diff options
Diffstat (limited to 'arch')
| -rw-r--r-- | arch/mips/include/asm/barrier.h | 96 |
1 files changed, 96 insertions, 0 deletions
diff --git a/arch/mips/include/asm/barrier.h b/arch/mips/include/asm/barrier.h index d296633..a5eb1bb 100644 --- a/arch/mips/include/asm/barrier.h +++ b/arch/mips/include/asm/barrier.h @@ -10,6 +10,102 @@ #include <asm/addrspace.h> +/* + * Sync types defined by the MIPS architecture (document MD00087 table 6.5) + * These values are used with the sync instruction to perform memory barriers. + * Types of ordering guarantees available through the SYNC instruction: + * - Completion Barriers + * - Ordering Barriers + * As compared to the completion barrier, the ordering barrier is a + * lighter-weight operation as it does not require the specified instructions + * before the SYNC to be already completed. Instead it only requires that those + * specified instructions which are subsequent to the SYNC in the instruction + * stream are never re-ordered for processing ahead of the specified + * instructions which are before the SYNC in the instruction stream. + * This potentially reduces how many cycles the barrier instruction must stall + * before it completes. + * Implementations that do not use any of the non-zero values of stype to define + * different barriers, such as ordering barriers, must make those stype values + * act the same as stype zero. + */ + +/* + * Completion barriers: + * - Every synchronizable specified memory instruction (loads or stores or both) + * that occurs in the instruction stream before the SYNC instruction must be + * already globally performed before any synchronizable specified memory + * instructions that occur after the SYNC are allowed to be performed, with + * respect to any other processor or coherent I/O module. + * + * - The barrier does not guarantee the order in which instruction fetches are + * performed. + * + * - A stype value of zero will always be defined such that it performs the most + * complete set of synchronization operations that are defined.This means + * stype zero always does a completion barrier that affects both loads and + * stores preceding the SYNC instruction and both loads and stores that are + * subsequent to the SYNC instruction. Non-zero values of stype may be defined + * by the architecture or specific implementations to perform synchronization + * behaviors that are less complete than that of stype zero. If an + * implementation does not use one of these non-zero values to define a + * different synchronization behavior, then that non-zero value of stype must + * act the same as stype zero completion barrier. This allows software written + * for an implementation with a lighter-weight barrier to work on another + * implementation which only implements the stype zero completion barrier. + * + * - A completion barrier is required, potentially in conjunction with SSNOP (in + * Release 1 of the Architecture) or EHB (in Release 2 of the Architecture), + * to guarantee that memory reference results are visible across operating + * mode changes. For example, a completion barrier is required on some + * implementations on entry to and exit from Debug Mode to guarantee that + * memory effects are handled correctly. + */ + +/* + * stype 0 - A completion barrier that affects preceding loads and stores and + * subsequent loads and stores. + * Older instructions which must reach the load/store ordering point before the + * SYNC instruction completes: Loads, Stores + * Younger instructions which must reach the load/store ordering point only + * after the SYNC instruction completes: Loads, Stores + * Older instructions which must be globally performed when the SYNC instruction + * completes: Loads, Stores + */ +#define STYPE_SYNC 0x0 + +/* + * Ordering barriers: + * - Every synchronizable specified memory instruction (loads or stores or both) + * that occurs in the instruction stream before the SYNC instruction must + * reach a stage in the load/store datapath after which no instruction + * re-ordering is possible before any synchronizable specified memory + * instruction which occurs after the SYNC instruction in the instruction + * stream reaches the same stage in the load/store datapath. + * + * - If any memory instruction before the SYNC instruction in program order, + * generates a memory request to the external memory and any memory + * instruction after the SYNC instruction in program order also generates a + * memory request to external memory, the memory request belonging to the + * older instruction must be globally performed before the time the memory + * request belonging to the younger instruction is globally performed. + * + * - The barrier does not guarantee the order in which instruction fetches are + * performed. + */ + +/* + * stype 0x10 - An ordering barrier that affects preceding loads and stores and + * subsequent loads and stores. + * Older instructions which must reach the load/store ordering point before the + * SYNC instruction completes: Loads, Stores + * Younger instructions which must reach the load/store ordering point only + * after the SYNC instruction completes: Loads, Stores + * Older instructions which must be globally performed when the SYNC instruction + * completes: N/A + */ +#define STYPE_SYNC_MB 0x10 + + #ifdef CONFIG_CPU_HAS_SYNC #define __sync() \ __asm__ __volatile__( \ |