MIPS: VDSO: Add implementation of clock_gettime() fallback

This patch adds clock_gettime_fallback() function that wraps assembly
invocation of clock_gettime() syscall using __NR_clock_gettime.

This function is used if pure VDSO implementation of clock_gettime()
does not succeed for any reason. For example, it is called if the
clkid parameter of clock_gettime() is not one of the clkids listed
in the switch-case block of the function __vdso_clock_gettime()
(one such case for clkid is CLOCK_BOOTIME).

If syscall invocation via __NR_clock_gettime fails, register a3 will
be set. So, after the syscall, register a3 is tested and the return
value is negated if it's set.

Signed-off-by: Goran Ferenc <goran.ferenc@imgtec.com>
Signed-off-by: Miodrag Dinic <miodrag.dinic@imgtec.com>
Signed-off-by: Aleksandar Markovic <aleksandar.markovic@imgtec.com>
Cc: Douglas Leung <douglas.leung@imgtec.com>
Cc: James Hogan <james.hogan@imgtec.com>
Cc: Paul Burton <paul.burton@imgtec.com>
Cc: Petar Jovanovic <petar.jovanovic@imgtec.com>
Cc: Raghu Gandham <raghu.gandham@imgtec.com>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/16639/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

diff --git a/arch/mips/vdso/gettimeofday.c b/arch/mips/vdso/gettimeofday.c
index fd7d433970bf614117f55cdb3262c8ff5e370a56..5f6337545ee2a56f091ebbc56cdbeb5e29c86b37 100644 (file)
--- a/arch/mips/vdso/gettimeofday.c
+++ b/arch/mips/vdso/gettimeofday.c
@@ -20,6 +20,24 @@
 #include <asm/unistd.h>
 #include <asm/vdso.h>
 
+static __always_inline long clock_gettime_fallback(clockid_t _clkid,
+                                          struct timespec *_ts)
+{
+       register struct timespec *ts asm("a1") = _ts;
+       register clockid_t clkid asm("a0") = _clkid;
+       register long ret asm("v0");
+       register long nr asm("v0") = __NR_clock_gettime;
+       register long error asm("a3");
+
+       asm volatile(
+       "       syscall\n"
+       : "=r" (ret), "=r" (error)
+       : "r" (clkid), "r" (ts), "r" (nr)
+       : "memory");
+
+       return error ? -ret : ret;
+}
+
 static __always_inline int do_realtime_coarse(struct timespec *ts,
                                              const union mips_vdso_data *data)
 {
@@ -207,7 +225,7 @@ int __vdso_gettimeofday(struct timeval *tv, struct timezone *tz)
 int __vdso_clock_gettime(clockid_t clkid, struct timespec *ts)
 {
        const union mips_vdso_data *data = get_vdso_data();
-       int ret;
+       int ret = -1;
 
        switch (clkid) {
        case CLOCK_REALTIME_COARSE:
@@ -223,10 +241,11 @@ int __vdso_clock_gettime(clockid_t clkid, struct timespec *ts)
                ret = do_monotonic(ts, data);
                break;
        default:
-               ret = -ENOSYS;
                break;
        }
 
-       /* If we return -ENOSYS libc should fall back to a syscall. */
+       if (ret)
+               ret = clock_gettime_fallback(clkid, ts);
+
        return ret;
 }