From: Atish Patra <Atish.Patra@wdc.com>
To: "hch@lst.de" <hch@lst.de>,
"paul.walmsley@sifive.com" <paul.walmsley@sifive.com>,
"palmer@sifive.com" <palmer@sifive.com>
Cc: "linux-riscv@lists.infradead.org" <linux-riscv@lists.infradead.org>
Subject: Re: [PATCH 5/6] riscv: don't use the rdtime(h) pseudo-instructions
Date: Sat, 24 Aug 2019 00:43:20 +0000 [thread overview]
Message-ID: <bcc437eca5ed4196fc6cba5b852bd9d4e858f405.camel@wdc.com> (raw)
In-Reply-To: <d15a578760061a5a0ebad8ca6024768f831686d2.camel@wdc.com>
On Fri, 2019-08-23 at 17:37 -0700, Atish Patra wrote:
> On Wed, 2019-08-21 at 23:58 +0900, Christoph Hellwig wrote:
> > If we just use the CSRs that these map to directly the code is
> > simpler
> > and doesn't require extra inline assembly code. Also fix up the
> > top-
> > level
> > comment in timer-riscv.c to not talk about the cycle count or
> > mention
> > details of the clocksource interface, of which this file is just a
> > consumer.
> >
> > Signed-off-by: Christoph Hellwig <hch@lst.de>
> > ---
> > arch/riscv/include/asm/timex.h | 44 +++++++++++++++------------
> > ----
> > drivers/clocksource/timer-riscv.c | 17 +++---------
> > 2 files changed, 25 insertions(+), 36 deletions(-)
> >
> > diff --git a/arch/riscv/include/asm/timex.h
> > b/arch/riscv/include/asm/timex.h
> > index 6a703ec9d796..c7ef131b9e4c 100644
> > --- a/arch/riscv/include/asm/timex.h
> > +++ b/arch/riscv/include/asm/timex.h
> > @@ -6,43 +6,41 @@
> > #ifndef _ASM_RISCV_TIMEX_H
> > #define _ASM_RISCV_TIMEX_H
> >
> > -#include <asm/param.h>
> > +#include <asm/csr.h>
> >
> > typedef unsigned long cycles_t;
> >
> > -static inline cycles_t get_cycles_inline(void)
> > +static inline cycles_t get_cycles(void)
> > {
> > - cycles_t n;
> > -
> > - __asm__ __volatile__ (
> > - "rdtime %0"
> > - : "=r" (n));
> > - return n;
> > + return csr_read(CSR_TIME);
>
> Does this work correctly in QEMU ? I was looking at the qemu code and
> it looks like it returns cpu_get_host_ticks which seems wrong to me.
>
> https://github.com/qemu/qemu/blob/master/target/riscv/csr.c#L213
>
>
Nevermind. I missed the CONFIG_USER_ONLY and got confused.
csr_read will also trap and get the correct value.
Regards,
Atish
> > }
> > -#define get_cycles get_cycles_inline
> > +#define get_cycles get_cycles
> >
> > #ifdef CONFIG_64BIT
> > -static inline uint64_t get_cycles64(void)
> > +static inline u64 get_cycles64(void)
> > +{
> > + return get_cycles();
> > +}
> > +#else /* CONFIG_64BIT */
> > +static inline u32 get_cycles_hi(void)
> > {
> > - return get_cycles();
> > + return csr_read(CSR_TIMEH);
> > }
> > -#else
> > -static inline uint64_t get_cycles64(void)
> > +
> > +static inline u64 get_cycles64(void)
> > {
> > - u32 lo, hi, tmp;
> > - __asm__ __volatile__ (
> > - "1:\n"
> > - "rdtimeh %0\n"
> > - "rdtime %1\n"
> > - "rdtimeh %2\n"
> > - "bne %0, %2, 1b"
> > - : "=&r" (hi), "=&r" (lo), "=&r" (tmp));
> > + u32 hi, lo;
> > +
> > + do {
> > + hi = get_cycles_hi();
> > + lo = get_cycles();
> > + } while (hi != get_cycles_hi());
> > +
> > return ((u64)hi << 32) | lo;
> > }
> > -#endif
> > +#endif /* CONFIG_64BIT */
> >
> > #define ARCH_HAS_READ_CURRENT_TIMER
> > -
> > static inline int read_current_timer(unsigned long *timer_val)
> > {
> > *timer_val = get_cycles();
> > diff --git a/drivers/clocksource/timer-riscv.c
> > b/drivers/clocksource/timer-riscv.c
> > index 09e031176bc6..470c7ef02ea4 100644
> > --- a/drivers/clocksource/timer-riscv.c
> > +++ b/drivers/clocksource/timer-riscv.c
> > @@ -2,6 +2,10 @@
> > /*
> > * Copyright (C) 2012 Regents of the University of California
> > * Copyright (C) 2017 SiFive
> > + *
> > + * All RISC-V systems have a timer attached to every hart. These
> > timers can be
> > + * read from the "time" and "timeh" CSRs, and can use the SBI to
> > setup
> > + * events.
