| Message ID | 20220225215011.861477-2-mat.jonczyk@o2.pl |
|---|---|
| State | Superseded |
| Headers | show |
| Series | rtc,x86: RTC CMOS refactoring | expand |
From: Alexandre Belloni <alexandre.belloni@bootlin.com> On Fri, 25 Feb 2022 22:50:09 +0100, Mateusz Jończyk wrote: > 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. > > [...] Applied, thanks! [1/3] rtc-mc146818-lib: reduce RTC_UIP polling period commit: 4b94a798e1ca59f4614f5ff6b94fe0c287412b9b Best regards,
diff --git a/drivers/rtc/rtc-mc146818-lib.c b/drivers/rtc/rtc-mc146818-lib.c index ae9f131b43c0..ae4b19e0a981 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; }
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> --- drivers/rtc/rtc-mc146818-lib.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)