linux/drivers/clocksource/mips-gic-timer.c

232 lines
5.4 KiB

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>
2015-10-21 09:57:44 +01:00
clocksource/drivers/mips-gic-timer: Make gic_clocksource_of_init() return int In commit: d8152bf85d2c0 ("clocksource/drivers/mips-gic-timer: Convert init function to return error") several return values were added to a void function resulting in the following warnings: clocksource/mips-gic-timer.c: In function 'gic_clocksource_of_init': clocksource/mips-gic-timer.c:175:3: warning: 'return' with a value, in function returning void [enabled by default] clocksource/mips-gic-timer.c:183:4: warning: 'return' with a value, in function returning void [enabled by default] clocksource/mips-gic-timer.c:190:3: warning: 'return' with a value, in function returning void [enabled by default] clocksource/mips-gic-timer.c:195:3: warning: 'return' with a value, in function returning void [enabled by default] clocksource/mips-gic-timer.c:200:3: warning: 'return' with a value, in function returning void [enabled by default] clocksource/mips-gic-timer.c:211:2: warning: 'return' with a value, in function returning void [enabled by default] clocksource/mips-gic-timer.c: At top level: clocksource/mips-gic-timer.c:213:1: warning: comparison of distinct pointer types lacks a cast [enabled by default] clocksource/mips-gic-timer.c: In function 'gic_clocksource_of_init': clocksource/mips-gic-timer.c:183:18: warning: ignoring return value of 'PTR_ERR', declared with attribute warn_unused_result [-Wunused-result] Given that the addition of the return values was intentional, it seems that the conversion of the containing function from void to int was simply overlooked. Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com> Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: linux-mips@linux-mips.org Fixes: d8152bf85d2c ("clocksource/drivers/mips-gic-timer: Convert init function to return error") Link: http://lkml.kernel.org/r/1471429296-9053-3-git-send-email-daniel.lezcano@linaro.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
2016-08-17 12:21:35 +02:00