linux-kernel - [PATCH v5 4/6] lib/vdso: Allow fixed clock mode

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Date:   Thu, 30 Jan 2020 16:08:38 +0000 (UTC)
From:   Christophe Leroy <christophe.leroy@....fr>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>, nathanl@...ux.ibm.com,
        arnd@...db.de, tglx@...utronix.de, vincenzo.frascino@....com,
        luto@...nel.org
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-arm-kernel@...ts.infradead.org, linux-mips@...r.kernel.org,
        x86@...nel.org
Subject: [PATCH v5 4/6] lib/vdso: Allow fixed clock mode

Some architectures have a fixed clocksource which is known at compile
time and cannot be replaced or disabled at runtime, e.g. timebase on
PowerPC. For such cases the clock mode check in the VDSO code is
pointless.

Therefore, give architectures the opportunity to redefine the way
clock_mode is checked by moving the check into an
__arch_vdso_capable() macro.

Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
---
 lib/vdso/gettimeofday.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/lib/vdso/gettimeofday.c b/lib/vdso/gettimeofday.c
index 72d65dd50cb4..0b4b71880f22 100644
--- a/lib/vdso/gettimeofday.c
+++ b/lib/vdso/gettimeofday.c
@@ -120,12 +120,18 @@ static __always_inline int do_hres(const struct vdso_data *vd, clockid_t clk,
 			cpu_relax();
 		}
 		smp_rmb();
+#ifdef __arch_vdso_capable
+		if (unlikely(!__arch_vdso_capable(vd->clock_mode)))
+			return -1;
+#endif
 
 		cycles = __arch_get_hw_counter(vd->clock_mode);
 		ns = vdso_ts->nsec;
 		last = vd->cycle_last;
+#ifndef __arch_vdso_capable
 		if (unlikely((s64)cycles < 0))
 			return -1;
+#endif
 
 		ns += vdso_calc_delta(cycles, last, vd->mask, vd->mult);
 		ns >>= vd->shift;
-- 
2.25.0