linux-kernel - [PATCH] x86/uv/time: set ->min_delta_ticks and ->max_delta

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Date:   Thu, 30 Mar 2017 22:04:58 +0200
From:   Nicolai Stange <nicstange@...il.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     John Stultz <john.stultz@...aro.org>, linux-kernel@...r.kernel.org,
        Nicolai Stange <nicstange@...il.com>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Mike Travis <travis@....com>,
        Dimitri Sivanich <sivanich@....com>
Subject: [PATCH] x86/uv/time: set ->min_delta_ticks and ->max_delta_ticks

In preparation for making the clockevents core NTP correction aware,
all clockevent device drivers must set ->min_delta_ticks and
->max_delta_ticks rather than ->min_delta_ns and ->max_delta_ns: a
clockevent device's rate is going to change dynamically and thus, the
ratio of ns to ticks ceases to stay invariant.

Currently, the x86's uv rtc clockevent device is initialized as follows:

  clock_event_device_uv.min_delta_ns = NSEC_PER_SEC /
                                 sn_rtc_cycles_per_second;
  clock_event_device_uv.max_delta_ns = clocksource_uv.mask *
                                 (NSEC_PER_SEC / sn_rtc_cycles_per_second);

This translates to a ->min_delta_ticks value of 1 and a ->max_delta_ticks
value of clocksource_uv.mask.

Initialize ->min_delta_ticks and ->max_delta_ticks with these values
respectively.

This patch alone doesn't introduce any change in functionality as the
clockevents core still looks exclusively at the (untouched) ->min_delta_ns
and ->max_delta_ns. As soon as this has changed, a followup patch will
purge the initialization of ->min_delta_ns and ->max_delta_ns from this
driver.

Signed-off-by: Nicolai Stange <nicstange@...il.com>
---

Notes:
    This prerequisite patch is part of a larger effort to feed NTP
    corrections into the clockevent devices' frequencies and thus
    avoiding their notion of time to diverge from the system's
    one. If you're interested, the current state of the whole series
    can be found at [1].
    
    If you haven't got any objections and these prerequisites get
    merged by 4.12 everywhere, I'll proceed with the remainder of
    this series in 4.13.
    
    Applicable to next-20170324 as well as to John' Stultz tree [2].
    
    [1]
      git://nicst.de/linux.git cev-freq-adj.v10.fortglx-4.12-time
      https://nicst.de/git/?p=linux.git;a=shortlog;h=refs/heads/cev-freq-adj.v10.fortglx-4.12-time
    
    [2]
      https://git.linaro.org/people/john.stultz/linux.git fortglx/4.12/time

 arch/x86/platform/uv/uv_time.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/platform/uv/uv_time.c b/arch/x86/platform/uv/uv_time.c
index 2ee7632d4916..b082d71b08ee 100644
--- a/arch/x86/platform/uv/uv_time.c
+++ b/arch/x86/platform/uv/uv_time.c
@@ -390,9 +390,11 @@ static __init int uv_rtc_setup_clock(void)
 
 	clock_event_device_uv.min_delta_ns = NSEC_PER_SEC /
 						sn_rtc_cycles_per_second;
+	clock_event_device_uv.min_delta_ticks = 1;
 
 	clock_event_device_uv.max_delta_ns = clocksource_uv.mask *
 				(NSEC_PER_SEC / sn_rtc_cycles_per_second);
+	clock_event_device_uv.max_delta_ticks = clocksource_uv.mask;
 
 	rc = schedule_on_each_cpu(uv_rtc_register_clockevents);
 	if (rc) {
-- 
2.12.0