linux/arch/mips/vdso/gettimeofday.c
Alex Smith a7f4df4e21 MIPS: VDSO: Add implementations of gettimeofday() and clock_gettime()
Add user-mode implementations of gettimeofday() and clock_gettime() to
the VDSO. This is currently usable with 2 clocksources: the CP0 count
register, which is accessible to user-mode via RDHWR on R2 and later
cores, or the MIPS Global Interrupt Controller (GIC) timer, which
provides a "user-mode visible" section containing a mirror of its
counter registers. This section must be mapped into user memory, which
is done below the VDSO data page.

When a supported clocksource is not in use, the VDSO functions will
return -ENOSYS, which causes libc to fall back on the standard syscall
path.

When support for neither of these clocksources is compiled into the
kernel at all, the VDSO still provides clock_gettime(), as the coarse
realtime/monotonic clocks can still be implemented. However,
gettimeofday() is not provided in this case as nothing can be done
without a suitable clocksource. This causes the symbol lookup to fail
in libc and it will then always use the standard syscall path.

This patch includes a workaround for a bug in QEMU which results in
RDHWR on the CP0 count register always returning a constant (incorrect)
value. A fix for this has been submitted, and the workaround can be
removed after the fix has been in stable releases for a reasonable
amount of time.

A simple performance test which calls gettimeofday() 1000 times in a
loop and calculates the average execution time gives the following
results on a Malta + I6400 (running at 20MHz):

 - Syscall:    ~31000 ns
 - VDSO (GIC): ~15000 ns
 - VDSO (CP0): ~9500 ns

[markos.chandras@imgtec.com:
- Minor code re-arrangements in order for mappings to be made
in the order they appear to the process' address space.
- Move do_{monotonic, realtime} outside of the MIPS_CLOCK_VSYSCALL ifdef
- Use gic_get_usm_range so we can do the GIC mapping in the
arch/mips/kernel/vdso instead of the GIC irqchip driver]

Signed-off-by: Alex Smith <alex.smith@imgtec.com>
Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>
Cc: linux-kernel@vger.kernel.org
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/11338/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
2015-11-11 08:36:41 +01:00

