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Mateusz Jończyk 985d87e6a3 rtc: mc146818-lib: fix RTC presence check 
[ Upstream commit ea6fa4961a ]

To prevent an infinite loop in mc146818_get_time(),
commit 211e5db19d ("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: 211e5db19d ("rtc: mc146818: Detect and handle broken RTCs")
Fixes: ebb22a0594 ("rtc: mc146818: Dont test for bit 0-5 in Register D")
Signed-off-by: Mateusz Jończyk <mat.jonczyk@o2.pl>
Cc: Thomas Gleixner <tglx@linutronix.de>
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/20211210200131.153887-5-mat.jonczyk@o2.pl
Signed-off-by: Sasha Levin <sashal@kernel.org>
2022-04-13 20:59:14 +02:00
..
class.c rtc: class: remove bogus documentation 2021-02-06 00:58:24 +01:00
dev.c compat_ioctl: move rtc handling into drivers/rtc/dev.c 2019-10-23 17:23:43 +02:00
interface.c rtc: check if __rtc_read_time was successful 2022-04-08 14:24:10 +02:00
Kconfig rtc: rx8010: select REGMAP_I2C 2021-09-09 10:18:40 +02:00
lib.c rtc: Improve performance of rtc_time64_to_tm(). Add tests. 2021-08-10 00:09:21 +02:00
lib_test.c rtc: lib_test: add MODULE_LICENSE 2021-08-10 23:21:46 +02:00
Makefile rtc: move RTC_LIB_KUNIT_TEST to proper location 2021-08-10 23:22:20 +02:00
nvmem.c rtc: nvmem: emit an error message when nvmem registration fails 2020-11-19 12:50:12 +01:00
proc.c rtc: fix snprintf() checking in is_rtc_hctosys() 2021-05-25 00:36:11 +02:00
rtc-88pm80x.c rtc: rework rtc_register_device() resource management 2020-11-19 12:50:12 +01:00
rtc-88pm860x.c rtc: rework rtc_register_device() resource management 2020-11-19 12:50:12 +01:00
rtc-ab-b5ze-s3.c rtc: rework rtc_register_device() resource management 2020-11-19 12:50:12 +01:00
rtc-ab-eoz9.c rtc: ab-eoz9: make use of RTC_FEATURE_ALARM 2021-04-17 00:07:16 +02:00
rtc-ab8500.c rtc: rework rtc_register_device() resource management 2020-11-19 12:50:12 +01:00
rtc-abx80x.c rtc: abx80x: Add utility function for writing configuration key 2021-02-13 23:03:26 +01:00
rtc-ac100.c rtc: ac100: use rtc_lock/rtc_unlock 2021-01-25 23:45:37 +01:00
rtc-armada38x.c rtc: armada38x: remove armada38x_rtc_ops_noirq 2021-01-16 23:19:26 +01:00
rtc-as3722.c
rtc-asm9260.c rtc: asm9260: use rtc_lock/rtc_unlock 2021-01-25 23:46:16 +01:00
rtc-aspeed.c rtc: rework rtc_register_device() resource management 2020-11-19 12:50:12 +01:00
rtc-at91rm9200.c rtc: rework rtc_register_device() resource management 2020-11-19 12:50:12 +01:00
rtc-at91sam9.c rtc: at91sam9: Remove unnecessary offset variable checks 2021-07-10 02:42:08 +02:00
rtc-au1xxx.c rtc: au1xxx: convert to SPDX identifier 2021-07-10 01:53:39 +02:00
rtc-bd70528.c rtc: bd70528: Drop BD70528 support 2021-06-20 22:24:52 +02:00
rtc-bq32k.c rtc: bq32k: quiet maybe-unused variable warning 2021-02-06 00:58:24 +01:00
rtc-bq4802.c
rtc-brcmstb-waketimer.c rtc: brcmstb-waketimer: quiet maybe-unused variable warning 2021-02-06 00:58:24 +01:00
