diff options
| author | Mateusz Jończyk | 2022-02-25 22:50:09 +0100 |
|---|---|---|
| committer | Alexandre Belloni | 2022-06-24 21:23:50 +0200 |
| commit | d2a632a8a11756197deb1341bbb09c09abaf20ce (patch) | |
| tree | 2ad9fa01cb1caaf271566709dcf8cd795babbd25 | |
| parent | f2906aa863381afb0015a9eb7fefad885d4e5a56 (diff) | |
rtc: mc146818-lib: reduce RTC_UIP polling period
Waiting 1ms every time is not necessary, for example on some AMD boxes
the RTC_UIP bit is documented as being high for around 270 microseconds
in some cases [1], which agreed with experiments on an SB710
southbridge. So 100us seems optimal.
This in preparation for mach_get_cmos_time() refactoring.
The functions mc146818_get_time() and mach_get_cmos_time() in
arch/x86/kernel/rtc.c perform the same function and the code is
duplicated. mach_get_cmos_time() is busy waiting for the RTC_UIP
bit to clear, so make mc146818_get_time() more similar to it by reducing
the polling period.
[1] AMD SB700/710/750 Register Reference Guide, page 307,
https://developer.amd.com/wordpress/media/2012/10/43009_sb7xx_rrg_pub_1.00.pdf
"SB700 A12: The UIP high pulse is 270 μS Typical when SS on SRC
clock is OFF and 100μ min when SRC SS is ON." [sic]
Signed-off-by: Mateusz Jończyk <mat.jonczyk@o2.pl>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: x86@kernel.org
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Cc: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20220225215011.861477-2-mat.jonczyk@o2.pl
| -rw-r--r-- | drivers/rtc/rtc-mc146818-lib.c | 8 |
1 files changed, 4 insertions, 4 deletions
diff --git a/drivers/rtc/rtc-mc146818-lib.c b/drivers/rtc/rtc-mc146818-lib.c index 522449b25921..f1c09f1db044 100644 --- a/drivers/rtc/rtc-mc146818-lib.c +++ b/drivers/rtc/rtc-mc146818-lib.c @@ -21,13 +21,13 @@ bool mc146818_avoid_UIP(void (*callback)(unsigned char seconds, void *param), unsigned long flags; unsigned char seconds; - for (i = 0; i < 10; i++) { + for (i = 0; i < 100; 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. + * every 100 usec for completion. * * Store the second value before checking UIP so a long lasting * NMI which happens to hit after the UIP check cannot make @@ -37,7 +37,7 @@ bool mc146818_avoid_UIP(void (*callback)(unsigned char seconds, void *param), if (CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP) { spin_unlock_irqrestore(&rtc_lock, flags); - mdelay(1); + udelay(100); continue; } @@ -56,7 +56,7 @@ bool mc146818_avoid_UIP(void (*callback)(unsigned char seconds, void *param), */ if (CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP) { spin_unlock_irqrestore(&rtc_lock, flags); - mdelay(1); + udelay(100); continue; } |