powerpc: Improve resolution of VDSO clock_gettime

Currently the clock_gettime implementation in the VDSO produces a
result with microsecond resolution for the cases that are handled
without a system call, i.e. CLOCK_REALTIME and CLOCK_MONOTONIC.  The
nanoseconds field of the result is obtained by computing a
microseconds value and multiplying by 1000.

This changes the code in the VDSO to do the computation for
clock_gettime with nanosecond resolution.  That means that the
resolution of the result will ultimately depend on the timebase
frequency.

Because the timestamp in the VDSO datapage (stamp_xsec, the real time
corresponding to the timebase count in tb_orig_stamp) is in units of
2^-20 seconds, it doesn't have sufficient resolution for computing a
result with nanosecond resolution.  Therefore this adds a copy of
xtime to the VDSO datapage and updates it in update_gtod() along with
the other time-related fields.

Signed-off-by: Paul Mackerras <paulus@samba.org>

5 files changed, 206 insertions, 148 deletions

diff --git a/arch/powerpc/include/asm/vdso_datapage.h b/arch/powerpc/include/asm/vdso_datapage.h
index f01393224b52..13c2c283e178 100644
--- a/arch/powerpc/include/asm/vdso_datapage.h
+++ b/arch/powerpc/include/asm/vdso_datapage.h
@@ -39,6 +39,7 @@
 #ifndef __ASSEMBLY__
 
 #include <linux/unistd.h>
+#include <linux/time.h>
 
 #define SYSCALL_MAP_SIZE      ((__NR_syscalls + 31) / 32)
 
@@ -83,6 +84,7 @@ struct vdso_data {
         __u32 icache_log_block_size;            /* L1 i-cache log block size */
         __s32 wtom_clock_sec;                   /* Wall to monotonic clock */
         __s32 wtom_clock_nsec;
+        struct timespec stamp_xtime;    /* xtime as at tb_orig_stamp */
         __u32 syscall_map_64[SYSCALL_MAP_SIZE]; /* map of syscalls  */
         __u32 syscall_map_32[SYSCALL_MAP_SIZE]; /* map of syscalls */
 };
@@ -102,6 +104,7 @@ struct vdso_data {
         __u32 tz_dsttime;               /* Type of dst correction       0x5C */
         __s32 wtom_clock_sec;                   /* Wall to monotonic clock */
         __s32 wtom_clock_nsec;
+        struct timespec stamp_xtime;    /* xtime as at tb_orig_stamp */
         __u32 syscall_map_32[SYSCALL_MAP_SIZE]; /* map of syscalls */
         __u32 dcache_block_size;        /* L1 d-cache block size     */
         __u32 icache_block_size;        /* L1 i-cache block size     */
diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-offsets.c
index 75c5dd0138fd..050abfd5c17c 100644
--- a/arch/powerpc/kernel/asm-offsets.c
+++ b/arch/powerpc/kernel/asm-offsets.c
@@ -306,6 +306,7 @@ int main(void)
         DEFINE(CFG_SYSCALL_MAP32, offsetof(struct vdso_data, syscall_map_32));
         DEFINE(WTOM_CLOCK_SEC, offsetof(struct vdso_data, wtom_clock_sec));
         DEFINE(WTOM_CLOCK_NSEC, offsetof(struct vdso_data, wtom_clock_nsec));
+        DEFINE(STAMP_XTIME, offsetof(struct vdso_data, stamp_xtime));
         DEFINE(CFG_ICACHE_BLOCKSZ, offsetof(struct vdso_data, icache_block_size));
         DEFINE(CFG_DCACHE_BLOCKSZ, offsetof(struct vdso_data, dcache_block_size));
         DEFINE(CFG_ICACHE_LOGBLOCKSZ, offsetof(struct vdso_data, icache_log_block_size));
diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c
index e2ee66b5831d..8389c5be149c 100644
--- a/arch/powerpc/kernel/time.c
+++ b/arch/powerpc/kernel/time.c
@@ -456,6 +456,7 @@ static inline void update_gtod(u64 new_tb_stamp, u64 new_stamp_xsec,
         vdso_data->tb_to_xs = new_tb_to_xs;
         vdso_data->wtom_clock_sec = wall_to_monotonic.tv_sec;
         vdso_data->wtom_clock_nsec = wall_to_monotonic.tv_nsec;
+        vdso_data->stamp_xtime = xtime;
         smp_wmb();
         ++(vdso_data->tb_update_count);
 }
diff --git a/arch/powerpc/kernel/vdso32/gettimeofday.S b/arch/powerpc/kernel/vdso32/gettimeofday.S
index 72ca26df457e..ee038d4bf252 100644
--- a/arch/powerpc/kernel/vdso32/gettimeofday.S
+++ b/arch/powerpc/kernel/vdso32/gettimeofday.S
@@ -16,6 +16,13 @@
 #include <asm/asm-offsets.h>
 #include <asm/unistd.h>
 
