vdso/helpers: Prepare introduction of struct vdso_clock

To support multiple PTP clocks, the VDSO data structure needs to be
reworked. All clock specific data will end up in struct vdso_clock and in
struct vdso_time_data there will be an array of VDSO clocks. For now,
vdso_clock is simply a define which maps vdso_clock to vdso_time_data.

Prepare all functions which need the pointer to the vdso_clock array to
work well after the structures get reworked. Replace the struct vdso_time_data
pointer with a struct vdso_clock pointer where applicable.

No functional change.

Signed-off-by: Anna-Maria Behnsen <anna-maria@linutronix.de>
Signed-off-by: Nam Cao <namcao@linutronix.de>
Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20250303-vdso-clock-v1-5-c1b5c69a166f@linutronix.de

Author: anna-marialx

include/vdso/helpers.h

@@ -7,49 +7,53 @@
 #include <asm/barrier.h>
 #include <vdso/datapage.h>
 
-static __always_inline u32 vdso_read_begin(const struct vdso_time_data *vd)
+static __always_inline u32 vdso_read_begin(const struct vdso_clock *vc)
 {
 	u32 seq;
 
-	while (unlikely((seq = READ_ONCE(vd->seq)) & 1))
+	while (unlikely((seq = READ_ONCE(vc->seq)) & 1))
 		cpu_relax();
 
 	smp_rmb();
 	return seq;
 }
 
-static __always_inline u32 vdso_read_retry(const struct vdso_time_data *vd,
+static __always_inline u32 vdso_read_retry(const struct vdso_clock *vc,
 					   u32 start)
 {
 	u32 seq;
 
 	smp_rmb();
-	seq = READ_ONCE(vd->seq);
+	seq = READ_ONCE(vc->seq);
 	return seq != start;
 }
 
 static __always_inline void vdso_write_begin(struct vdso_time_data *vd)
 {
+	struct vdso_clock *vc = vd;
+
 	/*
 	 * WRITE_ONCE() is required otherwise the compiler can validly tear
 	 * updates to vd[x].seq and it is possible that the value seen by the
 	 * reader 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);
+	WRITE_ONCE(vc[CS_HRES_COARSE].seq, vc[CS_HRES_COARSE].seq + 1);
+	WRITE_ONCE(vc[CS_RAW].seq, vc[CS_RAW].seq + 1);
 	smp_wmb();
 }
 
 static __always_inline void vdso_write_end(struct vdso_time_data *vd)
 {
+	struct vdso_clock *vc = vd;
+
 	smp_wmb();
 	/*
 	 * WRITE_ONCE() is required otherwise the compiler can validly tear
 	 * updates to vd[x].seq and it is possible that the value seen by the
 	 * reader 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);
+	WRITE_ONCE(vc[CS_HRES_COARSE].seq, vc[CS_HRES_COARSE].seq + 1);
+	WRITE_ONCE(vc[CS_RAW].seq, vc[CS_RAW].seq + 1);
 }
 
 #endif /* !__ASSEMBLY__ */