text: /*
   * Copyright (C) 2015 Imagination Technologies
   * Author: Alex Smith <alex.smith@imgtec.com>
   *
   * 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;  either version 2 of the  License, or (at your
   * option) any later version.
   */
  
  #ifndef __ASM_VDSO_H
  #define __ASM_VDSO_H
  
  #include <linux/mm_types.h>
  
  #include <asm/barrier.h>
  
  /**
   * struct mips_vdso_image - Details of a VDSO image.
   * @data: Pointer to VDSO image data (page-aligned).
   * @size: Size of the VDSO image data (page-aligned).
   * @off_sigreturn: Offset of the sigreturn() trampoline.
   * @off_rt_sigreturn: Offset of the rt_sigreturn() trampoline.
   * @mapping: Special mapping structure.
   *
   * This structure contains details of a VDSO image, including the image data
   * and offsets of certain symbols required by the kernel. It is generated as
   * part of the VDSO build process, aside from the mapping page array, which is
   * populated at runtime.
   */
  struct mips_vdso_image {
  	void *data;
  	unsigned long size;
  
  	unsigned long off_sigreturn;
  	unsigned long off_rt_sigreturn;
  
  	struct vm_special_mapping mapping;
  };
  
  /*
   * The following structures are auto-generated as part of the build for each
   * ABI by genvdso, see arch/mips/vdso/Makefile.
   */
  
  extern struct mips_vdso_image vdso_image;
  
  #ifdef CONFIG_MIPS32_O32
  extern struct mips_vdso_image vdso_image_o32;
  #endif
  
  #ifdef CONFIG_MIPS32_N32
  extern struct mips_vdso_image vdso_image_n32;
  #endif
  
  /**
   * union mips_vdso_data - Data provided by the kernel for the VDSO.
   * @xtime_sec:		Current real time (seconds part).
   * @xtime_nsec:		Current real time (nanoseconds part, shifted).
   * @wall_to_mono_sec:	Wall-to-monotonic offset (seconds part).
   * @wall_to_mono_nsec:	Wall-to-monotonic offset (nanoseconds part).
   * @seq_count:		Counter to synchronise updates (odd = updating).
   * @cs_shift:		Clocksource shift value.
   * @clock_mode:		Clocksource to use for time functions.
   * @cs_mult:		Clocksource multiplier value.
   * @cs_cycle_last:	Clock cycle value at last update.
   * @cs_mask:		Clocksource mask value.
   * @tz_minuteswest:	Minutes west of Greenwich (from timezone).
   * @tz_dsttime:		Type of DST correction (from timezone).
   *
   * This structure contains data needed by functions within the VDSO. It is
   * populated by the kernel and mapped read-only into user memory. The time
   * fields are mirrors of internal data from the timekeeping infrastructure.
   *
   * Note: Care should be taken when modifying as the layout must remain the same
   * for both 64- and 32-bit (for 32-bit userland on 64-bit kernel).
   */
  union mips_vdso_data {
  	struct {
  		u64 xtime_sec;
  		u64 xtime_nsec;
  		u64 wall_to_mono_sec;
  		u64 wall_to_mono_nsec;
  		u32 seq_count;
  		u32 cs_shift;
  		u8 clock_mode;
  		u32 cs_mult;
  		u64 cs_cycle_last;
  		u64 cs_mask;
  		s32 tz_minuteswest;
  		s32 tz_dsttime;
  	};
  
  	u8 page[PAGE_SIZE];
  };
  
  static inline u32 vdso_data_read_begin(const union mips_vdso_data *data)
  {
  	u32 seq;
  
  	while (true) {
  		seq = ACCESS_ONCE(data->seq_count);
  		if (likely(!(seq & 1))) {
  			/* Paired with smp_wmb() in vdso_data_write_*(). */
  			smp_rmb();
  			return seq;
  		}
  
  		cpu_relax();
  	}
  }
  
  static inline bool vdso_data_read_retry(const union mips_vdso_data *data,
  					u32 start_seq)
  {
  	/* Paired with smp_wmb() in vdso_data_write_*(). */
  	smp_rmb();
  	return unlikely(data->seq_count != start_seq);
  }
  
  static inline void vdso_data_write_begin(union mips_vdso_data *data)
  {
  	++data->seq_count;
  
  	/* Ensure sequence update is written before other data page values. */
  	smp_wmb();
  }
  
  static inline void vdso_data_write_end(union mips_vdso_data *data)
  {
  	/* Ensure data values are written before updating sequence again. */
  	smp_wmb();
  	++data->seq_count;
  }
  
  #endif /* __ASM_VDSO_H */
  