+/* Offset for the low 32-bit part of a field of long type */
+#ifdef CONFIG_PPC64
+#define LOPART  4
+#else
+#define LOPART  0
+#endif
+
         .text
 /*
  * Exact prototype of gettimeofday
@@ -90,101 +97,53 @@ V_FUNCTION_BEGIN(__kernel_clock_gettime)
 
         mflr    r12                     /* r12 saves lr */
   .cfi_register lr,r12
-        mr      r10,r3                  /* r10 saves id */
         mr      r11,r4                  /* r11 saves tp */
         bl      __get_datapage@local    /* get data page */
         mr      r9,r3                   /* datapage ptr in r9 */
-        beq     cr1,50f                 /* if monotonic -> jump there */
-
-        /*
-         * CLOCK_REALTIME
-         */
-
-        bl      __do_get_xsec@local     /* get xsec from tb & kernel */
-        bne-    98f                     /* out of line -> do syscall */
-
-        /* seconds are xsec >> 20 */
-        rlwinm  r5,r4,12,20,31
-        rlwimi  r5,r3,12,0,19
-        stw     r5,TSPC32_TV_SEC(r11)
 
-        /* get remaining xsec and convert to nsec. we scale
-         * up remaining xsec by 12 bits and get the top 32 bits
-         * of the multiplication, then we multiply by 1000
-         */
-        rlwinm  r5,r4,12,0,19
-        lis     r6,1000000@h
-        ori     r6,r6,1000000@l
-        mulhwu  r5,r5,r6
-        mulli   r5,r5,1000
-        stw     r5,TSPC32_TV_NSEC(r11)
-        mtlr    r12
-        crclr   cr0*4+so
-        li      r3,0
-        blr
+50:     bl      __do_get_tspec@local    /* get sec/nsec from tb & kernel */
+        bne     cr1,80f                 /* not monotonic -> all done */
 
         /*
          * CLOCK_MONOTONIC
          */
 
-50:     bl      __do_get_xsec@local     /* get xsec from tb & kernel */
-        bne-    98f                     /* out of line -> do syscall */
-
-        /* seconds are xsec >> 20 */
-        rlwinm  r6,r4,12,20,31
-        rlwimi  r6,r3,12,0,19
-
-        /* get remaining xsec and convert to nsec. we scale
-         * up remaining xsec by 12 bits and get the top 32 bits
-         * of the multiplication, then we multiply by 1000
-         */
-        rlwinm  r7,r4,12,0,19
-        lis     r5,1000000@h
-        ori     r5,r5,1000000@l
-        mulhwu  r7,r7,r5
-        mulli   r7,r7,1000
-
         /* now we must fixup using wall to monotonic. We need to snapshot
          * that value and do the counter trick again. Fortunately, we still
          * have the counter value in r8 that was returned by __do_get_xsec.
-         * At this point, r6,r7 contain our sec/nsec values, r3,r4 and r5
-         * can be used
+         * At this point, r3,r4 contain our sec/nsec values, r5 and r6
+         * can be used, r7 contains NSEC_PER_SEC.
          */
 
