arm: vdso: do calculations outside reader loops

Take an effort to recode the arm64 vdso code from assembler to C previously submitted by Andrew Pinski <[email protected]>, rework it for use in both arm and arm64, overlapping any optimizations for each architecture. But instead of landing it in arm64, land the result into lib/vdso and unify both implementations to simplify future maintenance.

In variable timer reading loops, pick up just the values until all are synchronized, then outside of loop pick up cntvct and perform calculations to determine final offset, shifted and multiplied output value.

This replaces get_ns with get_clock_shifted_nsec as cntvct reader.

v2:
- split first CL into 5 of 7 pieces

v4:
- split into two, moving ARCH_CLOCK_FIXED_MASK to later
- update commit message to reflect overall reasoning
- adjust for dropping forced inline
- replace typeof() with types vdso_wtm_clock_nsec_t, vdso_xtime_clock_sec and __kernel_time_t.

v5:
- drop including linux/time.h in favour of uapi/linux/time.h in vgettimeofday.c to limit architectural includes.
- add linux/time.h to compiler.h for NSEC_PER_SEC definition.
- replace last timespec_add_ns with __iter_div_u64_rem.

---
 arch/arm/include/asm/vdso_datapage.h | 18 ++++++--
 arch/arm/vdso/compiler.h             |  1 +
 arch/arm/vdso/vgettimeofday.c        | 90 ++++++++++++++++++++++++------------
 3 files changed, 76 insertions(+), 33 deletions(-)

index fa3e1856244d..8dd7303db4ec 100644
@@ -24,6 +24,16 @@
 
 #include <asm/page.h>
 
+#ifndef _VDSO_WTM_CLOCK_SEC_T
+#define _VDSO_WTM_CLOCK_SEC_T
+typedef u32 vdso_wtm_clock_nsec_t;
+#endif
+
+#ifndef _VDSO_XTIME_CLOCK_SEC_T
+#define _VDSO_XTIME_CLOCK_SEC_T
+typedef u32 vdso_xtime_clock_sec_t;
+#endif
+
 /* Try to be cache-friendly on systems that don't implement the
  * generic timer: fit the unconditionally updated fields in the first
  * 32 bytes.

@@ -35,9 +45,11 @@ struct vdso_data {
 	u32 xtime_coarse_sec;	/* coarse time */
 	u32 xtime_coarse_nsec;
 
-	u32 wtm_clock_sec;	/* wall to monotonic offset */
-	u32 wtm_clock_nsec;
-	u32 xtime_clock_sec;	/* CLOCK_REALTIME - seconds */
+	/* wall to monotonic offset */
+	u32 wtm_clock_sec;
+	vdso_wtm_clock_nsec_t	wtm_clock_nsec;
+	/* CLOCK_REALTIME - seconds */
+	vdso_xtime_clock_sec_t	xtime_clock_sec;
 	u32 cs_mono_mult;	/* clocksource multiplier */
 
 	u64 cs_cycle_last;	/* last cycle value */

index af24502797e8..3edddb705a1b 100644
@@ -27,6 +27,7 @@
 #include <asm/processor.h>	/* for cpu_relax()			*/
 #include <asm/unistd.h>
 #include <linux/compiler.h>
+#include <linux/time.h>		/* for NSEC_PER_SEC			*/
 
 #ifndef CONFIG_AEABI
 #error This code depends on AEABI system call conventions

2.15.0.403.gc27cc4dac6-goog