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b=nV7PBw924lPvBzqrI/DpQb1r5WYRKGXbBipF/QylDBVVWVk2N5W4vkOtRlhcxuBm8quLJH XhR5wRV5qwpOLsDg== X-Mailman-Original-Authentication-Results: smtp1.osuosl.org; dmarc=pass (p=none dis=none) header.from=linutronix.de X-Mailman-Original-Authentication-Results: smtp1.osuosl.org; dkim=pass (2048-bit key, unprotected) header.d=linutronix.de header.i=@linutronix.de header.a=rsa-sha256 header.s=2020 header.b=cjZIlLaL; dkim=pass header.d=linutronix.de header.i=@linutronix.de header.a=ed25519-sha256 header.s=2020e header.b=nV7PBw92 Subject: Re: [Intel-wired-lan] [PATCH v6 01/11] x86/tsc: Add base clock properties in clocksource structure X-BeenThere: intel-wired-lan@osuosl.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Intel Wired Ethernet Linux Kernel Driver Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: christopher.s.hall@intel.com, subramanian.mohan@intel.com, lakshmi.sowjanya.d@intel.com, linux-doc@vger.kernel.org, netdev@vger.kernel.org, pandith.n@intel.com, x86@kernel.org, eddie.dong@intel.com, linux-sound@vger.kernel.org, alexandre.torgue@foss.st.com, peter.hilber@opensynergy.com, joabreu@synopsys.com, intel-wired-lan@lists.osuosl.org, mcoquelin.stm32@gmail.com, thejesh.reddy.t.r@intel.com, perex@perex.cz, anthony.l.nguyen@intel.com, andriy.shevchenko@linux.intel.com, davem@davemloft.net Errors-To: intel-wired-lan-bounces@osuosl.org Sender: "Intel-wired-lan" On Wed, Apr 10 2024 at 17:18, lakshmi.sowjanya.d@intel.com wrote: > @@ -48,6 +49,7 @@ struct module; > * @archdata: Optional arch-specific data > * @max_cycles: Maximum safe cycle value which won't overflow on > * multiplication > + * @freq_khz: Clocksource frequency in khz. > * @name: Pointer to clocksource name > * @list: List head for registration (internal) > * @rating: Rating value for selection (higher is better) > @@ -70,6 +72,8 @@ struct module; > * validate the clocksource from which the snapshot was > * taken. > * @flags: Flags describing special properties > + * @base: Hardware abstraction for clock on which a clocksource > + * is based > * @enable: Optional function to enable the clocksource > * @disable: Optional function to disable the clocksource > * @suspend: Optional suspend function for the clocksource > @@ -105,12 +109,14 @@ struct clocksource { > struct arch_clocksource_data archdata; > #endif > u64 max_cycles; > + u32 freq_khz; Q: Why is this a bad place to add this member? A: Because it creates a 4 byte hole in the data structure. > const char *name; > struct list_head list; While adding it here fills a 4 byte hole. Hint: pahole -c clocksource kernel/time/clocksource.o would have told you that. > int rating; > enum clocksource_ids id; > enum vdso_clock_mode vdso_clock_mode; > unsigned long flags; > + struct clocksource_base *base; > diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c > index b58dffc58a8f..2542cfefbdee 100644 > --- a/kernel/time/timekeeping.c > +++ b/kernel/time/timekeeping.c > @@ -1193,6 +1193,40 @@ static bool timestamp_in_interval(u64 start, u64 end, u64 ts) > return false; > } > > +static bool convert_clock(u64 *val, u32 numerator, u32 denominator) > +{ > + u64 rem, res; > + > + if (!numerator || !denominator) > + return false; > + > + res = div64_u64_rem(*val, denominator, &rem) * numerator; > + *val = res + div_u64(rem * numerator, denominator); > + return true; > +} > + > +static bool convert_base_to_cs(struct system_counterval_t *scv) > +{ > + struct clocksource *cs = tk_core.timekeeper.tkr_mono.clock; > + struct clocksource_base *base = cs->base; > + u32 num, den; > + > + /* The timestamp was taken from the time keeper clock source */ > + if (cs->id == scv->cs_id) > + return true; > + > + /* Check whether cs_id matches the base clock */ > + if (!base || base->id != scv->cs_id) > + return false; > + > + num = scv->use_nsecs ? cs->freq_khz : base->numerator; > + den = scv->use_nsecs ? USEC_PER_SEC : base->denominator; > + > + convert_clock(&scv->cycles, num, den); Q: Why does this ignore the return value of convert_clock() ? A: Because all drivers will correctly fill in everything. Q: Then why does convert_clock() bother to check and have a return value? A: Because drivers will fail to correctly fill in everything Thanks, tglx