * SPDX-License-Identifier: Apache-2.0 5 */ 6 7/** 8 * @file 9 * @brief Handling of transitions to-and-from regular IRQs (RIRQ) 10 * 11 * This module implements the code for handling entry to and exit from regular 12 * IRQs. 13 * 14 * See isr_wrapper.S for details. 15 */ 16 17#include <zephyr/kernel_structs.h> 18#include <offsets_short.h> 19#include <zephyr/toolchain.h> 20#include <zephyr/linker/sections.h> 21#include <zephyr/arch/cpu.h> 22#include <swap_macros.h> 23#include <zephyr/arch/arc/asm-compat/assembler.h> 24 25GTEXT(_rirq_enter) 26GTEXT(_rirq_exit) 27GTEXT(_rirq_newthread_switch) 28 29/* 30 31=========================================================== 32 RETURN FROM INTERRUPT TO COOPERATIVE THREAD 33=========================================================== 34 35That's a special case because: 36 1. We return from IRQ handler to a cooperative thread 37 2. During IRQ handling context switch did happen 38 3. Returning to a thread which previously gave control 39 to another thread because of: 40 - Calling k_sleep() 41 - Explicitly yielding 42 - Bumping into locked sync primitive etc 43 44What (3) means is before passing control to another thread our thread 45in question: 46 a. Stashed all precious caller-saved registers on its stack 47 b. Pushed return address to the top of the stack as well 48 49That's how thread's stack looks like right before jumping to another thread: 50----------------------------->8--------------------------------- 51PRE-CONTEXT-SWITCH STACK 52 53 lower_addr, let's say: 0x1000 54 55 -------------------------------------- 56 SP -> | Return address; PC (Program Counter), in fact value taken from 57 | BLINK register in arch_switch() 58 -------------------------------------- 59 | STATUS32 value, we explicitly save it here for later usage, read-on 60 -------------------------------------- 61 | Caller-saved registers: some of R0-R12 62 -------------------------------------- 63 |... 64 |... 65 66 higher_addr, let's say: 0x2000 67----------------------------->8--------------------------------- 68 69When context gets switched the kernel saves callee-saved registers in the 70thread's stack right on top of pre-switch contents so that's what we have: 71----------------------------->8--------------------------------- 72POST-CONTEXT-SWITCH STACK 73 74 lower_addr, let's say: 0x1000 75 76 -------------------------------------- 77SP -> | Callee-saved registers: see struct _callee_saved_stack{} 78 | |- R13 79 | |- R14 80 | | ... 81 | \- FP 82 | ... 83 -------------------------------------- 84 | Return address; PC (Program Counter) 85 -------------------------------------- 86 | STATUS32 value 87 -------------------------------------- 88 | Caller-saved registers: some of R0-R12 89 -------------------------------------- 90 |... 91 |... 92 93 higher_addr, let's say: 0x2000 94----------------------------->8--------------------------------- 95 96So how do we return in such a complex scenario. 97 98First we restore callee-saved regs with help of _load_callee_saved_regs(). 99Now we're back to PRE-CONTEXT-SWITCH STACK (see above). 100 101Logically our next step is to load return address from the top of the stack 102and jump to that address to continue execution of the desired thread, but 103we're still in interrupt handling mode and the only way to return to normal 104execution mode is to execute "rtie" instruction. And here we need to deal 105with peculiarities of return from IRQ on ARCv2 cores. 106 107Instead of simple jump to a return address stored in the tip of thread's stack 108(with subsequent interrupt enable) ARCv2 core additionally automatically 109restores some registers from stack. Most important ones are 110PC ("Program Counter") which holds address of the next instruction to execute 111and STATUS32 which holds imortant flags including global interrupt enable, 112zero, carry etc. 113 114To make things worse depending on ARC core configuration and run-time setup 115of certain features different set of registers will be restored. 116 117Typically those same registers are automatically saved on stack on entry to 118an interrupt, but remember we're returning to the thread which was 119not interrupted by interrupt and so on its stack there're no automatically 120saved registers, still inevitably on RTIE execution register restoration 121will happen. So if we do nothing special we'll end-up with that: 122----------------------------->8--------------------------------- 123 lower_addr, let's say: 0x1000 124 125 -------------------------------------- 126 # | Return address; PC (Program Counter) 127 | -------------------------------------- 128 | | STATUS32 value 129 | -------------------------------------- 130 | 131 sizeof(_irq_stack_frame) 132 | 133 | | Caller-saved registers: R0-R12 134 V -------------------------------------- 135 |... 136 SP -> | < Some data on thread's stack> 137 |... 138 139 higher_addr, let's say: 0x2000 140----------------------------->8--------------------------------- 141 142I.e. we'll go much deeper down the stack over needed return address, read 143some value from unexpected location in stack and will try to jump there. 