233 lines
4.7 KiB
C

/*
* Copyright (C) 2015 Imagination Technologies
* Author: Alex Smith <alex.smith@imgtec.com>
*
* This program is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License as published by the
* Free Software Foundation; either version 2 of the License, or (at your
* option) any later version.
*/
#include "vdso.h"
#include <linux/compiler.h>
#include <linux/irqchip/mips-gic.h>
#include <linux/time.h>
#include <asm/clocksource.h>
#include <asm/io.h>
#include <asm/mips-cm.h>
#include <asm/unistd.h>
#include <asm/vdso.h>
static __always_inline int do_realtime_coarse(struct timespec *ts,
const union mips_vdso_data *data)
{
u32 start_seq;
do {
start_seq = vdso_data_read_begin(data);
ts->tv_sec = data->xtime_sec;
ts->tv_nsec = data->xtime_nsec >> data->cs_shift;
} while (vdso_data_read_retry(data, start_seq));
return 0;
}
static __always_inline int do_monotonic_coarse(struct timespec *ts,
const union mips_vdso_data *data)
{
u32 start_seq;
u32 to_mono_sec;
u32 to_mono_nsec;
do {
start_seq = vdso_data_read_begin(data);
ts->tv_sec = data->xtime_sec;
ts->tv_nsec = data->xtime_nsec >> data->cs_shift;
to_mono_sec = data->wall_to_mono_sec;
to_mono_nsec = data->wall_to_mono_nsec;
} while (vdso_data_read_retry(data, start_seq));
ts->tv_sec += to_mono_sec;
timespec_add_ns(ts, to_mono_nsec);
return 0;
}
#ifdef CONFIG_CSRC_R4K
static __always_inline u64 read_r4k_count(void)
{
unsigned int count;
__asm__ __volatile__(
" .set push\n"
" .set mips32r2\n"
" rdhwr %0, $2\n"
" .set pop\n"
: "=r" (count));
return count;
}
#endif
#ifdef CONFIG_CLKSRC_MIPS_GIC
static __always_inline u64 read_gic_count(const union mips_vdso_data *data)
{
void __iomem *gic = get_gic(data);
u32 hi, hi2, lo;
do {
hi = __raw_readl(gic + GIC_UMV_SH_COUNTER_63_32_OFS);
lo = __raw_readl(gic + GIC_UMV_SH_COUNTER_31_00_OFS);
hi2 = __raw_readl(gic + GIC_UMV_SH_COUNTER_63_32_OFS);
} while (hi2 != hi);
return (((u64)hi) << 32) + lo;
}
#endif
static __always_inline u64 get_ns(const union mips_vdso_data *data)
{
u64 cycle_now, delta, nsec;
switch (data->clock_mode) {
#ifdef CONFIG_CSRC_R4K
case VDSO_CLOCK_R4K:
cycle_now = read_r4k_count();
break;
#endif
#ifdef CONFIG_CLKSRC_MIPS_GIC
case VDSO_CLOCK_GIC:
cycle_now = read_gic_count(data);
break;
#endif
default:
return 0;
}
delta = (cycle_now - data->cs_cycle_last) & data->cs_mask;
nsec = (delta * data->cs_mult) + data->xtime_nsec;
nsec >>= data->cs_shift;
return nsec;
}
static __always_inline int do_realtime(struct timespec *ts,
const union mips_vdso_data *data)
{
u32 start_seq;
u64 ns;
do {
start_seq = vdso_data_read_begin(data);
if (data->clock_mode == VDSO_CLOCK_NONE)
return -ENOSYS;
ts->tv_sec = data->xtime_sec;
ns = get_ns(data);
} while (vdso_data_read_retry(data, start_seq));
ts->tv_nsec = 0;
timespec_add_ns(ts, ns);
return 0;
}
static __always_inline int do_monotonic(struct timespec *ts,
const union mips_vdso_data *data)
{
u32 start_seq;
u64 ns;
u32 to_mono_sec;
u32 to_mono_nsec;
do {
start_seq = vdso_data_read_begin(data);
if (data->clock_mode == VDSO_CLOCK_NONE)
return -ENOSYS;
ts->tv_sec = data->xtime_sec;
ns = get_ns(data);
to_mono_sec = data->wall_to_mono_sec;
to_mono_nsec = data->wall_to_mono_nsec;
} while (vdso_data_read_retry(data, start_seq));
ts->tv_sec += to_mono_sec;
ts->tv_nsec = 0;
timespec_add_ns(ts, ns + to_mono_nsec);
return 0;
}
#ifdef CONFIG_MIPS_CLOCK_VSYSCALL
/*
* This is behind the ifdef so that we don't provide the symbol when there's no
* possibility of there being a usable clocksource, because there's nothing we
* can do without it. When libc fails the symbol lookup it should fall back on
* the standard syscall path.
*/
int __vdso_gettimeofday(struct timeval *tv, struct timezone *tz)
{
const union mips_vdso_data *data = get_vdso_data();
struct timespec ts;
int ret;
ret = do_realtime(&ts, data);
if (ret)
return ret;
if (tv) {
tv->tv_sec = ts.tv_sec;
tv->tv_usec = ts.tv_nsec / 1000;
}
if (tz) {
tz->tz_minuteswest = data->tz_minuteswest;
tz->tz_dsttime = data->tz_dsttime;
}
return 0;
}
#endif /* CONFIG_CLKSRC_MIPS_GIC */
int __vdso_clock_gettime(clockid_t clkid, struct timespec *ts)
{
const union mips_vdso_data *data = get_vdso_data();
int ret;
switch (clkid) {
case CLOCK_REALTIME_COARSE:
ret = do_realtime_coarse(ts, data);
break;
case CLOCK_MONOTONIC_COARSE:
ret = do_monotonic_coarse(ts, data);
break;
case CLOCK_REALTIME:
ret = do_realtime(ts, data);
break;
case CLOCK_MONOTONIC:
ret = do_monotonic(ts, data);
break;
default:
ret = -ENOSYS;
break;
}
/* If we return -ENOSYS libc should fall back to a syscall. */
return ret;
}