-        lwz     r3,WTOM_CLOCK_SEC(r9)
-        lwz     r4,WTOM_CLOCK_NSEC(r9)
+        lwz     r5,WTOM_CLOCK_SEC(r9)
+        lwz     r6,WTOM_CLOCK_NSEC(r9)
 
-        /* We now have our result in r3,r4. We create a fake dependency
-         * on that result and re-check the counter
+        /* We now have our offset in r5,r6. We create a fake dependency
+         * on that value and re-check the counter
          */
-        or      r5,r4,r3
-        xor     r0,r5,r5
+        or      r0,r6,r5
+        xor     r0,r0,r0
         add     r9,r9,r0
-#ifdef CONFIG_PPC64
-        lwz     r0,(CFG_TB_UPDATE_COUNT+4)(r9)
-#else
-        lwz     r0,(CFG_TB_UPDATE_COUNT)(r9)
-#endif
+        lwz     r0,(CFG_TB_UPDATE_COUNT+LOPART)(r9)
         cmpl    cr0,r8,r0               /* check if updated */
         bne-    50b
 
-        /* Calculate and store result. Note that this mimmics the C code,
+        /* Calculate and store result. Note that this mimics the C code,
          * which may cause funny results if nsec goes negative... is that
          * possible at all ?
          */
-        add     r3,r3,r6
-        add     r4,r4,r7
-        lis     r5,NSEC_PER_SEC@h
-        ori     r5,r5,NSEC_PER_SEC@l
-        cmpl    cr0,r4,r5
-        cmpli   cr1,r4,0
+        add     r3,r3,r5
+        add     r4,r4,r6
+        cmpw    cr0,r4,r7
+        cmpwi   cr1,r4,0
         blt     1f
-        subf    r4,r5,r4
+        subf    r4,r7,r4
         addi    r3,r3,1
-1:      bge     cr1,1f
+1:      bge     cr1,80f
         addi    r3,r3,-1
-        add     r4,r4,r5
-1:      stw     r3,TSPC32_TV_SEC(r11)
+        add     r4,r4,r7
+
+80:     stw     r3,TSPC32_TV_SEC(r11)
         stw     r4,TSPC32_TV_NSEC(r11)
 
         mtlr    r12
@@ -195,10 +154,6 @@ V_FUNCTION_BEGIN(__kernel_clock_gettime)
         /*
          * syscall fallback
          */
-98:
-        mtlr    r12
-        mr      r3,r10
-        mr      r4,r11
 99:
         li      r0,__NR_clock_gettime
         sc
@@ -254,11 +209,7 @@ __do_get_xsec:
         /* Check for update count & load values. We use the low
          * order 32 bits of the update count
          */
-#ifdef CONFIG_PPC64
-1:      lwz     r8,(CFG_TB_UPDATE_COUNT+4)(r9)
-#else
-1:      lwz     r8,(CFG_TB_UPDATE_COUNT)(r9)
-#endif
+1:      lwz     r8,(CFG_TB_UPDATE_COUNT+LOPART)(r9)
         andi.   r0,r8,1                 /* pending update ? loop */
         bne-    1b
         xor     r0,r8,r8                /* create dependency */
@@ -305,11 +256,7 @@ __do_get_xsec:
         or      r6,r4,r3
         xor     r0,r6,r6
         add     r9,r9,r0
-#ifdef CONFIG_PPC64
-        lwz     r0,(CFG_TB_UPDATE_COUNT+4)(r9)
-#else
-        lwz     r0,(CFG_TB_UPDATE_COUNT)(r9)
-#endif
+        lwz     r0,(CFG_TB_UPDATE_COUNT+LOPART)(r9)
         cmpl    cr0,r8,r0               /* check if updated */
         bne-    1b
 