rtc-cadence.c rtc: rework rtc_register_device() resource management 2020-11-19 12:50:12 +01:00
rtc-cmos.c rtc: mc146818-lib: fix RTC presence check 2022-04-13 20:59:14 +02:00
rtc-core.h
rtc-cpcap.c rtc: rework rtc_register_device() resource management 2020-11-19 12:50:12 +01:00
rtc-cros-ec.c rtc: rework rtc_register_device() resource management 2020-11-19 12:50:12 +01:00
rtc-da9052.c rtc: rework rtc_register_device() resource management 2020-11-19 12:50:12 +01:00
rtc-da9055.c
rtc-da9063.c rtc: rework rtc_register_device() resource management 2020-11-19 12:50:12 +01:00
rtc-davinci.c rtc: rework rtc_register_device() resource management 2020-11-19 12:50:12 +01:00
rtc-digicolor.c rtc: digicolor: quiet maybe-unused variable warning 2021-02-06 00:58:24 +01:00
rtc-dm355evm.c rtc: rework rtc_register_device() resource management 2020-11-19 12:50:12 +01:00
rtc-ds1216.c rtc: use devm_platform_ioremap_resource() to simplify code 2019-10-07 01:07:35 +02:00
rtc-ds1286.c rtc: use devm_platform_ioremap_resource() to simplify code 2019-10-07 01:07:35 +02:00
rtc-ds1302.c rtc: ds1302: Add SPI ID table 2021-11-18 19:16:58 +01:00
rtc-ds1305.c rtc: ds1305: use rtc_lock/rtc_unlock 2021-01-25 23:46:16 +01:00
rtc-ds1307.c rtc: ds1307: Fix wday settings for rx8130 2021-04-29 23:37:18 +02:00
rtc-ds1343.c rtc: rework rtc_register_device() resource management 2020-11-19 12:50:12 +01:00
rtc-ds1347.c rtc: rework rtc_register_device() resource management 2020-11-19 12:50:12 +01:00
rtc-ds1374.c rtc: ds1374: convert to SPDX identifier 2021-07-10 01:53:39 +02:00
rtc-ds1390.c rtc: ds1390: Add SPI ID table 2021-11-18 19:16:59 +01:00
rtc-ds1511.c rtc: ds1511: remove unused function 2021-04-17 11:21:04 +02:00
rtc-ds1553.c rtc: rework rtc_register_device() resource management 2020-11-19 12:50:12 +01:00
rtc-ds1672.c rtc: ds1672: quiet maybe-unused variable warning 2021-02-06 00:58:24 +01:00
rtc-ds1685.c rtc: ds1685: use rtc_lock/rtc_unlock 2021-01-25 23:46:17 +01:00
rtc-ds1742.c rtc: rework rtc_register_device() resource management 2020-11-19 12:50:12 +01:00
rtc-ds2404.c rtc: rework rtc_register_device() resource management 2020-11-19 12:50:12 +01:00
rtc-ds3232.c rtc: ds3232: quiet maybe-unused variable warning 2021-02-06 00:58:24 +01:00
rtc-efi.c rtc: efi: Remove the repeated module alias 2021-05-25 00:39:58 +02:00
rtc-em3027.c rtc: em3027: correct month value 2019-11-08 16:14:09 +01:00
rtc-ep93xx.c rtc: ep93xx: Fix NULL pointer dereference in ep93xx_rtc_read_time 2020-12-03 23:49:31 +01:00
rtc-fm3130.c
rtc-fsl-ftm-alarm.c rtc: fsl-ftm-alarm: add MODULE_TABLE() 2021-04-17 11:21:04 +02:00
rtc-ftrtc010.c rtc: rework rtc_register_device() resource management 2020-11-19 12:50:12 +01:00
rtc-generic.c
rtc-goldfish.c rtc: rework rtc_register_device() resource management 2020-11-19 12:50:12 +01:00
