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Diffstat (limited to 'arch/tile/lib/atomic_asm_32.S')
| -rw-r--r-- | arch/tile/lib/atomic_asm_32.S | 196 |
1 files changed, 196 insertions, 0 deletions
diff --git a/arch/tile/lib/atomic_asm_32.S b/arch/tile/lib/atomic_asm_32.S new file mode 100644 index 0000000..5a5514b --- /dev/null +++ b/arch/tile/lib/atomic_asm_32.S @@ -0,0 +1,196 @@ +/* + * Copyright 2010 Tilera Corporation. All Rights Reserved. + * + * This program is free software; you can redistribute it and/or + * modify it under the terms of the GNU General Public License + * as published by the Free Software Foundation, version 2. + * + * This program is distributed in the hope that it will be useful, but + * WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or + * NON INFRINGEMENT. See the GNU General Public License for + * more details. + * + * Support routines for atomic operations. Each function takes: + * + * r0: address to manipulate + * r1: pointer to atomic lock guarding this operation (for FUTEX_LOCK_REG) + * r2: new value to write, or for cmpxchg/add_unless, value to compare against + * r3: (cmpxchg/xchg_add_unless) new value to write or add; + * (atomic64 ops) high word of value to write + * r4/r5: (cmpxchg64/add_unless64) new value to write or add + * + * The 32-bit routines return a "struct __get_user" so that the futex code + * has an opportunity to return -EFAULT to the user if needed. + * The 64-bit routines just return a "long long" with the value, + * since they are only used from kernel space and don't expect to fault. + * Support for 16-bit ops is included in the framework but we don't provide + * any (x86_64 has an atomic_inc_short(), so we might want to some day). + * + * Note that the caller is advised to issue a suitable L1 or L2 + * prefetch on the address being manipulated to avoid extra stalls. + * In addition, the hot path is on two icache lines, and we start with + * a jump to the second line to make sure they are both in cache so + * that we never stall waiting on icache fill while holding the lock. + * (This doesn't work out with most 64-bit ops, since they consume + * too many bundles, so may take an extra i-cache stall.) + * + * These routines set the INTERRUPT_CRITICAL_SECTION bit, just + * like sys_cmpxchg(), so that NMIs like PERF_COUNT will not interrupt + * the code, just page faults. + * + * If the load or store faults in a way that can be directly fixed in + * the do_page_fault_ics() handler (e.g. a vmalloc reference) we fix it + * directly, return to the instruction that faulted, and retry it. + * + * If the load or store faults in a way that potentially requires us + * to release the atomic lock, then retry (e.g. a migrating PTE), we + * reset the PC in do_page_fault_ics() to the "tns" instruction so + * that on return we will reacquire the lock and restart the op. We + * are somewhat overloading the exception_table_entry notion by doing + * this, since those entries are not normally used for migrating PTEs. + * + * If the main page fault handler discovers a bad address, it will see + * the PC pointing to the "tns" instruction (due to the earlier + * exception_table_entry processing in do_page_fault_ics), and + * re-reset the PC to the fault handler, atomic_bad_address(), which + * effectively takes over from the atomic op and can either return a + * bad "struct __get_user" (for user addresses) or can just panic (for + * bad kernel addresses). + * + * Note that if the value we would store is the same as what