@@ -322,3 +269,98 @@ __do_get_xsec:
          */
 3:      blr
   .cfi_endproc
+
+/*
+ * This is the core of clock_gettime(), it returns the current
+ * time in seconds and nanoseconds in r3 and r4.
+ * It expects the datapage ptr in r9 and doesn't clobber it.
+ * It clobbers r0, r5, r6, r10 and returns NSEC_PER_SEC in r7.
+ * On return, r8 contains the counter value that can be reused.
+ * This clobbers cr0 but not any other cr field.
+ */
+__do_get_tspec:
+  .cfi_startproc
+        /* Check for update count & load values. We use the low
+         * order 32 bits of the update count
+         */
+1:      lwz     r8,(CFG_TB_UPDATE_COUNT+LOPART)(r9)
+        andi.   r0,r8,1                 /* pending update ? loop */
+        bne-    1b
+        xor     r0,r8,r8                /* create dependency */
+        add     r9,r9,r0
+
+        /* Load orig stamp (offset to TB) */
+        lwz     r5,CFG_TB_ORIG_STAMP(r9)
+        lwz     r6,(CFG_TB_ORIG_STAMP+4)(r9)
+
+        /* Get a stable TB value */
+2:      mftbu   r3
+        mftbl   r4
+        mftbu   r0
+        cmpl    cr0,r3,r0
+        bne-    2b
+
+        /* Subtract tb orig stamp and shift left 12 bits.
+         */
+        subfc   r7,r6,r4
+        subfe   r0,r5,r3
+        slwi    r0,r0,12
+        rlwimi. r0,r7,12,20,31
+        slwi    r7,r7,12
+
+        /* Load scale factor & do multiplication */
+        lwz     r5,CFG_TB_TO_XS(r9)     /* load values */
+        lwz     r6,(CFG_TB_TO_XS+4)(r9)
+        mulhwu  r3,r7,r6
+        mullw   r10,r7,r5
+        mulhwu  r4,r7,r5
+        addc    r10,r3,r10
+        li      r3,0
+
+        beq+    4f                      /* skip high part computation if 0 */
+        mulhwu  r3,r0,r5
+        mullw   r7,r0,r5
+        mulhwu  r5,r0,r6
+        mullw   r6,r0,r6
+        adde    r4,r4,r7
+        addze   r3,r3
+        addc    r4,r4,r5
+        addze   r3,r3
+        addc    r10,r10,r6
+
+4:      addze   r4,r4                   /* add in carry */
+        lis     r7,NSEC_PER_SEC@h
+        ori     r7,r7,NSEC_PER_SEC@l
+        mulhwu  r4,r4,r7                /* convert to nanoseconds */
+
+        /* At this point, we have seconds & nanoseconds since the xtime
+         * stamp in r3+CA and r4.  Load & add the xtime stamp.
+         */
+#ifdef CONFIG_PPC64
+        lwz     r5,STAMP_XTIME+TSPC64_TV_SEC+LOPART(r9)
+        lwz     r6,STAMP_XTIME+TSPC64_TV_NSEC+LOPART(r9)
+#else
+        lwz     r5,STAMP_XTIME+TSPC32_TV_SEC(r9)
+        lwz     r6,STAMP_XTIME+TSPC32_TV_NSEC(r9)
+#endif
+        add     r4,r4,r6
+        adde    r3,r3,r5
+
+        /* We now have our result in r3,r4. We create a fake dependency
+         * on that result and re-check the counter
+         */
+        or      r6,r4,r3
+        xor     r0,r6,r6
+        add     r9,r9,r0
+        lwz     r0,(CFG_TB_UPDATE_COUNT+LOPART)(r9)
+        cmpl    cr0,r8,r0               /* check if updated */
+        bne-    1b
+
+        /* check for nanosecond overflow and adjust if necessary */
+        cmpw    r4,r7
+        bltlr                           /* all done if no overflow */
+        subf    r4,r7,r4                /* adjust if overflow */
+        addi    r3,r3,1
+
+        blr
+  .cfi_endproc
diff --git a/arch/powerpc/kernel/vdso64/gettimeofday.S b/arch/powerpc/kernel/vdso64/gettimeofday.S
index c6401f9e37f1..262cd5857a56 100644
--- a/arch/powerpc/kernel/vdso64/gettimeofday.S
+++ b/arch/powerpc/kernel/vdso64/gettimeofday.S
@@ -75,90 +75,49 @@ V_FUNCTION_BEGIN(__kernel_clock_gettime)
 