rtc-hid-sensor-time.c iio: hid-sensors: lighten exported symbols by moving to IIO_HID namespace 2021-06-16 14:53:13 +01:00
rtc-hym8563.c rtc: hym8563: use rtc_lock/rtc_unlock 2021-01-25 23:46:17 +01:00
rtc-imx-sc.c rtc: imx-sc: remove .read_alarm 2021-04-29 23:03:26 +02:00
rtc-imxdi.c rtc: imxdi: add wakeup support 2021-05-25 00:41:25 +02:00
rtc-isl1208.c rtc: isl1208: quiet maybe-unused variable warning 2021-02-06 00:58:24 +01:00
rtc-isl12022.c
rtc-isl12026.c rtc: rework rtc_register_device() resource management 2020-11-19 12:50:12 +01:00
rtc-jz4740.c rtc: rework rtc_register_device() resource management 2020-11-19 12:50:12 +01:00
rtc-lp8788.c
rtc-lpc24xx.c rtc: remove unnecessary error message after platform_get_irq 2020-04-15 09:56:17 +02:00
rtc-lpc32xx.c rtc: rework rtc_register_device() resource management 2020-11-19 12:50:12 +01:00
rtc-ls1x.c rtc: rework rtc_register_device() resource management 2020-11-19 12:50:12 +01:00
rtc-m41t80.c rtc: m41t80: correct kerneldoc function names 2021-06-20 22:19:46 +02:00
rtc-m41t93.c
rtc-m41t94.c
rtc-m48t35.c rtc: m48t35: remove SGI-IP27 kludge 2020-03-16 11:12:11 +01:00
rtc-m48t59.c rtc: m48t59: use platform_get_irq_optional 2021-03-11 09:48:09 +01:00
rtc-m48t86.c rtc: rework rtc_register_device() resource management 2020-11-19 12:50:12 +01:00
rtc-max6900.c rtc: max6900: convert to SPDX identifier 2021-07-10 01:53:39 +02:00
rtc-max6902.c
rtc-max6916.c
rtc-max8907.c
rtc-max8925.c
rtc-max8997.c
rtc-max8998.c
rtc-max77686.c rtc: max77686: Do not enforce (incorrect) interrupt trigger type 2021-06-20 22:22:13 +02:00
rtc-mc13xxx.c rtc: rework rtc_register_device() resource management 2020-11-19 12:50:12 +01:00
rtc-mc146818-lib.c rtc: mc146818-lib: fix RTC presence check 2022-04-13 20:59:14 +02:00
rtc-mcp795.c rtc: mcp795: Add SPI ID table 2021-11-18 19:16:59 +01:00
rtc-meson-vrtc.c rtc: rework rtc_register_device() resource management 2020-11-19 12:50:12 +01:00
rtc-meson.c rtc: meson: quiet maybe-unused variable warning 2021-02-06 00:58:24 +01:00
rtc-moxart.c rtc: moxart: Convert to SPDX identifier 2019-12-23 11:23:49 +01:00
rtc-mpc5121.c rtc: rework rtc_register_device() resource management 2020-11-19 12:50:12 +01:00
rtc-msm6242.c rtc: msm6242: Remove unneeded msm6242_set()/msm6242_clear() functions 2019-11-18 15:23:54 +01:00
rtc-mt2712.c rtc: rework rtc_register_device() resource management 2020-11-19 12:50:12 +01:00
rtc-mt6397.c rtc: mt6397: refine RTC_TC_MTH 2021-06-01 16:44:09 +01:00
rtc-mt7622.c rtc: use devm_platform_ioremap_resource() to simplify code 2019-10-07 01:07:35 +02:00
rtc-mv.c rtc: mv: remove mv_rtc_alarm_ops 2021-01-16 23:19:26 +01:00
rtc-mxc.c rtc: mxc: Remove unneeded of_match_ptr() 2021-03-16 08:48:44 +01:00
rtc-mxc_v2.c rtc: mxc_v2: add missing MODULE_DEVICE_TABLE 2021-05-25 00:33:17 +02:00
rtc-ntxec.c rtc: New driver for RTC in Netronix embedded controller 2021-03-10 11:06:33 +00:00
