Re: [Minios-devel] [UNIKRAFT PATCHv5 25/46] plat/kvm: Add Arm64 virtual timer library to provide ticks

["Wei Chen (Arm Technology China)" <Wei.Chen@xxxxxxx>]

Hi Julien,

> -----Original Message-----
> From: Julien Grall <julien.grall@xxxxxxx>
> Sent: 2018年9月7日 23:25
> To: Wei Chen (Arm Technology China) <Wei.Chen@xxxxxxx>; minios-
> devel@xxxxxxxxxxxxxxxxxxxx; simon.kuenzer@xxxxxxxxx
> Cc: Kaly Xin (Arm Technology China) <Kaly.Xin@xxxxxxx>; nd <nd@xxxxxxx>
> Subject: Re: [Minios-devel] [UNIKRAFT PATCHv5 25/46] plat/kvm: Add Arm64
> virtual timer library to provide ticks
> 
> Hi Wei,
> 
> On 08/10/2018 08:08 AM, Wei Chen wrote:
> > From: Wei Chen <Wei.Chen@xxxxxxx>
> >
> > On KVM platform, print debug message will use ukplat_monotonic_clock
> > to provide timestamp. So we implement this simple virtual timer
> > library for timestamp.
> >
> > Signed-off-by: Wei Chen <Wei.Chen@xxxxxxx>
> > ---
> >   plat/common/arm/time.c | 123 +++++++++++++++++++++++++++++++++++++++++
> >   plat/kvm/Makefile.uk   |   1 +
> >   2 files changed, 124 insertions(+)
> >   create mode 100644 plat/common/arm/time.c
> >
> > diff --git a/plat/common/arm/time.c b/plat/common/arm/time.c
> > new file mode 100644
> > index 0000000..4d955f3
> > --- /dev/null
> > +++ b/plat/common/arm/time.c
> > @@ -0,0 +1,123 @@
> > +/* SPDX-License-Identifier: BSD-3-Clause */
> > +/*
> > + * Authors: Wei Chen <Wei.Chen@xxxxxxx>
> > + *
> > + * Copyright (c) 2018, Arm Ltd. All rights reserved.
> > + *
> > + * Redistribution and use in source and binary forms, with or without
> > + * modification, are permitted provided that the following conditions
> > + * are met:
> > + *
> > + * 1. Redistributions of source code must retain the above copyright
> > + *    notice, this list of conditions and the following disclaimer.
> > + * 2. Redistributions in binary form must reproduce the above copyright
> > + *    notice, this list of conditions and the following disclaimer in the
> > + *    documentation and/or other materials provided with the distribution.
> > + * 3. Neither the name of the copyright holder nor the names of its
> > + *    contributors may be used to endorse or promote products derived from
> > + *    this software without specific prior written permission.
> > + *
> > + * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
> IS"
> > + * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
> THE
> > + * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
> PURPOSE
> > + * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS
> BE
> > + * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
> > + * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
> > + * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
> > + * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
> > + * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
> > + * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
> THE
> > + * POSSIBILITY OF SUCH DAMAGE.
> > + *
> > + * THIS HEADER MAY NOT BE EXTRACTED OR MODIFIED IN ANY WAY.
> > + */
> > +#include <uk/assert.h>
> > +#include <uk/plat/time.h>
> > +#include <cpu.h>
> > +
> > +static uint64_t boot_ticks;
> > +static uint32_t counter_freq;
> > +
> > +/*
> > + * Shift factor for counter scaling multiplier; referred to as S in the
> > + * following comments.
> > + */
> > +static uint8_t counter_shift;
> > +
> > +/* Multiplier for converting counter ticks to nsecs. (0.S) fixed point. */
> > +static uint32_t ns_per_tick;
> > +
> > +/* How many nanoseconds per second */
> > +#define NSEC_PER_SEC ukarch_time_sec_to_nsec(1)
> > +
> > +static inline uint64_t ticks_to_ns(uint64_t ticks)
> > +{
> > +   return (ns_per_tick * ticks) >> counter_shift;
> > +}
> > +
> > +static inline uint64_t get_counter_frequency(void)
> 
> The frequency is a 32-bit value.

OK.

