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99 lines
2.2 KiB
99 lines
2.2 KiB
/* SPDX-License-Identifier: GPL-2.0-only */ |
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/* |
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* vlock.S - simple voting lock implementation for ARM |
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* |
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* Created by: Dave Martin, 2012-08-16 |
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* Copyright: (C) 2012-2013 Linaro Limited |
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* |
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* This algorithm is described in more detail in |
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* Documentation/arm/vlocks.rst. |
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*/ |
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#include <linux/linkage.h> |
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#include "vlock.h" |
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/* Select different code if voting flags can fit in a single word. */ |
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#if VLOCK_VOTING_SIZE > 4 |
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#define FEW(x...) |
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#define MANY(x...) x |
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#else |
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#define FEW(x...) x |
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#define MANY(x...) |
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#endif |
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@ voting lock for first-man coordination |
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.macro voting_begin rbase:req, rcpu:req, rscratch:req |
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mov \rscratch, #1 |
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strb \rscratch, [\rbase, \rcpu] |
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dmb |
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.endm |
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.macro voting_end rbase:req, rcpu:req, rscratch:req |
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dmb |
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mov \rscratch, #0 |
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strb \rscratch, [\rbase, \rcpu] |
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dsb st |
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sev |
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.endm |
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/* |
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* The vlock structure must reside in Strongly-Ordered or Device memory. |
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* This implementation deliberately eliminates most of the barriers which |
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* would be required for other memory types, and assumes that independent |
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* writes to neighbouring locations within a cacheline do not interfere |
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* with one another. |
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*/ |
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@ r0: lock structure base |
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@ r1: CPU ID (0-based index within cluster) |
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ENTRY(vlock_trylock) |
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add r1, r1, #VLOCK_VOTING_OFFSET |
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voting_begin r0, r1, r2 |
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ldrb r2, [r0, #VLOCK_OWNER_OFFSET] @ check whether lock is held |
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cmp r2, #VLOCK_OWNER_NONE |
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bne trylock_fail @ fail if so |
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@ Control dependency implies strb not observable before previous ldrb. |
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strb r1, [r0, #VLOCK_OWNER_OFFSET] @ submit my vote |
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voting_end r0, r1, r2 @ implies DMB |
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@ Wait for the current round of voting to finish: |
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MANY( mov r3, #VLOCK_VOTING_OFFSET ) |
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0: |
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MANY( ldr r2, [r0, r3] ) |
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FEW( ldr r2, [r0, #VLOCK_VOTING_OFFSET] ) |
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cmp r2, #0 |
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wfene |
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bne 0b |
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MANY( add r3, r3, #4 ) |
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MANY( cmp r3, #VLOCK_VOTING_OFFSET + VLOCK_VOTING_SIZE ) |
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MANY( bne 0b ) |
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@ Check who won: |
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dmb |
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ldrb r2, [r0, #VLOCK_OWNER_OFFSET] |
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eor r0, r1, r2 @ zero if I won, else nonzero |
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bx lr |
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trylock_fail: |
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voting_end r0, r1, r2 |
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mov r0, #1 @ nonzero indicates that I lost |
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bx lr |
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ENDPROC(vlock_trylock) |
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@ r0: lock structure base |
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ENTRY(vlock_unlock) |
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dmb |
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mov r1, #VLOCK_OWNER_NONE |
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strb r1, [r0, #VLOCK_OWNER_OFFSET] |
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dsb st |
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sev |
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bx lr |
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ENDPROC(vlock_unlock)
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