rtc-omap.c rtc: omap: use rtc_write to access OMAP_RTC_OSC_REG 2021-04-29 23:37:18 +02:00
rtc-opal.c rtc: opal: constify opal_rtc_ops 2021-01-16 23:19:26 +01:00
rtc-palmas.c rtc: palmas: convert to SPDX identifier 2021-07-10 01:53:39 +02:00
rtc-pcap.c rtc: rework rtc_register_device() resource management 2020-11-19 12:50:12 +01:00
rtc-pcf2123.c rtc: pcf2123: Add SPI ID table 2021-11-18 19:16:59 +01:00
rtc-pcf2127.c rtc: pcf2127: handle timestamp interrupts 2021-07-10 02:58:31 +02:00
rtc-pcf8523.c rtc: pcf8523: rename register and bit defines 2021-07-10 23:18:30 +02:00
rtc-pcf8563.c rtc: pcf8563: Fix the datasheet URL 2021-06-20 23:48:35 +02:00
rtc-pcf8583.c
rtc-pcf50633.c
rtc-pcf85063.c rtc: pcf85063: Update the PCF85063A datasheet revision 2021-07-10 01:40:49 +02:00
rtc-pcf85363.c rtc: pcf85363: quiet maybe-unused variable warning 2021-02-06 00:58:25 +01:00
rtc-pic32.c rtc: rework rtc_register_device() resource management 2020-11-19 12:50:12 +01:00
rtc-pl030.c amba: Make the remove callback return void 2021-02-02 14:25:50 +01:00
rtc-pl031.c rtc: pl031: fix rtc features null pointer dereference 2022-04-08 14:22:56 +02:00
rtc-pm8xxx.c rtc: pm8xxx: Add RTC support for PMIC PMK8350 2021-04-17 00:20:01 +02:00
rtc-ps3.c rtc: rework rtc_register_device() resource management 2020-11-19 12:50:12 +01:00
rtc-pxa.c rtc: pxa: fix null pointer dereference 2022-01-27 11:05:34 +01:00
rtc-r7301.c rtc: r7301: Replace spin_lock_irqsave with spin_lock in hard IRQ 2021-02-06 00:50:47 +01:00
rtc-r9701.c rtc: rework rtc_register_device() resource management 2020-11-19 12:50:12 +01:00
rtc-rc5t583.c
rtc-rc5t619.c rtc: rework rtc_register_device() resource management 2020-11-19 12:50:12 +01:00
rtc-rk808.c rtc: rework rtc_register_device() resource management 2020-11-19 12:50:12 +01:00
rtc-rp5c01.c rtc: rework rtc_register_device() resource management 2020-11-19 12:50:12 +01:00
rtc-rs5c313.c rtc: rtc-rs5c313: Convert to module_platform_driver() 2020-08-21 00:13:44 +02:00
rtc-rs5c348.c rtc: rework rtc_register_device() resource management 2020-11-19 12:50:12 +01:00
rtc-rs5c372.c rtc: rs5c372: quiet maybe-unused variable warning 2021-02-06 00:58:25 +01:00
rtc-rtd119x.c rtc: rtd119x: Fix format of SPDX identifier 2021-07-10 01:53:39 +02:00
rtc-rv3028.c rtc: rv3028: correct weekday register usage 2021-03-15 23:03:27 +01:00
rtc-rv3029c2.c rtc: rv3029: quiet maybe-unused variable warning 2021-02-06 00:58:25 +01:00
rtc-rv3032.c rtc: rv3032: fix error handling in rv3032_clkout_set_rate() 2021-11-18 19:17:01 +01:00
rtc-rv8803.c rtc: rv8803: quiet maybe-unused variable warning 2021-02-06 00:58:25 +01:00
rtc-rx4581.c
rtc-rx6110.c rtc: rx6110: add ACPI bindings to I2C 2021-03-23 22:23:22 +01:00
rtc-rx8010.c rtc: rx8010: quiet maybe-unused variable warning 2021-02-06 00:58:25 +01:00
rtc-rx8025.c rtc: rx8025: implement RX-8035 support 2021-08-17 23:48:33 +02:00
rtc-rx8581.c rtc: rx8581: quiet maybe-unused variable warning 2021-02-06 00:58:25 +01:00