> 
> > +{
> > +   return SYSREG_READ(cntfrq_el0);
> 
> Also, on a few platforms the frequency is not configured correctly by
> the firmware. A property in the DT (clock-frequency) has been introduced
> to workaround those firmware. I would consider to support it here.

Ok, I will try to get frequency from DT first, if failed then try to get
it from register.

> 
> > +}
> > +
> > +static inline uint64_t read_virtual_count(void)
> > +{
> > +   return SYSREG_READ(cntvct_el0);
> 
> On arm, this register is 64-bit as well. So I would introduce
> SYSREG_READ32 and SYSREG_READ64 to differentiate the size here.
> 
> SYSREG_READ would still be kept around for native size.
> 

Make sense.

> > +}
> > +
> > +/*
> > + * monotonic_clock(): returns # of nanoseconds passed since
> > + * generic_timer_time_init()
> > + */
> > +static __nsec generic_timer_monotonic(void)
> > +{
> > +   return (__nsec)ticks_to_ns(read_virtual_count() - boot_ticks);
> > +}
> > +
> > +/*
> > + * Return epoch offset (wall time offset to monotonic clock start).
> > + */
> > +static __u64  generic_timer_epochoffset(void)
> > +{
> > +   return 0;
> > +} > +
> > +static int generic_timer_init(void)
> > +{
> > +   /*
> > +    * Calculate counter shift factor and scaling multiplier.
> > +    *
> > +    * counter_shift (S) needs to be the largest (<=32) shift factor where
> > +    * the result of the counter_mult calculation below fits into uint32_t
> 
> counter_mult does not exist below.

Ok, I will adjust the comment.

> 
> > +    * without truncation. Note that we disallow an S of zero to ensure
> > +    * the loop always terminates.
> > +    *
> > +    * (0.S) counter_mult = NSEC_PER_SEC (S.S) / counter_freq (S.0)
> > +    */
> > +   uint64_t tmp;
> > +
> > +   counter_freq = get_counter_frequency();
> > +   counter_shift = 32;
> > +   do {
> > +           tmp = (NSEC_PER_SEC << counter_shift) / counter_freq;
> > +           if ((tmp & 0xFFFFFFFF00000000L) == 0L)
> > +                   ns_per_tick = (uint32_t)tmp;
> > +           else
> > +                   counter_shift--;
> > +   } while (counter_shift > 0 && ns_per_tick == 0L);
> > +   UK_BUGON(!ns_per_tick);
> > +
> > +   /*
> > +    * Monotonic time begins at boot_ticks (first read of counter
> > +    * before calibration).
> > +    */
> > +   boot_ticks = read_virtual_count();
> > +
> > +   return 0;
> > +}
> > +
> > +struct ukplat_time_ops arch_timer_ops = {
> > +   .init = generic_timer_init,
> > +   .monotonic = generic_timer_monotonic,
> > +   .epochoffset = generic_timer_epochoffset,
> > +};
> > diff --git a/plat/kvm/Makefile.uk b/plat/kvm/Makefile.uk
> > index efeea31..2dc6db5 100644
> > --- a/plat/kvm/Makefile.uk
> > +++ b/plat/kvm/Makefile.uk
> > @@ -54,6 +54,7 @@ ifeq ($(findstring y,$(CONFIG_KVM_KERNEL_SERIAL_CONSOLE)
> $(CONFIG_KVM_DEBUG_SERI
> >   LIBKVMPLAT_SRCS-$(CONFIG_ARCH_ARM_64) +=
> $(UK_PLAT_COMMON_BASE)/arm/console.c|common
> >   endif
> >   LIBKVMPLAT_SRCS-$(CONFIG_ARCH_ARM_64) +=
> $(UK_PLAT_COMMON_BASE)/arm/cache64.S|common
> > +LIBKVMPLAT_SRCS-$(CONFIG_ARCH_ARM_64) +=
> $(UK_PLAT_COMMON_BASE)/arm/time.c|common
> >   LIBKVMPLAT_SRCS-$(CONFIG_ARCH_ARM_64) += $(LIBKVMPLAT_BASE)/arm/entry64.S
> >   LIBKVMPLAT_SRCS-$(CONFIG_ARCH_ARM_64) += $(LIBKVMPLAT_BASE)/arm/setup.c
> >   endif
> >
> 
> Cheers,
> 
> 
> --
> Julien Grall
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