11802d0beSThomas Gleixner/* SPDX-License-Identifier: GPL-2.0-only */ 29762f12dSDave Martin/* 39762f12dSDave Martin * vlock.S - simple voting lock implementation for ARM 49762f12dSDave Martin * 59762f12dSDave Martin * Created by: Dave Martin, 2012-08-16 69762f12dSDave Martin * Copyright: (C) 2012-2013 Linaro Limited 79762f12dSDave Martin * 89762f12dSDave Martin * This algorithm is described in more detail in 9*e318b36eSJonathan Corbet * Documentation/arch/arm/vlocks.rst. 109762f12dSDave Martin */ 119762f12dSDave Martin 129762f12dSDave Martin#include <linux/linkage.h> 139762f12dSDave Martin#include "vlock.h" 149762f12dSDave Martin 15a2faac39SNick Desaulniers.arch armv7-a 16a2faac39SNick Desaulniers 179762f12dSDave Martin/* Select different code if voting flags can fit in a single word. */ 189762f12dSDave Martin#if VLOCK_VOTING_SIZE > 4 199762f12dSDave Martin#define FEW(x...) 209762f12dSDave Martin#define MANY(x...) x 219762f12dSDave Martin#else 229762f12dSDave Martin#define FEW(x...) x 239762f12dSDave Martin#define MANY(x...) 249762f12dSDave Martin#endif 259762f12dSDave Martin 269762f12dSDave Martin@ voting lock for first-man coordination 279762f12dSDave Martin 289762f12dSDave Martin.macro voting_begin rbase:req, rcpu:req, rscratch:req 299762f12dSDave Martin mov \rscratch, #1 309762f12dSDave Martin strb \rscratch, [\rbase, \rcpu] 319762f12dSDave Martin dmb 329762f12dSDave Martin.endm 339762f12dSDave Martin 349762f12dSDave Martin.macro voting_end rbase:req, rcpu:req, rscratch:req 359762f12dSDave Martin dmb 369762f12dSDave Martin mov \rscratch, #0 379762f12dSDave Martin strb \rscratch, [\rbase, \rcpu] 3840a5c0b4SWill Deacon dsb st 399762f12dSDave Martin sev 409762f12dSDave Martin.endm 419762f12dSDave Martin 429762f12dSDave Martin/* 439762f12dSDave Martin * The vlock structure must reside in Strongly-Ordered or Device memory. 449762f12dSDave Martin * This implementation deliberately eliminates most of the barriers which 459762f12dSDave Martin * would be required for other memory types, and assumes that independent 469762f12dSDave Martin * writes to neighbouring locations within a cacheline do not interfere 479762f12dSDave Martin * with one another. 489762f12dSDave Martin */ 499762f12dSDave Martin 509762f12dSDave Martin@ r0: lock structure base 519762f12dSDave Martin@ r1: CPU ID (0-based index within cluster) 529762f12dSDave MartinENTRY(vlock_trylock) 539762f12dSDave Martin add r1, r1, #VLOCK_VOTING_OFFSET 549762f12dSDave Martin 559762f12dSDave Martin voting_begin r0, r1, r2 569762f12dSDave Martin 579762f12dSDave Martin ldrb r2, [r0, #VLOCK_OWNER_OFFSET] @ check whether lock is held 589762f12dSDave Martin cmp r2, #VLOCK_OWNER_NONE 599762f12dSDave Martin bne trylock_fail @ fail if so 609762f12dSDave Martin 619762f12dSDave Martin @ Control dependency implies strb not observable before previous ldrb. 629762f12dSDave Martin 639762f12dSDave Martin strb r1, [r0, #VLOCK_OWNER_OFFSET] @ submit my vote 649762f12dSDave Martin 659762f12dSDave Martin voting_end r0, r1, r2 @ implies DMB 669762f12dSDave Martin 679762f12dSDave Martin @ Wait for the current round of voting to finish: 689762f12dSDave Martin 699762f12dSDave Martin MANY( mov r3, #VLOCK_VOTING_OFFSET ) 709762f12dSDave Martin0: 719762f12dSDave Martin MANY( ldr r2, [r0, r3] ) 729762f12dSDave Martin FEW( ldr r2, [r0, #VLOCK_VOTING_OFFSET] ) 739762f12dSDave Martin cmp r2, #0 749762f12dSDave Martin wfene 759762f12dSDave Martin bne 0b 769762f12dSDave Martin MANY( add r3, r3, #4 ) 779762f12dSDave Martin MANY( cmp r3, #VLOCK_VOTING_OFFSET + VLOCK_VOTING_SIZE ) 789762f12dSDave Martin MANY( bne 0b ) 799762f12dSDave Martin 809762f12dSDave Martin @ Check who won: 819762f12dSDave Martin 829762f12dSDave Martin dmb 839762f12dSDave Martin ldrb r2, [r0, #VLOCK_OWNER_OFFSET] 849762f12dSDave Martin eor r0, r1, r2 @ zero if I won, else nonzero 859762f12dSDave Martin bx lr 869762f12dSDave Martin 879762f12dSDave Martintrylock_fail: 889762f12dSDave Martin voting_end r0, r1, r2 899762f12dSDave Martin mov r0, #1 @ nonzero indicates that I lost 909762f12dSDave Martin bx lr 919762f12dSDave MartinENDPROC(vlock_trylock) 929762f12dSDave Martin 939762f12dSDave Martin@ r0: lock structure base 949762f12dSDave MartinENTRY(vlock_unlock) 959762f12dSDave Martin dmb 969762f12dSDave Martin mov r1, #VLOCK_OWNER_NONE 979762f12dSDave Martin strb r1, [r0, #VLOCK_OWNER_OFFSET] 9840a5c0b4SWill Deacon dsb st 999762f12dSDave Martin sev 1009762f12dSDave Martin bx lr 1019762f12dSDave MartinENDPROC(vlock_unlock) 102