[PATCH v4 06/12] arm: vdso: add support for clock_getres

[Mark Salyzyn]

Take an effort to recode the arm64 vdso code from assembler to C
previously submitted by Andrew Pinski <apinski at cavium.com>, 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.

Add clock_getres vdso support to match up with existing support in
the arm64's vdso.

Signed-off-by: Mark Salyzyn <salyzyn at android.com>
Cc: James Morse <james.morse at arm.com>
Cc: Russell King <linux at armlinux.org.uk>
Cc: Catalin Marinas <catalin.marinas at arm.com>
Cc: Will Deacon <will.deacon at arm.com>
Cc: Andy Lutomirski <luto at amacapital.net>
Cc: Dmitry Safonov <dsafonov at virtuozzo.com>
Cc: John Stultz <john.stultz at linaro.org>
Cc: Mark Rutland <mark.rutland at arm.com>
Cc: Laura Abbott <labbott at redhat.com>
Cc: Kees Cook <keescook at chromium.org>
Cc: Ard Biesheuvel <ard.biesheuvel at linaro.org>
Cc: Andy Gross <andy.gross at linaro.org>
Cc: Kevin Brodsky <kevin.brodsky at arm.com>
Cc: Andrew Pinski <apinski at cavium.com>
Cc: Thomas Gleixner <tglx at linutronix.de>
Cc: linux-kernel at vger.kernel.org
Cc: linux-arm-kernel at lists.infradead.org

v2:
- split first CL into 7 of 7 pieces

v4:
- update commit message to reflect overall reasoning.
- replace typeof() with long for nsec
- replace clock_id with clock to match usage elsewhere.

---
 arch/arm/kernel/vdso.c        |  1 +
 arch/arm/vdso/vdso.lds.S      |  1 +
 arch/arm/vdso/vgettimeofday.c | 23 +++++++++++++++++++++++
 3 files changed, 25 insertions(+)

diff --git a/arch/arm/kernel/vdso.c b/arch/arm/kernel/vdso.c
index 7377638a3b00..287424541f3a 100644
--- a/arch/arm/kernel/vdso.c
+++ b/arch/arm/kernel/vdso.c
@@ -189,6 +189,7 @@ static void __init patch_vdso(void *ehdr)
 	if (!cntvct_ok) {
 		vdso_nullpatch_one(&einfo, "__vdso_gettimeofday");
 		vdso_nullpatch_one(&einfo, "__vdso_clock_gettime");
+		vdso_nullpatch_one(&einfo, "__vdso_clock_getres");
 	}
 }
 
diff --git a/arch/arm/vdso/vdso.lds.S b/arch/arm/vdso/vdso.lds.S
index 89ca89f12d23..1d81e8c3acf6 100644
--- a/arch/arm/vdso/vdso.lds.S
+++ b/arch/arm/vdso/vdso.lds.S
@@ -82,6 +82,7 @@ VERSION
 	global:
 		__vdso_clock_gettime;
 		__vdso_gettimeofday;
+		__vdso_clock_getres;
 	local: *;
 	};
 }
diff --git a/arch/arm/vdso/vgettimeofday.c b/arch/arm/vdso/vgettimeofday.c
index 2b9fce92904e..1152308067e1 100644
--- a/arch/arm/vdso/vgettimeofday.c
+++ b/arch/arm/vdso/vgettimeofday.c
@@ -31,6 +31,7 @@
 
 DEFINE_FALLBACK(gettimeofday, struct timeval *, tv, struct timezone *, tz)
 DEFINE_FALLBACK(clock_gettime, clockid_t, clock, struct timespec *, ts)
+DEFINE_FALLBACK(clock_getres, clockid_t, clock, struct timespec *, ts)
 
 static notrace u32 vdso_read_begin(const struct vdso_data *vd)
 {
@@ -296,3 +297,25 @@ notrace int __vdso_gettimeofday(struct timeval *tv, struct timezone *tz)
 
 	return 0;
 }
+
+int __vdso_clock_getres(clockid_t clock, struct timespec *res)
+{
+	long nsec;
+
+	if (clock == CLOCK_REALTIME ||
+	    clock == CLOCK_MONOTONIC ||
+	    clock == CLOCK_MONOTONIC_RAW)
+		nsec = MONOTONIC_RES_NSEC;
+	else if (clock == CLOCK_REALTIME_COARSE ||
+		 clock == CLOCK_MONOTONIC_COARSE)
+		nsec = LOW_RES_NSEC;
+	else
+		return clock_getres_fallback(clock, res);
+
+	if (likely(res != NULL)) {
+		res->tv_sec = 0;
+		res->tv_nsec = nsec;
+	}
+
+	return 0;
+}
-- 
2.15.0.rc2.357.g7e34df9404-goog