| /* Copyright (c) 2010 The Regents of the University of California |
| * Barret Rhoden <brho@cs.berkeley.edu> |
| * See LICENSE for details. |
| * |
| * Locking and atomics that are part of the kernel interface. */ |
| |
| #ifndef ROS_INC_ATOMIC_H |
| #define ROS_INC_ATOMIC_H |
| |
| #include <ros/common.h> |
| #include <ros/arch/membar.h> |
| |
| typedef void* atomic_t; |
| |
| /* The seq counters are used by userspace to see if the kernel is updating |
| * something or if something is valid, such as the vcore->pcore mapping. The |
| * way a reader can tell nothing has changed is to read the counter before and |
| * after. If the value has changed, the reader needs to re-read. If the value |
| * is odd, a write is in progress or it is otherwise invalid/locked. */ |
| |
| typedef uint8_t seq_ctr_t; |
| #define SEQCTR_INITIALIZER 0 |
| |
| static inline bool seq_is_locked(seq_ctr_t seq_ctr); |
| static inline bool seqctr_retry(seq_ctr_t old_ctr, seq_ctr_t new_ctr); |
| |
| /* Basic helpers for readers. Ex: |
| * do { |
| * seq_ctr_t seq = kernel_maintained_seq_ctr |
| * read_data_whatever(); |
| * } while (seqctr_retry(seq, kernel_maintained_seq_ctr); |
| */ |
| static inline bool seq_is_locked(seq_ctr_t seq_ctr) |
| { |
| return seq_ctr % 2; |
| } |
| |
| static inline bool seqctr_retry(seq_ctr_t old_ctr, seq_ctr_t new_ctr) |
| { |
| rmb(); /* don't allow protected reads to reorder after the check */ |
| return (seq_is_locked(old_ctr)) || (old_ctr != new_ctr); |
| } |
| |
| #endif /* ROS_INC_ATOMIC_H */ |