> > */
> > #include <linux/clocksource.h>
> > #include <linux/clockchips.h>
> > @@ -12,19 +16,6 @@
> > #include <asm/smp.h>
> > #include <asm/sbi.h>
> >
> > -/*
> > - * All RISC-V systems have a timer attached to every hart. These
> > timers can be
> > - * read by the 'rdcycle' pseudo instruction, and can use the SBI
> > to
> > setup
> > - * events. In order to abstract the architecture-specific timer
> > reading and
> > - * setting functions away from the clock event insertion code, we
> > provide
> > - * function pointers to the clockevent subsystem that perform two
> > basic
> > - * operations: rdtime() reads the timer on the current CPU, and
> > - * next_event(delta) sets the next timer event to 'delta' cycles
> > in
> > the future.
> > - * As the timers are inherently a per-cpu resource, these
> > callbacks
> > perform
> > - * operations on the current hart. There is guaranteed to be
> > exactly one timer
> > - * per hart on all RISC-V systems.
> > - */
> > -
> > static int riscv_clock_next_event(unsigned long delta,
> > struct clock_event_device *ce)
> > {
--
Regards,
Atish
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next prev parent reply other threads:[~2019-08-24 0:43 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-21 14:58 misc riscv cleanups Christoph Hellwig
2019-08-21 14:58 ` [PATCH 1/6] riscv: refactor the IPI code Christoph Hellwig
2019-08-24 1:03 ` Atish Patra
2019-09-05 8:44 ` Paul Walmsley
2019-08-21 14:58 ` [PATCH 2/6] riscv: cleanup send_ipi_mask Christoph Hellwig
2019-08-24 0:11 ` Atish Patra
2019-08-26 11:28 ` hch
2019-08-27 18:45 ` Atish Patra
2019-09-05 8:46 ` Paul Walmsley
2019-08-21 14:58 ` [PATCH 3/6] riscv: optimize send_ipi_single Christoph Hellwig
2019-08-24 0:26 ` Atish Patra
2019-08-26 11:29 ` hch
2019-08-27 18:48 ` Atish Patra
2019-09-05 8:48 ` Paul Walmsley
2019-08-21 14:58 ` [PATCH 4/6] riscv: cleanup riscv_cpuid_to_hartid_mask Christoph Hellwig
2019-08-24 0:03 ` Atish Patra
2019-09-05 8:50 ` Paul Walmsley
2019-08-21 14:58 ` [PATCH 5/6] riscv: don't use the rdtime(h) pseudo-instructions Christoph Hellwig
2019-08-24 0:37 ` Atish Patra
2019-08-24 0:43 ` Atish Patra [this message]
2019-08-26 11:30 ` hch
2019-08-27 18:50 ` Atish Patra
2019-09-05 8:55 ` Paul Walmsley
2019-08-21 14:58 ` [PATCH 6/6] riscv: move the TLB flush logic out of line Christoph Hellwig
2019-08-24 0:03 ` Atish Patra
2019-09-05 8:58 ` Paul Walmsley
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