W dniu 24.01.2022 o 14:08, gregkh@xxxxxxxxxxxxxxxxxxx pisze:
> The patch below does not apply to the 5.16-stable tree.
> If someone wants it applied there, or to any other stable or longterm
> tree, then please email the backport, including the original git commit
> id to <stable@xxxxxxxxxxxxxxx>.
>
> thanks,
>
> greg k-h
Wait, this patch was not intended for submission into stable yet, at least not in this form.
Why did it end up in the stable queue?
The return values from mc146818_get_time() changed in between,
so it is natural that it does not apply.
See
commit d35786b3a28dee20 ("rtc: mc146818-lib: change return values of mc146818_get_time()")
Greetings,
Mateusz Jończyk
> ------------------ original commit in Linus's tree ------------------
>
> >From ea6fa4961aab8f90a8aa03575a98b4bda368d4b6 Mon Sep 17 00:00:00 2001
> From: =?UTF-8?q?Mateusz=20Jo=C5=84czyk?= <mat.jonczyk@xxxxx>
> Date: Fri, 10 Dec 2021 21:01:26 +0100
> Subject: [PATCH] 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 <mat.jonczyk@xxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Alessandro Zummo <a.zummo@xxxxxxxxxxxx>
> Cc: Alexandre Belloni <alexandre.belloni@xxxxxxxxxxx>
> Signed-off-by: Alexandre Belloni <alexandre.belloni@xxxxxxxxxxx>
> Link: https://lore.kernel.org/r/20211210200131.153887-5-mat.jonczyk@xxxxx
>
> diff --git a/drivers/rtc/rtc-cmos.c b/drivers/rtc/rtc-cmos.c
> index d0f58cca5c20..b90a603d6b12 100644
> --- a/drivers/rtc/rtc-cmos.c
> +++ b/drivers/rtc/rtc-cmos.c
> @@ -800,16 +800,14 @@ cmos_do_probe(struct device *dev, struct resource *ports, int rtc_irq)
>
> rename_region(ports, dev_name(&cmos_rtc.rtc->dev));
>
> - spin_lock_irq(&rtc_lock);
> -
> - /* Ensure that the RTC is accessible. Bit 6 must be 0! */
> - if ((CMOS_READ(RTC_VALID) & 0x40) != 0) {
> - spin_unlock_irq(&rtc_lock);
> - dev_warn(dev, "not accessible\n");
> + if (!mc146818_does_rtc_work()) {
> + dev_warn(dev, "broken or not accessible\n");
> retval = -ENXIO;
> goto cleanup1;
> }
>
> + spin_lock_irq(&rtc_lock);
> +
> if (!(flags & CMOS_RTC_FLAGS_NOFREQ)) {
> /* force periodic irq to CMOS reset default of 1024Hz;
> *
> diff --git a/drivers/rtc/rtc-mc146818-lib.c b/drivers/rtc/rtc-mc146818-lib.c
> index ccd974b8a75a..d8e67a01220e 100644
> --- a/drivers/rtc/rtc-mc146818-lib.c
> +++ b/drivers/rtc/rtc-mc146818-lib.c
> @@ -8,10 +8,36 @@
> #include <linux/acpi.h>
> #endif
>
> +/*
> + * If the UIP (Update-in-progress) bit of the RTC is set for more then
> + * 10ms, the RTC is apparently broken or not present.
> + */
> +bool mc146818_does_rtc_work(void)
> +{
> + int i;
> + unsigned char val;
> + unsigned long flags;
> +
> + for (i = 0; i < 10; i++) {
> + spin_lock_irqsave(&rtc_lock, flags);
> + val = CMOS_READ(RTC_FREQ_SELECT);
> + spin_unlock_irqrestore(&rtc_lock, flags);
> +
> + if ((val & RTC_UIP) == 0)
> + return true;
> +
> + mdelay(1);
> + }
> +
> + return false;
> +}
> +EXPORT_SYMBOL_GPL(mc146818_does_rtc_work);
> +
> unsigned int mc146818_get_time(struct rtc_time *time)
> {
> unsigned char ctrl;
> unsigned long flags;
> + unsigned int iter_count = 0;
> unsigned char century = 0;
> bool retry;
>
> @@ -20,13 +46,13 @@ unsigned int mc146818_get_time(struct rtc_time *time)
> #endif
>
> again:
> - spin_lock_irqsave(&rtc_lock, flags);
> - /* Ensure that the RTC is accessible. Bit 6 must be 0! */
> - if (WARN_ON_ONCE((CMOS_READ(RTC_VALID) & 0x40) != 0)) {
> - spin_unlock_irqrestore(&rtc_lock, flags);
> + if (iter_count > 10) {
> memset(time, 0, sizeof(*time));
> return -EIO;
> }
> + iter_count++;
> +
> + spin_lock_irqsave(&rtc_lock, flags);
>
> /*
> * Check whether there is an update in progress during which the
> 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);
>
>