144Nobody knows were we end-up then. 145 146To work-around that problem we need to mimic existance of IRQ stack frame 147of which we really only need return address obviously to return where we 148need to. For that we just shift SP so that it points sizeof(_irq_stack_frame) 149above like that: 150----------------------------->8--------------------------------- 151 lower_addr, let's say: 0x1000 152 153 SP -> | 154 A | < Some unrelated data > 155 | | 156 | 157 sizeof(_irq_stack_frame) 158 | 159 | -------------------------------------- 160 | | Return address; PC (Program Counter) 161 | -------------------------------------- 162 # | STATUS32 value 163 -------------------------------------- 164 | Caller-saved registers: R0-R12 165 -------------------------------------- 166 |... 167 | < Some data on thread's stack> 168 |... 169 170 higher_addr, let's say: 0x2000 171----------------------------->8--------------------------------- 172 173Indeed R0-R13 "restored" from IRQ stack frame will contain garbage but 174it makes no difference because we're returning to execution of code as if 175we're returning from yet another function call and so we will restore 176all needed registers from the stack. 177 178One other important remark here is R13. 179 180CPU hardware automatically save/restore registers in pairs and since we 181wanted to save/restore R12 in IRQ stack frame as a caller-saved register we 182just happen to do that for R13 as well. But given compiler treats it as 183a callee-saved register we save/restore it separately in _callee_saved_stack 184structure. And when we restore callee-saved registers from stack we among 185other registers recover R13. But later on return from IRQ with RTIE 186instruction, R13 will be "restored" again from fake IRQ stack frame and 187if we don't copy correct R13 value to fake IRQ stack frame R13 value 188will be corrupted. 189 190*/ 191 192/** 193 * @brief Work to be done before handing control to an IRQ ISR 194 * 195 * The processor pushes automatically all registers that need to be saved. 196 * However, since the processor always runs at kernel privilege there is no 197 * automatic switch to the IRQ stack: this must be done in software. 198 * 199 * Assumption by _isr_demux: r3 is untouched by _rirq_enter. 200 */ 201 202SECTION_FUNC(TEXT, _rirq_enter) 203 204/* the ISR will be handled in separate interrupt stack, 205 * so stack checking must be diabled, or exception will 206 * be caused 207 */ 208 _disable_stack_checking r2 209 clri 210 211 /* check whether irq stack is used, if 212 * not switch to isr stack 213 */ 214 _check_and_inc_int_nest_counter r0, r1 215 216 bne.d rirq_nest 217 MOVR r0, sp 218 219 _get_curr_cpu_irq_stack sp 220rirq_nest: 221 PUSHR r0 222 223 seti 224 j _isr_demux 225 226 227/** 228 * @brief Work to be done exiting an IRQ 229 */ 230 231SECTION_FUNC(TEXT, _rirq_exit) 232 clri 233 234 POPR sp 235 236 _dec_int_nest_counter r0, r1 237 238 _check_nest_int_by_irq_act r0, r1 239 240 jne _rirq_no_switch 241 242 /* sp is struct k_thread **old of z_arc_switch_in_isr which is a wrapper of 243 * z_get_next_switch_handle. r0 contains the 1st thread in ready queue. If it isn't NULL, 244 * then do switch to this thread. 245 */ 246 _get_next_switch_handle 247 248 CMPR r0, 0 249 beq _rirq_no_switch 250 251#ifdef CONFIG_ARC_SECURE_FIRMWARE 252 /* here need to remember SEC_STAT.IRM bit */ 253 lr r3, [_ARC_V2_SEC_STAT] 254 push_s r3 255#endif 256 257 /* r2 is old thread 258 * _thread_arch.relinquish_cause is 32 bit despite of platform bittnes 259 */ 260 _st32_huge_offset _CAUSE_RIRQ, r2, _thread_offset_to_relinquish_cause, r1 261 262 _irq_store_old_thread_callee_regs 263 264 /* mov new thread (r0) to r2 */ 265 MOVR r2, r0 266 267/* _rirq_newthread_switch required by exception handling */ 268.align 4 269_rirq_newthread_switch: 270 271 _load_new_thread_callee_regs 272 273 breq r3, _CAUSE_RIRQ, _rirq_switch_from_rirq 274 nop_s 275 breq r3, _CAUSE_FIRQ, _rirq_switch_from_firq 276 nop_s 277 278 /* fall through */ 279 280.align 4 281_rirq_switch_from_coop: 282 283 /* for a cooperative switch, it's not in irq, so 284 * need to set some regs for irq return 285 */ 286 _set_misc_regs_irq_switch_from_coop 287 288 /* 289 * See verbose explanation of 290 * RETURN FROM INTERRUPT TO COOPERATIVE THREAD above 291 */ 292 293 /* carve fake stack */ 294 SUBR sp, sp, ___isf_t_pc_OFFSET 295 296 297#ifdef CONFIG_ARC_HAS_ZOL 298 /* reset zero-overhead loops */ 299 STR 0, sp, ___isf_t_lp_end_OFFSET 300#endif /* CONFIG_ARC_HAS_ZOL */ 301 302 /* 303 * r13 is part of both the callee and caller-saved register sets because 304 * the processor is only able to save registers in pair in the regular 305 * IRQ prologue. r13 thus has to be set to its correct value in the IRQ 306 * stack frame. 307 */ 308 STR r13, sp, ___isf_t_r13_OFFSET 309 310#ifdef CONFIG_INSTRUMENT_THREAD_SWITCHING 311 PUSHR blink 312 313 bl z_thread_mark_switched_in 314 315 POPR blink 316#endif 317 /* stack now has the IRQ stack frame layout, pointing to sp */ 318 /* rtie will pop the rest from the stack */ 319 rtie 320 321.align 4 322_rirq_switch_from_firq: 323_rirq_switch_from_rirq: 324 325 _set_misc_regs_irq_switch_from_irq 326 327#ifdef CONFIG_INSTRUMENT_THREAD_SWITCHING 328 PUSHR blink 329 330 bl z_thread_mark_switched_in 331 332 POPR blink 333#endif 334_rirq_no_switch: 335 rtie 336
