/* SPDX-License-Identifier: GPL-2.0 */
  #ifndef __VDSO_HELPERS_H
  #define __VDSO_HELPERS_H
  
  #ifndef __ASSEMBLY__
  
  #include <vdso/datapage.h>
  
  static __always_inline u32 vdso_read_begin(const struct vdso_data *vd)
  {
  	u32 seq;
  
  	while ((seq = READ_ONCE(vd->seq)) & 1)
  		cpu_relax();
  
  	smp_rmb();
  	return seq;
  }
  
  static __always_inline u32 vdso_read_retry(const struct vdso_data *vd,
  					   u32 start)
  {
  	u32 seq;
  
  	smp_rmb();
  	seq = READ_ONCE(vd->seq);
  	return seq != start;
  }
  
  static __always_inline void vdso_write_begin(struct vdso_data *vd)
  {
  	/*
  	 * WRITE_ONCE it is required otherwise the compiler can validly tear
  	 * updates to vd[x].seq and it is possible that the value seen by the
  	 * reader it is inconsistent.
  	 */
  	WRITE_ONCE(vd[CS_HRES_COARSE].seq, vd[CS_HRES_COARSE].seq + 1);
  	WRITE_ONCE(vd[CS_RAW].seq, vd[CS_RAW].seq + 1);
  	smp_wmb();
  }
  
  static __always_inline void vdso_write_end(struct vdso_data *vd)
  {
  	smp_wmb();
  	/*
  	 * WRITE_ONCE it is required otherwise the compiler can validly tear
  	 * updates to vd[x].seq and it is possible that the value seen by the
  	 * reader it is inconsistent.
  	 */
  	WRITE_ONCE(vd[CS_HRES_COARSE].seq, vd[CS_HRES_COARSE].seq + 1);
  	WRITE_ONCE(vd[CS_RAW].seq, vd[CS_RAW].seq + 1);
  }
  
  #endif /* !__ASSEMBLY__ */
  
  #endif /* __VDSO_HELPERS_H */