arch/tile/include/asm/percpu.h

   1 /*
   2  * Copyright 2010 Tilera Corporation. All Rights Reserved.
   3  *
   4  *   This program is free software; you can redistribute it and/or
   5  *   modify it under the terms of the GNU General Public License
   6  *   as published by the Free Software Foundation, version 2.
   7  *
   8  *   This program is distributed in the hope that it will be useful, but
   9  *   WITHOUT ANY WARRANTY; without even the implied warranty of
  10  *   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
  11  *   NON INFRINGEMENT.  See the GNU General Public License for
  12  *   more details.
  13  */
  14
  15 #ifndef _ASM_TILE_PERCPU_H
  16 #define _ASM_TILE_PERCPU_H
  17
  18 register unsigned long my_cpu_offset_reg asm("tp");
  19
  20 #ifdef CONFIG_PREEMPT
  21 /*
  22  * For full preemption, we can't just use the register variable
  23  * directly, since we need barrier() to hazard against it, causing the
  24  * compiler to reload anything computed from a previous "tp" value.
  25  * But we also don't want to use volatile asm, since we'd like the
  26  * compiler to be able to cache the value across multiple percpu reads.
  27  * So we use a fake stack read as a hazard against barrier().
  28  * The 'U' constraint is like 'm' but disallows postincrement.
  29  */
  30 static inline unsigned long __my_cpu_offset(void)
  31 {
  32         unsigned long tp;
  33         register unsigned long *sp asm("sp");
  34         asm("move %0, tp" : "=r" (tp) : "U" (*sp));
  35         return tp;
  36 }
  37 #define __my_cpu_offset __my_cpu_offset()
  38 #else
  39 /*
  40  * We don't need to hazard against barrier() since "tp" doesn't ever
  41  * change with PREEMPT_NONE, and with PREEMPT_VOLUNTARY it only
  42  * changes at function call points, at which we are already re-reading
  43  * the value of "tp" due to "my_cpu_offset_reg" being a global variable.
  44  */
  45 #define __my_cpu_offset my_cpu_offset_reg
  46 #endif
  47
  48 #define set_my_cpu_offset(tp) (my_cpu_offset_reg = (tp))
  49
  50 #include <asm-generic/percpu.h>
  51
  52 #endif /* _ASM_TILE_PERCPU_H */