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Date: Thu, 25 Nov 2021 06:48:38 +0100
From: Mateusz Jończyk <mat.jonczyk@...pl>
To: Alexandre Belloni <alexandre.belloni@...tlin.com>
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
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?
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
>>
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