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Message-ID: <YZ9Dz8gU5yZGqUh1@piout.net>
Date: Thu, 25 Nov 2021 09:05:35 +0100
From: Alexandre Belloni <alexandre.belloni@...tlin.com>
To: Mateusz Jończyk <mat.jonczyk@...pl>
Cc: linux-kernel@...r.kernel.org, linux-rtc@...r.kernel.org,
Alessandro Zummo <a.zummo@...ertech.it>
Subject: Re: [PATCH RESEND v3 4/7] rtc-mc146818-lib: refactor
mc146818_get_time
On 25/11/2021 06:48:38+0100, Mateusz Jończyk wrote:
> W dniu 24.11.2021 o 23:41, Alexandre Belloni pisze:
> > On 19/11/2021 21:42:18+0100, Mateusz Jończyk wrote:
> >> Refactor mc146818_get_time() to make use of mc146818_do_avoiding_UIP().
> >>
> >> Signed-off-by: Mateusz Jończyk <mat.jonczyk@...pl>
> >> Cc: Alessandro Zummo <a.zummo@...ertech.it>
> >> Cc: Alexandre Belloni <alexandre.belloni@...tlin.com>
> >>
> >> ---
> >>
> >> drivers/rtc/rtc-mc146818-lib.c | 111 +++++++++++++--------------------
> >> 1 file changed, 43 insertions(+), 68 deletions(-)
> >>
> >> I'm sorry that the diff is quite difficult to read, but I was unable to
> >> fix this easily.
> >>
> >> diff --git a/drivers/rtc/rtc-mc146818-lib.c b/drivers/rtc/rtc-mc146818-lib.c
> >> index 946ad43a512c..f3178244db37 100644
> >> --- a/drivers/rtc/rtc-mc146818-lib.c
> >> +++ b/drivers/rtc/rtc-mc146818-lib.c
> >> @@ -102,50 +102,20 @@ bool mc146818_does_rtc_work(void)
> >> }
> >> EXPORT_SYMBOL_GPL(mc146818_does_rtc_work);
> >>
> >> -unsigned int mc146818_get_time(struct rtc_time *time)
> >> -{
> >> +struct mc146818_get_time_callback_param {
> >> + struct rtc_time *time;
> >> unsigned char ctrl;
> >> - unsigned long flags;
> >> - unsigned int iter_count = 0;
> >> - unsigned char century = 0;
> >> - bool retry;
> >> -
> >> +#ifdef CONFIG_ACPI
> >> + unsigned char century;
> >> +#endif
> >> #ifdef CONFIG_MACH_DECSTATION
> >> unsigned int real_year;
> >> #endif
> >> +};
> >>
> >> -again:
> >> - if (iter_count > 10) {
> >> - pr_err_ratelimited("Unable to read current time from RTC\n");
> >> - memset(time, 0xff, sizeof(*time));
> >> - return 0;
> >> - }
> >> - iter_count++;
> >> -
> >> - spin_lock_irqsave(&rtc_lock, flags);
> >> -
> >> - /*
> >> - * Check whether there is an update in progress during which the
> >> - * readout is unspecified. The maximum update time is ~2ms. Poll
> >> - * every msec for completion.
> >> - *
> >> - * Store the second value before checking UIP so a long lasting NMI
> >> - * which happens to hit after the UIP check cannot make an update
> >> - * cycle invisible.
> >> - */
> >> - time->tm_sec = CMOS_READ(RTC_SECONDS);
> >> -
> >> - if (CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP) {
> >> - spin_unlock_irqrestore(&rtc_lock, flags);
> >> - mdelay(1);
> >> - goto again;
> >> - }
> >> -
> >> - /* Revalidate the above readout */
> >> - if (time->tm_sec != CMOS_READ(RTC_SECONDS)) {
> >> - spin_unlock_irqrestore(&rtc_lock, flags);
> >> - goto again;
> >> - }
> >> +static void mc146818_get_time_callback(unsigned char seconds, void *param_in)
> >> +{
> >> + struct mc146818_get_time_callback_param *p = param_in;
> >>
> >> /*
> >> * Only the values that we read from the RTC are set. We leave
> >> @@ -153,39 +123,40 @@ unsigned int mc146818_get_time(struct rtc_time *time)
> >> * RTC has RTC_DAY_OF_WEEK, we ignore it, as it is only updated
> >> * by the RTC when initially set to a non-zero value.