         mflr    r12                     /* r12 saves lr */
   .cfi_register lr,r12
-        mr      r10,r3                  /* r10 saves id */
         mr      r11,r4                  /* r11 saves tp */
         bl      V_LOCAL_FUNC(__get_datapage)    /* get data page */
-        beq     cr1,50f                 /* if monotonic -> jump there */
-
-        /*
-         * CLOCK_REALTIME
-         */
-
-        bl      V_LOCAL_FUNC(__do_get_xsec)     /* get xsec from tb & kernel */
-
-        lis     r7,15                   /* r7 = 1000000 = USEC_PER_SEC */
-        ori     r7,r7,16960
-        rldicl  r5,r4,44,20             /* r5 = sec = xsec / XSEC_PER_SEC */
-        rldicr  r6,r5,20,43             /* r6 = sec * XSEC_PER_SEC */
-        std     r5,TSPC64_TV_SEC(r11)   /* store sec in tv */
-        subf    r0,r6,r4                /* r0 = xsec = (xsec - r6) */
-        mulld   r0,r0,r7                /* usec = (xsec * USEC_PER_SEC) /
-                                         * XSEC_PER_SEC
-                                         */
-        rldicl  r0,r0,44,20
-        mulli   r0,r0,1000              /* nsec = usec * 1000 */
-        std     r0,TSPC64_TV_NSEC(r11)  /* store nsec in tp */
-
-        mtlr    r12
-        crclr   cr0*4+so
-        li      r3,0
-        blr
+50:     bl      V_LOCAL_FUNC(__do_get_tspec)    /* get time from tb & kernel */
+        bne     cr1,80f                 /* if not monotonic, all done */
 
         /*
          * CLOCK_MONOTONIC
          */
 
-50:     bl      V_LOCAL_FUNC(__do_get_xsec)     /* get xsec from tb & kernel */
-
-        lis     r7,15                   /* r7 = 1000000 = USEC_PER_SEC */
-        ori     r7,r7,16960
-        rldicl  r5,r4,44,20             /* r5 = sec = xsec / XSEC_PER_SEC */
-        rldicr  r6,r5,20,43             /* r6 = sec * XSEC_PER_SEC */
-        subf    r0,r6,r4                /* r0 = xsec = (xsec - r6) */
-        mulld   r0,r0,r7                /* usec = (xsec * USEC_PER_SEC) /
-                                         * XSEC_PER_SEC
-                                         */
-        rldicl  r6,r0,44,20
-        mulli   r6,r6,1000              /* nsec = usec * 1000 */
-
         /* now we must fixup using wall to monotonic. We need to snapshot
          * that value and do the counter trick again. Fortunately, we still
-         * have the counter value in r8 that was returned by __do_get_xsec.
-         * At this point, r5,r6 contain our sec/nsec values.
-         * can be used
+         * have the counter value in r8 that was returned by __do_get_tspec.
+         * At this point, r4,r5 contain our sec/nsec values.
          */
 
-        lwa     r4,WTOM_CLOCK_SEC(r3)
-        lwa     r7,WTOM_CLOCK_NSEC(r3)
+        lwa     r6,WTOM_CLOCK_SEC(r3)
+        lwa     r9,WTOM_CLOCK_NSEC(r3)
 
-        /* We now have our result in r4,r7. We create a fake dependency
+        /* We now have our result in r6,r9. We create a fake dependency
          * on that result and re-check the counter
          */
-        or      r9,r4,r7
-        xor     r0,r9,r9
+        or      r0,r6,r9
+        xor     r0,r0,r0
         add     r3,r3,r0
         ld      r0,CFG_TB_UPDATE_COUNT(r3)
         cmpld   cr0,r0,r8               /* check if updated */
         bne-    50b
 
