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From:   Sasha Levin <Alexander.Levin@microsoft.com>
To:     "stable@vger.kernel.org" <stable@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
CC:     Goran Ferenc <goran.ferenc@imgtec.com>,
        Miodrag Dinic <miodrag.dinic@imgtec.com>,
        Aleksandar Markovic <aleksandar.markovic@imgtec.com>,
        Douglas Leung <douglas.leung@imgtec.com>,
        James Hogan <james.hogan@imgtec.com>,
        Paul Burton <paul.burton@imgtec.com>,
        Petar Jovanovic <petar.jovanovic@imgtec.com>,
        Raghu Gandham <raghu.gandham@imgtec.com>,
        "linux-mips@linux-mips.org" <linux-mips@linux-mips.org>,
        Ralf Baechle <ralf@linux-mips.org>,
        Sasha Levin <Alexander.Levin@microsoft.com>
Subject: [PATCH AUTOSEL for 4.9 174/293] MIPS: VDSO: Add implementation of
 clock_gettime() fallback
Thread-Topic: [PATCH AUTOSEL for 4.9 174/293] MIPS: VDSO: Add implementation
 of clock_gettime() fallback
Thread-Index: AQHTz5k4pM0dugySr0yQpi2cLA+z1w==
Date:   Mon, 9 Apr 2018 00:25:10 +0000
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From: Goran Ferenc <goran.ferenc@imgtec.com>

[ Upstream commit 180902e08f051f72c89ffa366f4e4f7a8e9c753e ]

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>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
---
 arch/mips/vdso/gettimeofday.c | 25 ++++++++++++++++++++++---
 1 file changed, 22 insertions(+), 3 deletions(-)

diff --git a/arch/mips/vdso/gettimeofday.c b/arch/mips/vdso/gettimeofday.c
index fd7d433970bf..5f6337545ee2 100644
--- a/arch/mips/vdso/gettimeofday.c
+++ b/arch/mips/vdso/gettimeofday.c
@@ -20,6 +20,24 @@
 #include <asm/unistd.h>
 #include <asm/vdso.h>
=20
+static __always_inline long clock_gettime_fallback(clockid_t _clkid,
+					   struct timespec *_ts)
+{
+	register struct timespec *ts asm("a1") =3D _ts;
+	register clockid_t clkid asm("a0") =3D _clkid;
+	register long ret asm("v0");
+	register long nr asm("v0") =3D __NR_clock_gettime;
+	register long error asm("a3");
+
+	asm volatile(
+	"       syscall\n"
+	: "=3Dr" (ret), "=3Dr" (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 time=
zone *tz)
 int __vdso_clock_gettime(clockid_t clkid, struct timespec *ts)
 {
 	const union mips_vdso_data *data =3D get_vdso_data();
-	int ret;
+	int ret =3D -1;
=20
 	switch (clkid) {
 	case CLOCK_REALTIME_COARSE:
@@ -223,10 +241,11 @@ int __vdso_clock_gettime(clockid_t clkid, struct time=
spec *ts)
 		ret =3D do_monotonic(ts, data);
 		break;
 	default:
-		ret =3D -ENOSYS;
 		break;
 	}
=20
-	/* If we return -ENOSYS libc should fall back to a syscall. */
+	if (ret)
+		ret =3D clock_gettime_fallback(clkid, ts);
+
 	return ret;
 }
--=20
2.15.1