From ea6fa4961aab8f90a8aa03575a98b4bda368d4b6 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Mateusz=20Jo=C5=84czyk?= Date: Fri, 10 Dec 2021 21:01:26 +0100 Subject: rtc: mc146818-lib: fix RTC presence check MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit To prevent an infinite loop in mc146818_get_time(), commit 211e5db19d15 ("rtc: mc146818: Detect and handle broken RTCs") added a check for RTC availability. Together with a later fix, it checked if bit 6 in register 0x0d is cleared. This, however, caused a false negative on a motherboard with an AMD SB710 southbridge; according to the specification [1], bit 6 of register 0x0d of this chipset is a scratchbit. This caused a regression in Linux 5.11 - the RTC was determined broken by the kernel and not used by rtc-cmos.c [3]. This problem was also reported in Fedora [4]. As a better alternative, check whether the UIP ("Update-in-progress") bit is set for longer then 10ms. If that is the case, then apparently the RTC is either absent (and all register reads return 0xff) or broken. Also limit the number of loop iterations in mc146818_get_time() to 10 to prevent an infinite loop there. The functions mc146818_get_time() and mc146818_does_rtc_work() will be refactored later in this patch series, in order to fix a separate problem with reading / setting the RTC alarm time. This is done so to avoid a confusion about what is being fixed when. In a previous approach to this problem, I implemented a check whether the RTC_HOURS register contains a value <= 24. This, however, sometimes did not work correctly on my Intel Kaby Lake laptop. According to Intel's documentation [2], "the time and date RAM locations (0-9) are disconnected from the external bus" during the update cycle so reading this register without checking the UIP bit is incorrect. [1] AMD SB700/710/750 Register Reference Guide, page 308, https://developer.amd.com/wordpress/media/2012/10/43009_sb7xx_rrg_pub_1.00.pdf [2] 7th Generation Intel ® Processor Family I/O for U/Y Platforms [...] Datasheet Volume 1 of 2, page 209 Intel's Document Number: 334658-006, https://www.intel.com/content/dam/www/public/us/en/documents/datasheets/7th-and-8th-gen-core-family-mobile-u-y-processor-lines-i-o-datasheet-vol-1.pdf [3] Functions in arch/x86/kernel/rtc.c apparently were using it. [4] https://bugzilla.redhat.com/show_bug.cgi?id=1936688 Fixes: 211e5db19d15 ("rtc: mc146818: Detect and handle broken RTCs") Fixes: ebb22a059436 ("rtc: mc146818: Dont test for bit 0-5 in Register D") Signed-off-by: Mateusz Jończyk Cc: Thomas Gleixner Cc: Alessandro Zummo Cc: Alexandre Belloni Signed-off-by: Alexandre Belloni Link: https://lore.kernel.org/r/20211210200131.153887-5-mat.jonczyk@o2.pl --- include/linux/mc146818rtc.h | 1 + 1 file changed, 1 insertion(+) (limited to 'include') diff --git a/include/linux/mc146818rtc.h b/include/linux/mc146818rtc.h index 0661af17a758..69c80c4325bf 100644 --- a/include/linux/mc146818rtc.h +++ b/include/linux/mc146818rtc.h @@ -123,6 +123,7 @@ struct cmos_rtc_board_info { #define RTC_IO_EXTENT_USED RTC_IO_EXTENT #endif /* ARCH_RTC_LOCATION */ +bool mc146818_does_rtc_work(void); unsigned int mc146818_get_time(struct rtc_time *time); int mc146818_set_time(struct rtc_time *time); -- cgit v1.2.3 From ec5895c0f2d87b9bf4185db1915e40fa6fcfc0ac Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Mateusz=20Jo=C5=84czyk?= Date: Fri, 10 Dec 2021 21:01:27 +0100 Subject: rtc: mc146818-lib: extract mc146818_avoid_UIP MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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. Therefore, the mechanism in mc146818_get_time() should be reused - so extract it into a separate function. The logic in mc146818_avoid_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 a very unreadable patch, mc146818_get_time() will be refactored to use mc146818_avoid_UIP() in the next patch. Signed-off-by: Mateusz Jończyk Cc: Alessandro Zummo Cc: Alexandre Belloni Signed-off-by: Alexandre Belloni Link: https://lore.kernel.org/r/20211210200131.153887-6-mat.jonczyk@o2.pl --- include/linux/mc146818rtc.h | 3 +++ 1 file changed, 3 insertions(+) (limited to 'include') diff --git a/include/linux/mc146818rtc.h b/include/linux/mc146818rtc.h index 69c80c4325bf..67fb0a12becc 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); +bool mc146818_avoid_UIP(void (*callback)(unsigned char seconds, void *param), + void *param); + #endif /* _MC146818RTC_H */ -- cgit v1.2.3 From 7372971c1be5b7d4fdd8ad237798bdc1d1d54162 Mon Sep 17 00:00:00 2001 From: Dan Carpenter Date: Tue, 11 Jan 2022 10:19:22 +0300 Subject: rtc: mc146818-lib: fix signedness bug in mc146818_get_time() MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit The mc146818_get_time() function returns zero on success or negative a error code on failure. It needs to be type int. Fixes: d35786b3a28d ("rtc: mc146818-lib: change return values of mc146818_get_time()") Signed-off-by: Dan Carpenter Reviewed-by: Mateusz Jończyk Signed-off-by: Alexandre Belloni Link: https://lore.kernel.org/r/20220111071922.GE11243@kili --- include/linux/mc146818rtc.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'include') diff --git a/include/linux/mc146818rtc.h b/include/linux/mc146818rtc.h index 67fb0a12becc..808bb4cee230 100644 --- a/include/linux/mc146818rtc.h +++ b/include/linux/mc146818rtc.h @@ -124,7 +124,7 @@ struct cmos_rtc_board_info { #endif /* ARCH_RTC_LOCATION */ bool mc146818_does_rtc_work(void); -unsigned int mc146818_get_time(struct rtc_time *time); +int mc146818_get_time(struct rtc_time *time); int mc146818_set_time(struct rtc_time *time); bool mc146818_avoid_UIP(void (*callback)(unsigned char seconds, void *param), -- cgit v1.2.3