we + * loaded, we bypass the load. Other platforms with true atomics can + * make the guarantee that a non-atomic __clear_bit(), for example, + * can safely race with an atomic test_and_set_bit(); this example is + * from bit_spinlock.h in slub_lock() / slub_unlock(). We can't do + * that on Tile since the "atomic" op is really just a + * read/modify/write, and can race with the non-atomic + * read/modify/write. However, if we can short-circuit the write when + * it is not needed, in the atomic case, we avoid the race. + */ + +#include <linux/linkage.h> +#include <asm/atomic.h> +#include <asm/page.h> +#include <asm/processor.h> + + .section .text.atomic,"ax" +ENTRY(__start_atomic_asm_code) + + .macro atomic_op, name, bitwidth, body + .align 64 +STD_ENTRY_SECTION(__atomic\name, .text.atomic) + { + movei r24, 1 + j 4f /* branch to second cache line */ + } +1: { + .ifc \bitwidth,16 + lh r22, r0 + .else + lw r22, r0 + addi r28, r0, 4 + .endif + } + .ifc \bitwidth,64 + lw r23, r28 + .endif + \body /* set r24, and r25 if 64-bit */ + { + seq r26, r22, r24 + seq r27, r23, r25 + } + .ifc \bitwidth,64 + bbnst r27, 2f + .endif + bbs r26, 3f /* skip write-back if it's the same value */ +2: { + .ifc \bitwidth,16 + sh r0, r24 + .else + sw r0, r24 + .endif + } + .ifc \bitwidth,64 + sw r28, r25 + .endif + mf +3: { + move r0, r22 + .ifc \bitwidth,64 + move r1, r23 + .else + move r1, zero + .endif + sw ATOMIC_LOCK_REG_NAME, zero + } + mtspr INTERRUPT_CRITICAL_SECTION, zero + jrp lr +4: { + move ATOMIC_LOCK_REG_NAME, r1 + mtspr INTERRUPT_CRITICAL_SECTION, r24 + } +#ifndef CONFIG_SMP + j 1b /* no atomic locks */ +#else + { + tns r21, ATOMIC_LOCK_REG_NAME + moveli r23, 2048 /* maximum backoff time in cycles */ + } + { + bzt r21, 1b /* branch if lock acquired */ + moveli r25, 32 /* starting backoff time in cycles */ + } +5: mtspr INTERRUPT_CRITICAL_SECTION, zero + mfspr r26, CYCLE_LOW /* get start point for this backoff */ +6: mfspr r22, CYCLE_LOW /* test to see if we've backed off enough */ + sub r22, r22, r26 + slt r22, r22, r25 + bbst r22, 6b + { + mtspr INTERRUPT_CRITICAL_SECTION, r24 + shli r25, r25, 1 /* double the backoff; retry the tns */ + } + { + tns r21, ATOMIC_LOCK_REG_NAME + slt r26, r23, r25 /* is the proposed backoff too big? */ + } + { + bzt r21, 1b /* branch if lock acquired */ + mvnz r25, r26, r23 + } + j 5b +#endif + STD_ENDPROC(__atomic\name) + .ifc \bitwidth,32 + .pushsection __ex_table,"a" + .word 1b, __atomic\name + .word 2b, __atomic\name + .word __atomic\name, __atomic_bad_address + .popsection + .endif + .endm + +atomic_op _cmpxchg, 32, "seq r26, r22, r2; { bbns r26, 3f; move r24, r3 }" +atomic_op _xchg, 32, "move r24, r2" +atomic_op _xchg_add, 32, "add r24, r22, r2" +atomic_op _xchg_add_unless, 32, \ + "sne r26, r22, r2; { bbns r26, 3f; add r24, r22, r3 }" +atomic_op _or, 32, "or r24, r22, r2" +atomic_op _andn, 32, "nor r2, r2, zero; and r24, r22, r2" +atomic_op _xor, 32, "xor r24, r22, r2" + +atomic_op 64_cmpxchg, 64, "{ seq r26, r22, r2; seq r27, r23, r3 }; \ + { bbns r26, 3f; move r24, r4 }; { bbns r27, 3f; move r25, r5 }" +atomic_op 64_xchg, 64, "{ move r24, r2; move r25, r3 }" +atomic_op 64_xchg_add, 64, "{ add r24, r22, r2; add r25, r23, r3 }; \ + slt_u r26, r24, r22; add r25, r25, r26" +atomic_op 64_xchg_add_unless, 64, \ + "{ sne r26, r22, r2; sne r27, r23, r3 }; \ + { bbns r26, 3f; add r24, r22, r4 }; \ + { bbns r27, 3f; add r25, r23, r5 }; \ + slt_u r26, r24, r22; add r25, r25, r26" + + jrp lr /* happy backtracer */ + +ENTRY(__end_atomic_asm_code) |
