162306a36Sopenharmony_ci/* SPDX-License-Identifier: GPL-2.0-only */ 262306a36Sopenharmony_ci/* 362306a36Sopenharmony_ci * vlock.S - simple voting lock implementation for ARM 462306a36Sopenharmony_ci * 562306a36Sopenharmony_ci * Created by: Dave Martin, 2012-08-16 662306a36Sopenharmony_ci * Copyright: (C) 2012-2013 Linaro Limited 762306a36Sopenharmony_ci * 862306a36Sopenharmony_ci * This algorithm is described in more detail in 962306a36Sopenharmony_ci * Documentation/arch/arm/vlocks.rst. 1062306a36Sopenharmony_ci */ 1162306a36Sopenharmony_ci 1262306a36Sopenharmony_ci#include <linux/linkage.h> 1362306a36Sopenharmony_ci#include "vlock.h" 1462306a36Sopenharmony_ci 1562306a36Sopenharmony_ci.arch armv7-a 1662306a36Sopenharmony_ci 1762306a36Sopenharmony_ci/* Select different code if voting flags can fit in a single word. */ 1862306a36Sopenharmony_ci#if VLOCK_VOTING_SIZE > 4 1962306a36Sopenharmony_ci#define FEW(x...) 2062306a36Sopenharmony_ci#define MANY(x...) x 2162306a36Sopenharmony_ci#else 2262306a36Sopenharmony_ci#define FEW(x...) x 2362306a36Sopenharmony_ci#define MANY(x...) 2462306a36Sopenharmony_ci#endif 2562306a36Sopenharmony_ci 2662306a36Sopenharmony_ci@ voting lock for first-man coordination 2762306a36Sopenharmony_ci 2862306a36Sopenharmony_ci.macro voting_begin rbase:req, rcpu:req, rscratch:req 2962306a36Sopenharmony_ci mov \rscratch, #1 3062306a36Sopenharmony_ci strb \rscratch, [\rbase, \rcpu] 3162306a36Sopenharmony_ci dmb 3262306a36Sopenharmony_ci.endm 3362306a36Sopenharmony_ci 3462306a36Sopenharmony_ci.macro voting_end rbase:req, rcpu:req, rscratch:req 3562306a36Sopenharmony_ci dmb 3662306a36Sopenharmony_ci mov \rscratch, #0 3762306a36Sopenharmony_ci strb \rscratch, [\rbase, \rcpu] 3862306a36Sopenharmony_ci dsb st 3962306a36Sopenharmony_ci sev 4062306a36Sopenharmony_ci.endm 4162306a36Sopenharmony_ci 4262306a36Sopenharmony_ci/* 4362306a36Sopenharmony_ci * The vlock structure must reside in Strongly-Ordered or Device memory. 4462306a36Sopenharmony_ci * This implementation deliberately eliminates most of the barriers which 4562306a36Sopenharmony_ci * would be required for other memory types, and assumes that independent 4662306a36Sopenharmony_ci * writes to neighbouring locations within a cacheline do not interfere 4762306a36Sopenharmony_ci * with one another. 4862306a36Sopenharmony_ci */ 4962306a36Sopenharmony_ci 5062306a36Sopenharmony_ci@ r0: lock structure base 5162306a36Sopenharmony_ci@ r1: CPU ID (0-based index within cluster) 5262306a36Sopenharmony_ciENTRY(vlock_trylock) 5362306a36Sopenharmony_ci add r1, r1, #VLOCK_VOTING_OFFSET 5462306a36Sopenharmony_ci 5562306a36Sopenharmony_ci voting_begin r0, r1, r2 5662306a36Sopenharmony_ci 5762306a36Sopenharmony_ci ldrb r2, [r0, #VLOCK_OWNER_OFFSET] @ check whether lock is held 5862306a36Sopenharmony_ci cmp r2, #VLOCK_OWNER_NONE 5962306a36Sopenharmony_ci bne trylock_fail @ fail if so 6062306a36Sopenharmony_ci 6162306a36Sopenharmony_ci @ Control dependency implies strb not observable before previous ldrb. 6262306a36Sopenharmony_ci 6362306a36Sopenharmony_ci strb r1, [r0, #VLOCK_OWNER_OFFSET] @ submit my vote 6462306a36Sopenharmony_ci 6562306a36Sopenharmony_ci voting_end r0, r1, r2 @ implies DMB 6662306a36Sopenharmony_ci 6762306a36Sopenharmony_ci @ Wait for the current round of voting to finish: 6862306a36Sopenharmony_ci 6962306a36Sopenharmony_ci MANY( mov r3, #VLOCK_VOTING_OFFSET ) 7062306a36Sopenharmony_ci0: 7162306a36Sopenharmony_ci MANY( ldr r2, [r0, r3] ) 7262306a36Sopenharmony_ci FEW( ldr r2, [r0, #VLOCK_VOTING_OFFSET] ) 7362306a36Sopenharmony_ci cmp r2, #0 7462306a36Sopenharmony_ci wfene 7562306a36Sopenharmony_ci bne 0b 7662306a36Sopenharmony_ci MANY( add r3, r3, #4 ) 7762306a36Sopenharmony_ci MANY( cmp r3, #VLOCK_VOTING_OFFSET + VLOCK_VOTING_SIZE ) 7862306a36Sopenharmony_ci MANY( bne 0b ) 7962306a36Sopenharmony_ci 8062306a36Sopenharmony_ci @ Check who won: 8162306a36Sopenharmony_ci 8262306a36Sopenharmony_ci dmb 8362306a36Sopenharmony_ci ldrb r2, [r0, #VLOCK_OWNER_OFFSET] 8462306a36Sopenharmony_ci eor r0, r1, r2 @ zero if I won, else nonzero 8562306a36Sopenharmony_ci bx lr 8662306a36Sopenharmony_ci 8762306a36Sopenharmony_citrylock_fail: 8862306a36Sopenharmony_ci voting_end r0, r1, r2 8962306a36Sopenharmony_ci mov r0, #1 @ nonzero indicates that I lost 9062306a36Sopenharmony_ci bx lr 9162306a36Sopenharmony_ciENDPROC(vlock_trylock) 9262306a36Sopenharmony_ci 9362306a36Sopenharmony_ci@ r0: lock structure base 9462306a36Sopenharmony_ciENTRY(vlock_unlock) 9562306a36Sopenharmony_ci dmb 9662306a36Sopenharmony_ci mov r1, #VLOCK_OWNER_NONE 9762306a36Sopenharmony_ci strb r1, [r0, #VLOCK_OWNER_OFFSET] 9862306a36Sopenharmony_ci dsb st 9962306a36Sopenharmony_ci sev 10062306a36Sopenharmony_ci bx lr 10162306a36Sopenharmony_ciENDPROC(vlock_unlock) 102