-        /* Calculate and store result. Note that this mimmics the C code,
-         * which may cause funny results if nsec goes negative... is that
-         * possible at all ?
+        /* Add wall->monotonic offset and check for overflow or underflow.
          */
-        add     r4,r4,r5
-        add     r7,r7,r6
-        lis     r9,NSEC_PER_SEC@h
-        ori     r9,r9,NSEC_PER_SEC@l
-        cmpl    cr0,r7,r9
-        cmpli   cr1,r7,0
+        add     r4,r4,r6
+        add     r5,r5,r9
+        cmpd    cr0,r5,r7
+        cmpdi   cr1,r5,0
         blt     1f
-        subf    r7,r9,r7
+        subf    r5,r7,r5
         addi    r4,r4,1
-1:      bge     cr1,1f
+1:      bge     cr1,80f
         addi    r4,r4,-1
-        add     r7,r7,r9
-1:      std     r4,TSPC64_TV_SEC(r11)
-        std     r7,TSPC64_TV_NSEC(r11)
+        add     r5,r5,r7
+
+80:     std     r4,TSPC64_TV_SEC(r11)
+        std     r5,TSPC64_TV_NSEC(r11)
 
         mtlr    r12
         crclr   cr0*4+so
@@ -168,10 +127,6 @@ V_FUNCTION_BEGIN(__kernel_clock_gettime)
         /*
          * syscall fallback
          */
-98:
-        mtlr    r12
-        mr      r3,r10
-        mr      r4,r11
 99:
         li      r0,__NR_clock_gettime
         sc
@@ -253,3 +208,59 @@ V_FUNCTION_BEGIN(__do_get_xsec)
         blr
   .cfi_endproc
 V_FUNCTION_END(__do_get_xsec)
+
+/*
+ * This is the core of clock_gettime(), it returns the current
+ * time in seconds and nanoseconds in r4 and r5.
+ * It expects the datapage ptr in r3 and doesn't clobber it.
+ * It clobbers r0 and r6 and returns NSEC_PER_SEC in r7.
+ * On return, r8 contains the counter value that can be reused.
+ * This clobbers cr0 but not any other cr field.
+ */
+V_FUNCTION_BEGIN(__do_get_tspec)
+  .cfi_startproc
+        /* check for update count & load values */
+1:      ld      r8,CFG_TB_UPDATE_COUNT(r3)
+        andi.   r0,r8,1                 /* pending update ? loop */
+        bne-    1b
+        xor     r0,r8,r8                /* create dependency */
+        add     r3,r3,r0
+
+        /* Get TB & offset it. We use the MFTB macro which will generate
+         * workaround code for Cell.
+         */
+        MFTB(r7)
+        ld      r9,CFG_TB_ORIG_STAMP(r3)
+        subf    r7,r9,r7
+
+        /* Scale result */
+        ld      r5,CFG_TB_TO_XS(r3)
+        sldi    r7,r7,12                /* compute time since stamp_xtime */
+        mulhdu  r6,r7,r5                /* in units of 2^-32 seconds */
+
+        /* Add stamp since epoch */
+        ld      r4,STAMP_XTIME+TSPC64_TV_SEC(r3)
+        ld      r5,STAMP_XTIME+TSPC64_TV_NSEC(r3)
+        or      r0,r4,r5
+        or      r0,r0,r6
+        xor     r0,r0,r0
+        add     r3,r3,r0
+        ld      r0,CFG_TB_UPDATE_COUNT(r3)
+        cmpld   r0,r8                   /* check if updated */
+        bne-    1b                      /* reload if so */
+
+        /* convert to seconds & nanoseconds and add to stamp */
+        lis     r7,NSEC_PER_SEC@h
+        ori     r7,r7,NSEC_PER_SEC@l
+        mulhwu  r0,r6,r7                /* compute nanoseconds and */
+        srdi    r6,r6,32                /* seconds since stamp_xtime */
+        clrldi  r0,r0,32
+        add     r5,r5,r0                /* add nanoseconds together */
+        cmpd    r5,r7                   /* overflow? */
+        add     r4,r4,r6
+        bltlr                           /* all done if no overflow */
+        subf    r5,r7,r5                /* if overflow, adjust */
+        addi    r4,r4,1
+        blr
+  .cfi_endproc
+V_FUNCTION_END(__do_get_tspec)