On 19/11/2021 21:42:17+0100, Mateusz Jończyk wrote:
> Function mc146818_get_time() contains an elaborate mechanism of reading
> the RTC time while no RTC update is in progress. It turns out that
> reading the RTC alarm clock also requires avoiding the RTC update (see
> following patches). Therefore, the mechanism in mc146818_get_time()
> should be reused - so extract it into a separate function.
>
> The logic in mc146818_do_avoiding_UIP() is same as in
> mc146818_get_time() except that after every
>
> if (CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP) {
>
> there is now "mdelay(1)".
>
> To avoid producing an unreadable diff, mc146818_get_time() will be
> refactored to use mc146818_do_avoiding_UIP() in the next patch.
>
> Signed-off-by: Mateusz Jończyk <mat.jonczyk@xxxxx>
> Cc: Alessandro Zummo <a.zummo@xxxxxxxxxxxx>
> Cc: Alexandre Belloni <alexandre.belloni@xxxxxxxxxxx>
>
> ---
> drivers/rtc/rtc-mc146818-lib.c | 69 ++++++++++++++++++++++++++++++++++
> include/linux/mc146818rtc.h | 3 ++
> 2 files changed, 72 insertions(+)
>
> diff --git a/drivers/rtc/rtc-mc146818-lib.c b/drivers/rtc/rtc-mc146818-lib.c
> index b50612ce1a6d..946ad43a512c 100644
> --- a/drivers/rtc/rtc-mc146818-lib.c
> +++ b/drivers/rtc/rtc-mc146818-lib.c
> @@ -8,6 +8,75 @@
> #include <linux/acpi.h>
> #endif
>
> +/*
> + * Execute a function while the UIP (Update-in-progress) bit of the RTC is
> + * unset.
> + *
> + * Warning: callback may be executed more then once.
> + */
> +bool mc146818_do_avoiding_UIP(mc146818_callback_t callback, void *param)
mc146818_avoid_UIP would be a simpler name. Also, I'm pretty sure we can
avoid the mc146818_callback_t typedef
> +{
> + int i;
> + unsigned long flags;
> + unsigned char seconds;
> +
> + for (i = 0; i < 10; i++) {
> + 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.
> + */
> + seconds = CMOS_READ(RTC_SECONDS);
> +
> + if (CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP) {
> + spin_unlock_irqrestore(&rtc_lock, flags);
> + mdelay(1);
> + continue;
> + }
> +
> + /* Revalidate the above readout */
> + if (seconds != CMOS_READ(RTC_SECONDS)) {
> + spin_unlock_irqrestore(&rtc_lock, flags);
> + continue;
> + }
> +
> + if (callback)
> + callback(seconds, param);
> +
> + /*
> + * Check for the UIP bit again. If it is set now then
> + * the above values may contain garbage.
> + */
> + if (CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP) {
> + spin_unlock_irqrestore(&rtc_lock, flags);
> + mdelay(1);
> + continue;
> + }
> +
> + /*
> + * 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...
> + */
> + if (seconds != CMOS_READ(RTC_SECONDS)) {
> + spin_unlock_irqrestore(&rtc_lock, flags);
> + continue;
> + }
> + spin_unlock_irqrestore(&rtc_lock, flags);
> +
> + return true;
> + }
> + return false;
> +}
> +EXPORT_SYMBOL_GPL(mc146818_do_avoiding_UIP);
> +
> /*
> * If the UIP (Update-in-progress) bit of the RTC is set for more then
> * 10ms, the RTC is apparently broken or not present.
> diff --git a/include/linux/mc146818rtc.h b/include/linux/mc146818rtc.h
> index 69c80c4325bf..c0cea97461a0 100644
> --- a/include/linux/mc146818rtc.h
> +++ b/include/linux/mc146818rtc.h
> @@ -127,4 +127,7 @@ bool mc146818_does_rtc_work(void);
> unsigned int mc146818_get_time(struct rtc_time *time);
> int mc146818_set_time(struct rtc_time *time);
>
> +typedef void (*mc146818_callback_t)(unsigned char seconds, void *param);
> +bool mc146818_do_avoiding_UIP(mc146818_callback_t callback, void *param);
> +
> #endif /* _MC146818RTC_H */
> --
> 2.25.1
>
--
Alexandre Belloni, co-owner and COO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com
