linux-kernel - [PATCH 4.14 13/14] rtc: m41t80: avoid i2c read in m41t80_sqw_is

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Date:   Thu,  4 Jan 2018 13:09:30 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Troy Kisky <troy.kisky@...ndarydevices.com>,
        Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
        Christoph Fritz <chf.fritz@...glemail.com>
Subject: [PATCH 4.14 13/14] rtc: m41t80: avoid i2c read in m41t80_sqw_is_prepared

4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Troy Kisky <troy.kisky@...ndarydevices.com>

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

Signed-off-by: Troy Kisky <troy.kisky@...ndarydevices.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@...e-electrons.com>
Cc: Christoph Fritz <chf.fritz@...glemail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

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

--- a/drivers/rtc/rtc-m41t80.c
+++ b/drivers/rtc/rtc-m41t80.c
@@ -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 = {