> >> */
> >> - time->tm_min = CMOS_READ(RTC_MINUTES);
> >> - time->tm_hour = CMOS_READ(RTC_HOURS);
> >> - time->tm_mday = CMOS_READ(RTC_DAY_OF_MONTH);
> >> - time->tm_mon = CMOS_READ(RTC_MONTH);
> >> - time->tm_year = CMOS_READ(RTC_YEAR);
> >> + p->time->tm_sec = seconds;
> >> + p->time->tm_min = CMOS_READ(RTC_MINUTES);
> >> + p->time->tm_hour = CMOS_READ(RTC_HOURS);
> >> + p->time->tm_mday = CMOS_READ(RTC_DAY_OF_MONTH);
> >> + p->time->tm_mon = CMOS_READ(RTC_MONTH);
> >> + p->time->tm_year = CMOS_READ(RTC_YEAR);
> >> #ifdef CONFIG_MACH_DECSTATION
> >> - real_year = CMOS_READ(RTC_DEC_YEAR);
> >> + p->real_year = CMOS_READ(RTC_DEC_YEAR);
> >> #endif
> >> #ifdef CONFIG_ACPI
> >> if (acpi_gbl_FADT.header.revision >= FADT2_REVISION_ID &&
> >> - acpi_gbl_FADT.century)
> >> - century = CMOS_READ(acpi_gbl_FADT.century);
> >> + acpi_gbl_FADT.century) {
> >> + p->century = CMOS_READ(acpi_gbl_FADT.century);
> >> + } else {
> >> + p->century = 0;
> >> + }
> >> #endif
> >> - ctrl = CMOS_READ(RTC_CONTROL);
> >> - /*
> >> - * Check for the UIP bit again. If it is set now then
> >> - * the above values may contain garbage.
> >> - */
> >> - retry = CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP;
> >> - /*
> >> - * A NMI might have interrupted the above sequence so check whether
> >> - * the seconds value has changed which indicates that the NMI took
> >> - * longer than the UIP bit was set. Unlikely, but possible and
> >> - * there is also virt...
> >> - */
> >> - retry |= time->tm_sec != CMOS_READ(RTC_SECONDS);
> >>
> >> - spin_unlock_irqrestore(&rtc_lock, flags);
> >> + p->ctrl = CMOS_READ(RTC_CONTROL);
> >> +}
> >>
> >> - if (retry)
> >> - goto again;
> >> +unsigned int mc146818_get_time(struct rtc_time *time)
> >> +{
> >> + struct mc146818_get_time_callback_param p = {
> >> + .time = time
> >> + };
> >>
> >> - if (!(ctrl & RTC_DM_BINARY) || RTC_ALWAYS_BCD)
> >> + if (!mc146818_do_avoiding_UIP(mc146818_get_time_callback, &p)) {
> >> + pr_err_ratelimited("Unable to read current time from RTC\n");
> >> + memset(time, 0xff, sizeof(*time));
> >> + return 0;
> >> + }
> >> +
> >> + if (!(p.ctrl & RTC_DM_BINARY) || RTC_ALWAYS_BCD)
> >> {
> >> time->tm_sec = bcd2bin(time->tm_sec);
> >> time->tm_min = bcd2bin(time->tm_min);
> >> @@ -193,15 +164,19 @@ unsigned int mc146818_get_time(struct rtc_time *time)
> >> time->tm_mday = bcd2bin(time->tm_mday);
> >> time->tm_mon = bcd2bin(time->tm_mon);
> >> time->tm_year = bcd2bin(time->tm_year);
> >> - century = bcd2bin(century);
> >> +#ifdef CONFIG_ACPI
> >> + p.century = bcd2bin(p.century);
> >> +#endif
> >> }
> >>
> >> #ifdef CONFIG_MACH_DECSTATION
> >> - time->tm_year += real_year - 72;
> >> + time->tm_year += p.real_year - 72;
> >> #endif
> >>
> >> - if (century > 20)
> >> - time->tm_year += (century - 19) * 100;
> >> +#ifdef CONFIG_ACPI
> > This is an unrelated change
>
> Well, now, when CONFIG_ACPI is not defined, p.century does not exist, so this #ifdef
> is required. I could unconditionally define "century" in mc146818_get_time_callback_param and set
> it manually to 0 when CONFIG_ACPI is not defined. I thought that this approach is more difficult
> to analyse, so did not use it. Should I do this?
>
No, that's fine, thanks!
> Previously, when CONFIG_ACPI was not defined, century was always 0, so
> this doesn't change behaviour.
>
> Greetings,
>
> Mateusz
>
> >> + if (p.century > 20)
> >> + time->tm_year += (p.century - 19) * 100;
> >> +#endif
> >>
> >> /*
> >> * Account for differences between how the RTC uses the values
> >> --
> >> 2.25.1
> >>
>
--
Alexandre Belloni, co-owner and COO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com
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