path: root/drivers/clocksource/mips-gic-timer.c
diff options
authorAlex Smith <alex.smith@imgtec.com>2015-10-21 09:57:44 +0100
committerRalf Baechle <ralf@linux-mips.org>2015-11-11 08:36:41 +0100
commita7f4df4e21dd8a8dab96e88acd2c9c5017b83fc6 (patch)
tree36c00d0b92be2e2a39da15839f4bfe09be72b572 /drivers/clocksource/mips-gic-timer.c
parentc0a9f72c156baf1e88c33c6ba4450647af1b8804 (diff)
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>
Diffstat (limited to 'drivers/clocksource/mips-gic-timer.c')
1 files changed, 4 insertions, 3 deletions
diff --git a/drivers/clocksource/mips-gic-timer.c b/drivers/clocksource/mips-gic-timer.c
index 02a1945e5093..89d3e4d7900c 100644
--- a/drivers/clocksource/mips-gic-timer.c
+++ b/drivers/clocksource/mips-gic-timer.c
@@ -140,9 +140,10 @@ static cycle_t gic_hpt_read(struct clocksource *cs)
static struct clocksource gic_clocksource = {
- .name = "GIC",
- .read = gic_hpt_read,
+ .name = "GIC",
+ .read = gic_hpt_read,
+ .archdata = { .vdso_clock_mode = VDSO_CLOCK_GIC },
static void __init __gic_clocksource_init(void)