Patch "rtc: m41t80: avoid i2c read in m41t80_sqw_is_prepared" has been added to the 4.14-stable tree

This is a note to let you know that I've just added the patch titled

    rtc: m41t80: avoid i2c read in m41t80_sqw_is_prepared

to the 4.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:

     rtc-m41t80-avoid-i2c-read-in-m41t80_sqw_is_prepared.patch

and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Troy Kisky <[email protected]>
Date: Thu, 2 Nov 2017 18:58:15 -0700
Subject: rtc: m41t80: avoid i2c read in m41t80_sqw_is_prepared

From: Troy Kisky <[email protected]>

commit 13bb1d78f2e372ec0d9b30489ac63768240140fc upstream.

This is a little more efficient and avoids the warning

WARNING: possible circular locking dependency detected 4.14.0-rc7-00010 #16 Not tainted
------------------------------------------------------
kworker/2:1/70 is trying to acquire lock:
(prepare_lock){+.+.}, at: [<c049300c>] clk_prepare_lock+0x80/0xf4

but task is already holding lock:
(i2c_register_adapter){+.+.}, at: [<c0690b04>]

		i2c_adapter_lock_bus+0x14/0x18

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #1 (i2c_register_adapter){+.+.}:

        rt_mutex_lock+0x44/0x5c
        i2c_adapter_lock_bus+0x14/0x18
        i2c_transfer+0xa8/0xbc
        i2c_smbus_xfer+0x20c/0x5d8
        i2c_smbus_read_byte_data+0x38/0x48
        m41t80_sqw_is_prepared+0x18/0x28

---
 drivers/rtc/rtc-m41t80.c |   15 ++++++---------
 1 file changed, 6 insertions(+), 9 deletions(-)

@@ -155,6 +155,7 @@ struct m41t80_data {
 #ifdef CONFIG_COMMON_CLK
 	struct clk_hw sqw;
 	unsigned long freq;
+	unsigned int sqwe;
 #endif
 };
 

@@ -527,7 +528,10 @@ static int m41t80_sqw_control(struct clk
 	else
 		ret &= ~M41T80_ALMON_SQWE;
 
-	return i2c_smbus_write_byte_data(client, M41T80_REG_ALARM_MON, ret);
+	ret = i2c_smbus_write_byte_data(client, M41T80_REG_ALARM_MON, ret);
+	if (!ret)
+		m41t80->sqwe = enable;
+	return ret;
 }
 
 static int m41t80_sqw_prepare(struct clk_hw *hw)

@@ -542,14 +546,7 @@ static void m41t80_sqw_unprepare(struct
 
 static int m41t80_sqw_is_prepared(struct clk_hw *hw)
 {
-	struct m41t80_data *m41t80 = sqw_to_m41t80_data(hw);
-	struct i2c_client *client = m41t80->client;
-	int ret = i2c_smbus_read_byte_data(client, M41T80_REG_ALARM_MON);
-
-	if (ret < 0)
-		return ret;
-
-	return !!(ret & M41T80_ALMON_SQWE);
+	return sqw_to_m41t80_data(hw)->sqwe;
 }
 
 static const struct clk_ops m41t80_sqw_ops = {

Patches currently in stable-queue which might be from [email protected] are

queue-4.14/rtc-m41t80-m41t80_sqw_set_rate-should-return-0-on-success.patch queue-4.14/rtc-m41t80-avoid-i2c-read-in-m41t80_sqw_is_prepared.patch queue-4.14/rtc-m41t80-avoid-i2c-read-in-m41t80_sqw_recalc_rate.patch queue-4.14/rtc-m41t80-remove-unneeded-checks-from-m41t80_sqw_set_rate.patch queue-4.14/rtc-m41t80-fix-m41t80_sqw_round_rate-return-value.patch