linux-kernel - [tip: timers/urgent] rtc: mc146818: Dont test for bit 0-5 in Register D

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Date:   Tue, 02 Feb 2021 19:40:39 -0000
From:   "tip-bot2 for Thomas Gleixner" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Serge Belyshev <belyshev@...ni.sinp.msu.ru>,
        Dirk Gouders <dirk@...ders.net>, Borislav Petkov <bp@...e.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Len Brown <len.brown@...el.com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        x86@...nel.org, linux-kernel@...r.kernel.org
Subject: [tip: timers/urgent] rtc: mc146818: Dont test for bit 0-5 in Register D

The following commit has been merged into the timers/urgent branch of tip:

Commit-ID:     ebb22a05943666155e6da04407cc6e913974c78c
Gitweb:        https://git.kernel.org/tip/ebb22a05943666155e6da04407cc6e913974c78c
Author:        Thomas Gleixner <tglx@...utronix.de>
AuthorDate:    Mon, 01 Feb 2021 20:24:17 +01:00
Committer:     Thomas Gleixner <tglx@...utronix.de>
CommitterDate: Tue, 02 Feb 2021 20:35:02 +01:00

rtc: mc146818: Dont test for bit 0-5 in Register D

The recent change to validate the RTC turned out to be overly tight.

While it cures the problem on the reporters machine it breaks machines
with Intel chipsets which use bit 0-5 of the D register. So check only
for bit 6 being 0 which is the case on these Intel machines as well.

Fixes: 211e5db19d15 ("rtc: mc146818: Detect and handle broken RTCs")
Reported-by: Serge Belyshev <belyshev@...ni.sinp.msu.ru>
Reported-by: Dirk Gouders <dirk@...ders.net>
Reported-by: Borislav Petkov <bp@...e.de>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Tested-by: Dirk Gouders <dirk@...ders.net>
Tested-by: Len Brown <len.brown@...el.com>
Tested-by: Borislav Petkov <bp@...e.de>
Acked-by: Alexandre Belloni <alexandre.belloni@...tlin.com>
Link: https://lore.kernel.org/r/87zh0nbnha.fsf@nanos.tec.linutronix.de

---
 drivers/rtc/rtc-cmos.c         | 4 ++--
 drivers/rtc/rtc-mc146818-lib.c | 4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/rtc/rtc-cmos.c b/drivers/rtc/rtc-cmos.c
index 68a9ac6..a701dae 100644
--- a/drivers/rtc/rtc-cmos.c
+++ b/drivers/rtc/rtc-cmos.c
@@ -805,8 +805,8 @@ cmos_do_probe(struct device *dev, struct resource *ports, int rtc_irq)
 
 	spin_lock_irq(&rtc_lock);
 
-	/* Ensure that the RTC is accessible. Bit 0-6 must be 0! */
-	if ((CMOS_READ(RTC_VALID) & 0x7f) != 0) {
+	/* 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");
 		retval = -ENXIO;
diff --git a/drivers/rtc/rtc-mc146818-lib.c b/drivers/rtc/rtc-mc146818-lib.c
index f83c138..dcfaf09 100644
--- a/drivers/rtc/rtc-mc146818-lib.c
+++ b/drivers/rtc/rtc-mc146818-lib.c
@@ -21,8 +21,8 @@ unsigned int mc146818_get_time(struct rtc_time *time)
 
 again:
 	spin_lock_irqsave(&rtc_lock, flags);
-	/* Ensure that the RTC is accessible. Bit 0-6 must be 0! */
-	if (WARN_ON_ONCE((CMOS_READ(RTC_VALID) & 0x7f) != 0)) {
+	/* 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);
 		memset(time, 0xff, sizeof(*time));
 		return 0;