linux-kernel - [RFC PATCH v4 08/11] lib: vdso: allow fixed clock mode

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Message-Id: <1b278bc1f6859d4df734fb2cde61cf298e6e07fd.1579196675.git.christophe.leroy@c-s.fr>
Date:   Thu, 16 Jan 2020 17:58:32 +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: [RFC PATCH v4 08/11] lib: vdso: allow fixed clock mode

On arches like POWERPC, the clock is always the timebase, it
cannot be changed on the fly and it is always VDSO capable.

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

Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
---
 lib/vdso/gettimeofday.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/lib/vdso/gettimeofday.c b/lib/vdso/gettimeofday.c
index 9fa249809399..724b45c3e8ac 100644
--- a/lib/vdso/gettimeofday.c
+++ b/lib/vdso/gettimeofday.c
@@ -46,6 +46,13 @@ static inline bool __arch_vdso_hres_capable(void)
 }
 #endif
 
+#ifndef __arch_vdso_capable
+static inline bool __arch_vdso_capable(const struct vdso_data *vd)
+{
+	return vd->clock_mode != VDSO_CLOCKMODE_NONE;
+}
+#endif
+
 #ifdef CONFIG_TIME_NS
 static int do_hres_timens(const struct vdso_data *vdns, clockid_t clk,
 			  struct __kernel_timespec *ts)
@@ -66,7 +73,7 @@ static int do_hres_timens(const struct vdso_data *vdns, clockid_t clk,
 	do {
 		seq = vdso_read_begin(vd);
 
-		if (unlikely(vd->clock_mode == VDSO_CLOCKMODE_NONE))
+		if (unlikely(!__arch_vdso_capable(vd)))
 			return -1;
 
 		cycles = __arch_get_hw_counter(vd->clock_mode);
@@ -134,7 +141,7 @@ static __always_inline int do_hres(const struct vdso_data *vd, clockid_t clk,
 		}
 		smp_rmb();
 
-		if (unlikely(vd->clock_mode == VDSO_CLOCKMODE_NONE))
+		if (unlikely(!__arch_vdso_capable(vd)))
 			return -1;
 
 		cycles = __arch_get_hw_counter(vd->clock_mode);
-- 
2.13.3