rtc-s3c.c rtc: s3c: quiet maybe-unused variable warning 2021-02-06 00:59:16 +01:00
rtc-s3c.h
rtc-s5m.c rtc: s5m: set range 2021-08-06 10:31:59 +02:00
rtc-s35390a.c rtc: s35390a: quiet maybe-unused variable warning 2021-02-06 00:58:25 +01:00
rtc-sa1100.c rtc: rework rtc_register_device() resource management 2020-11-19 12:50:12 +01:00
rtc-sa1100.h
rtc-sc27xx.c rtc: sc27xx: Fix format of SPDX identifier 2021-07-10 01:53:39 +02:00
rtc-sd3078.c rtc: sd3078: quiet maybe-unused variable warning 2021-02-06 00:58:26 +01:00
rtc-sh.c rtc: rework rtc_register_device() resource management 2020-11-19 12:50:12 +01:00
rtc-snvs.c rtc: rework rtc_register_device() resource management 2020-11-19 12:50:12 +01:00
rtc-spear.c rtc: spear: convert to SPDX identifier 2021-07-10 01:53:57 +02:00
rtc-st-lpc.c rtc: rework rtc_register_device() resource management 2020-11-19 12:50:12 +01:00
rtc-starfire.c rtc: rework rtc_register_device() resource management 2020-11-19 12:50:12 +01:00
rtc-stk17ta8.c rtc: rework rtc_register_device() resource management 2020-11-19 12:50:12 +01:00
rtc-stm32.c rtc: stm32: Fix unbalanced clk_disable_unprepare() on probe error path 2021-06-20 22:28:02 +02:00
rtc-stmp3xxx.c rtc: rework rtc_register_device() resource management 2020-11-19 12:50:12 +01:00
rtc-sun4v.c rtc: rework rtc_register_device() resource management 2020-11-19 12:50:12 +01:00
rtc-sun6i.c rtc: rework rtc_register_device() resource management 2020-11-19 12:50:12 +01:00
rtc-sunxi.c rtc: rework rtc_register_device() resource management 2020-11-19 12:50:12 +01:00
rtc-tegra.c rtc: tegra: Replace spin_lock_irqsave with spin_lock in hard IRQ 2021-02-06 00:50:47 +01:00
rtc-test.c rtc: test: remove debug message 2020-12-03 23:43:23 +01:00
rtc-tps6586x.c rtc: tps6586x: convert to SPDX identifier 2021-07-10 01:53:40 +02:00
rtc-tps65910.c rtc: tps65910: Correct driver module alias 2021-08-17 23:36:22 +02:00
rtc-tps80031.c rtc: tps80031: convert to SPDX identifier 2021-07-10 01:53:39 +02:00
rtc-twl.c
rtc-v3020.c rtc: v3020: remove redundant initialization of variable retval 2021-06-20 22:29:50 +02:00
rtc-vr41xx.c rtc: rework rtc_register_device() resource management 2020-11-19 12:50:12 +01:00
rtc-vt8500.c rtc: rework rtc_register_device() resource management 2020-11-19 12:50:12 +01:00
rtc-wilco-ec.c rtc: rework rtc_register_device() resource management 2020-11-19 12:50:12 +01:00
rtc-wm831x.c rtc: rework rtc_register_device() resource management 2020-11-19 12:50:12 +01:00
rtc-wm8350.c rtc: wm8350: Handle error for wm8350_register_irq 2022-04-13 20:58:59 +02:00
rtc-x1205.c
rtc-xgene.c rtc: rework rtc_register_device() resource management 2020-11-19 12:50:12 +01:00
rtc-zynqmp.c rtc: rework rtc_register_device() resource management 2020-11-19 12:50:12 +01:00
sysfs.c rtc: sysfs: Correct kerneldoc function name hctosys_show() 2021-06-20 22:18:05 +02:00