linux-toradex.git/drivers/clocksource/arm_arch_timer.c, branch v6.0-rc7

clocksource/drivers/arm_arch_timer: Use event stream scaling when available

2022-03-07T17:27:22+00:00

With FEAT_ECV and the 1GHz counter, it is pretty likely that the
event stream divider doesn't fit in the field that holds the
divider value (we only have 4 bits to describe counter bits [15:0]

Thankfully, FEAT_ECV also provides a scaling mechanism to switch
the field to cover counter bits [23:8] instead.

Enable this on arm64 when ECV is available (32bit doesn't have
any detection infrastructure and is unlikely to be run on an
ARMv8.6 system anyway).

Signed-off-by: Marc Zyngier 
Cc: Mark Rutland 
Cc: Daniel Lezcano 
Acked-by: Mark Rutland 
Link: https://lore.kernel.org/r/20220203170502.2694422-1-maz@kernel.org
Signed-off-by: Daniel Lezcano

clocksource/drivers/arm_arch_timer: Force inlining of erratum_set_next_event_generic()

2021-12-10T16:47:00+00:00

With some specific kernel configuration and Clang, the kernel fails
to like with something like:

ld.lld: error: undefined symbol: __compiletime_assert_200
>>> referenced by arch_timer.h:156 (./arch/arm64/include/asm/arch_timer.h:156)
>>>               clocksource/arm_arch_timer.o:(erratum_set_next_event_generic) in archive drivers/built-in.a

ld.lld: error: undefined symbol: __compiletime_assert_197
>>> referenced by arch_timer.h:133 (./arch/arm64/include/asm/arch_timer.h:133)
>>>               clocksource/arm_arch_timer.o:(erratum_set_next_event_generic) in archive drivers/built-in.a
make: *** [Makefile:1161: vmlinux] Error 1

These are due to the BUILD_BUG() macros contained in the low-level
accessors (arch_timer_reg_{write,read}_cp15) being emitted, as the
access type wasn't known at compile time.

Fix this by making erratum_set_next_event_generic() __force_inline,
resulting in the 'access' parameter to be resolved at compile time,
similarly to what is already done for set_next_event().

Fixes: 4775bc63f880 ("Add build-time guards for unhandled register accesses")
Reported-by: Greg Kroah-Hartman 
Signed-off-by: Marc Zyngier 
Cc: Mark Rutland 
Cc: Daniel Lezcano 
Cc: Sami Tolvanen 
Cc: Nick Desaulniers 
Tested-by: Sami Tolvanen 
Reviewed-by: Nathan Chancellor 
Tested-by: Nathan Chancellor 
Link: https://lore.kernel.org/r/20211117113532.3895208-1-maz@kernel.org
Signed-off-by: Daniel Lezcano

clocksource/drivers/arm_arch_timer: Fix masking for high freq counters

2021-10-18T07:20:02+00:00

Unfortunately, the architecture provides no means to determine the bit
width of the system counter. However, we do know the following from the
specification:

 - the system counter is at least 56 bits wide
 - Roll-over time of not less than 40 years

To date, the arch timer driver has depended on the first property,
assuming any system counter to be 56 bits wide and masking off the rest.
However, combining a narrow clocksource mask with a high frequency
counter could result in prematurely wrapping the system counter by a
significant margin. For example, a 56 bit wide, 1GHz system counter
would wrap in a mere 2.28 years!

This is a problem for two reasons: v8.6+ implementations are required to
provide a 64 bit, 1GHz system counter. Furthermore, before v8.6,
implementers may select a counter frequency of their choosing.

Fix the issue by deriving a valid clock mask based on the second
property from above. Set the floor at 56 bits, since we know no system
counter is narrower than that.

