linux/drivers/clocksource
Doug Anderson 65b5732d24 clocksource: arch_timer: Allow the device tree to specify uninitialized timer registers
Some 32-bit (ARMv7) systems are architected like this:

* The firmware doesn't know and doesn't care about hypervisor mode and
  we don't want to add the complexity of hypervisor there.

* The firmware isn't involved in SMP bringup or resume.

* The ARCH timer come up with an uninitialized offset (CNTVOFF)
  between the virtual and physical counters.  Each core gets a
  different random offset.

* The device boots in "Secure SVC" mode.

* Nothing has touched the reset value of CNTHCTL.PL1PCEN or
  CNTHCTL.PL1PCTEN (both default to 1 at reset)

On systems like the above, it doesn't make sense to use the virtual
counter.  There's nobody managing the offset and each time a core goes
down and comes back up it will get reinitialized to some other random
value.

This adds an optional property which can inform the kernel of this
situation, and firmware is free to remove the property if it is going
to initialize the CNTVOFF registers when each CPU comes out of reset.

Currently, the best course of action in this case is to use the
physical timer, which is why it is important that CNTHCTL hasn't been
changed from its reset value and it's a reasonable assumption given
that the firmware has never entered HYP mode.

Note that it's been said that on ARMv8 systems the firmware and
kernel really can't be architected as described above.  That means
using the physical timer like this really only makes sense for ARMv7
systems.

Signed-off-by: Doug Anderson <dianders@chromium.org>
Signed-off-by: Sonny Rao <sonnyrao@chromium.org>
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Olof Johansson <olof@lixom.net>
2014-12-04 23:31:55 -08:00
..
acpi_pm.c
arm_arch_timer.c clocksource: arch_timer: Allow the device tree to specify uninitialized timer registers 2014-12-04 23:31:55 -08:00
arm_global_timer.c ARM: make it easier to check the CPU part number correctly 2014-07-18 12:29:02 +01:00
bcm2835_timer.c
bcm_kona_timer.c
cadence_ttc_timer.c clocksource: cadence_ttc: Add support for 32bit mode 2014-09-29 01:59:09 +02:00
clksrc-dbx500-prcmu.c
clksrc-of.c
clps711x-timer.c clocksource: clps711x: Add CLPS711X clocksource driver 2014-07-23 12:02:35 +02:00
cs5535-clockevt.c
dummy_timer.c time: Replace __get_cpu_var uses 2014-08-26 13:45:44 -04:00
dw_apb_timer_of.c
dw_apb_timer.c
em_sti.c
exynos_mct.c clocksource: exynos_mct: Only use 32-bits where possible 2014-07-23 12:02:41 +02:00
fsl_ftm_timer.c
i8253.c
Kconfig Merge branch 'timers-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2014-10-09 06:35:05 -04:00
Makefile Merge branch 'timers-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2014-10-09 06:35:05 -04:00
meson6_timer.c ARM: meson6: clocksource: Add Meson6 timer support 2014-09-29 01:50:05 +02:00
metag_generic.c drivers/clocksource: Replace __get_cpu_var used for address calculation 2014-08-26 13:45:46 -04:00
mmio.c
moxart_timer.c
mtk_timer.c clocksource: Add support for the Mediatek SoCs 2014-07-23 12:02:31 +02:00
mxs_timer.c
nomadik-mtu.c
pxa_timer.c clocksource: pxa: Add device-tree support for PXA timer 2014-07-23 12:02:37 +02:00
qcom-timer.c clocksource: Replace __this_cpu_ptr with raw_cpu_ptr 2014-08-26 13:45:56 -04:00
samsung_pwm_timer.c
scx200_hrt.c
sh_cmt.c clocksource: sh_cmt: Add DT support 2014-07-04 15:46:17 +02:00
sh_mtu2.c clocksource: sh_mtu2: Add DT support 2014-07-04 15:50:29 +02:00
sh_tmu.c clocksource: sh_tmu: Add DT support 2014-07-04 15:50:28 +02:00
sun4i_timer.c
tcb_clksrc.c clocksource: tcb_clksrc: Sanitize IRQ request 2014-09-29 01:50:05 +02:00
tegra20_timer.c clocksource: tegra: Use us counter as delay timer 2014-06-16 12:48:12 -06:00
time-armada-370-xp.c
time-efm32.c
time-orion.c
timer-atmel-pit.c ARM: at91: PIT: Move the driver to drivers/clocksource 2014-09-15 17:55:48 +02:00
timer-keystone.c
timer-marco.c clocksource: sirf: Disable counter before re-setting it 2014-09-29 01:59:24 +02:00
timer-prima2.c clocksource: sirf: Fix incorrect clock enable counter for timer 2014-07-23 12:02:34 +02:00
timer-sun5i.c
timer-u300.c
versatile.c clocksource: versatile: Use sched_clock_register() 2014-06-04 07:46:10 -07:00
vf_pit_timer.c clocksource: vf_pit_timer: Support shutdown mode 2014-09-29 01:50:05 +02:00
vt8500_timer.c
zevio-timer.c