linux-kernel - [PATCH v2 7/9] rtc: isl12022: drop redundant write to HR register

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Wed, 21 Sep 2022 13:46:22 +0200
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Alessandro Zummo <a.zummo@...ertech.it>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>
Cc:     Rasmus Villemoes <linux@...musvillemoes.dk>,
        linux-rtc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v2 7/9] rtc: isl12022: drop redundant write to HR register

There's nothing in the data sheet that says writing to one of the time
keeping registers is necessary to start the RTC. It does so at the
stop condition of the i2c transfer setting the WRTC bit:

  Upon initialization or power-up, the WRTC must be set to "1" to
  enable the RTC. Upon the completion of a valid write (STOP), the RTC
  starts counting.

Moreover, even if such a write to one of the timekeeping registers was
necessary, that's exactly what we do anyway just below when we
actually write the given struct rtc_time to the device.

Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
---
 drivers/rtc/rtc-isl12022.c | 14 --------------
 1 file changed, 14 deletions(-)

diff --git a/drivers/rtc/rtc-isl12022.c b/drivers/rtc/rtc-isl12022.c
index df6d91f4e8f3..6fb13a5d17f1 100644
--- a/drivers/rtc/rtc-isl12022.c
+++ b/drivers/rtc/rtc-isl12022.c
@@ -171,20 +171,6 @@ static int isl12022_rtc_set_time(struct device *dev, struct rtc_time *tm)
 						 buf[0] | ISL12022_INT_WRTC);
 			if (ret)
 				return ret;
-
-			/* Write to any RTC register to start RTC, we use the
-			 * HR register, setting the MIL bit to use the 24 hour
-			 * format. */
-			ret = isl12022_read_regs(client, ISL12022_REG_HR,
-						 buf, 1);
-			if (ret)
-				return ret;
-
-			ret = isl12022_write_reg(client,
-						 ISL12022_REG_HR,
-						 buf[0] | ISL12022_HR_MIL);
-			if (ret)
-				return ret;
 		}
 
 		isl12022->write_enabled = true;
-- 
2.37.2