[maz: fixed width computation not to lose the last bit, added
      max delta generation for the timer]

Suggested-by: Marc Zyngier 
Signed-off-by: Oliver Upton 
Reviewed-by: Linus Walleij 
Signed-off-by: Marc Zyngier 
Link: https://lore.kernel.org/r/20210807191428.3488948-1-oupton@google.com
Link: https://lore.kernel.org/r/20211017124225.3018098-13-maz@kernel.org
Signed-off-by: Daniel Lezcano

clocksource/drivers/arm_arch_timer: Remove any trace of the TVAL programming interface

2021-10-17T19:47:39+00:00

TVAL usage is now long gone, get rid of the leftovers.

Signed-off-by: Marc Zyngier 
Link: https://lore.kernel.org/r/20211017124225.3018098-11-maz@kernel.org
Signed-off-by: Daniel Lezcano

clocksource/drivers/arm_arch_timer: Work around broken CVAL implementations

2021-10-17T19:47:31+00:00

The Applied Micro XGene-1 SoC has a busted implementation of the
CVAL register: it looks like it is based on TVAL instead of the
other way around. The net effect of this implementation blunder
is that the maximum deadline you can program in the timer is
32bit wide.

Use a MIDR check to notice the broken CPU, and reduce the width
of the timer to 32bit.

Signed-off-by: Marc Zyngier 
Link: https://lore.kernel.org/r/20211017124225.3018098-10-maz@kernel.org
Signed-off-by: Daniel Lezcano

clocksource/drivers/arm_arch_timer: Advertise 56bit timer to the core code

2021-10-17T19:47:27+00:00

Proudly tell the code code that we have a timer able to handle
56 bits deltas.

Signed-off-by: Marc Zyngier 
Link: https://lore.kernel.org/r/20211017124225.3018098-9-maz@kernel.org
Signed-off-by: Daniel Lezcano

clocksource/drivers/arm_arch_timer: Move MMIO timer programming over to CVAL

2021-10-17T19:47:21+00:00

Similarily to the sysreg-based timer, move the MMIO over to using
the CVAL registers instead of TVAL. Note that there is no warranty
that the 64bit MMIO access will be atomic, but the timer is always
disabled at the point where we program CVAL.

Signed-off-by: Marc Zyngier 
Link: https://lore.kernel.org/r/20211017124225.3018098-8-maz@kernel.org
Signed-off-by: Daniel Lezcano

clocksource/drivers/arm_arch_timer: Fix MMIO base address vs callback ordering issue

2021-10-17T19:47:15+00:00

The MMIO timer base address gets published after we have registered
the callbacks and the interrupt handler, which is... a bit dangerous.

Fix this by moving the base address publication to the point where
we register the timer, and expose a pointer to the timer structure
itself rather than a naked value.

Reviewed-by: Oliver Upton 
Reviewed-by: Mark Rutland 
Signed-off-by: Marc Zyngier 
Link: https://lore.kernel.org/r/20211017124225.3018098-7-maz@kernel.org
Signed-off-by: Daniel Lezcano

clocksource/drivers/arm_arch_timer: Move drop _tval from erratum function names

2021-10-17T19:47:10+00:00

The '_tval' name in the erratum handling function names doesn't
make much sense anymore (and they were using CVAL the first place).

Drop the _tval tag.

Reviewed-by: Oliver Upton 
Reviewed-by: Mark Rutland 
Tested-by: Mark Rutland 
Signed-off-by: Marc Zyngier 
Link: https://lore.kernel.org/r/20211017124225.3018098-6-maz@kernel.org
Signed-off-by: Daniel Lezcano

clocksource/drivers/arm_arch_timer: Move system register timer programming over to CVAL

2021-10-17T19:47:05+00:00

In order to cope better with high frequency counters, move the
programming of the timers from the countdown timer (TVAL) over
to the comparator (CVAL).

The programming model is slightly different, as we now need to
read the current counter value to have an absolute deadline
instead of a relative one.

There is a small overhead to this change, which we will address
in the following patches.

Reviewed-by: Oliver Upton 
Reviewed-by: Mark Rutland 
Tested-by: Mark Rutland 
Signed-off-by: Marc Zyngier 
Link: https://lore.kernel.org/r/20211017124225.3018098-5-maz@kernel.org
Signed-off-by: Daniel Lezcano