rtc: m41t80: avoid i2c read in m41t80_sqw_recalc_rate

This is a little more efficient, and avoids the warning

 WARNING: possible circular locking dependency detected
 4.14.0-rc7-00007 #14 Not tainted
 ------------------------------------------------------
 alsactl/330 is trying to acquire lock:
 (prepare_lock){+.+.}, at: [<c049300c>] clk_prepare_lock+0x80/0xf4

 but task is already holding lock:
 (i2c_register_adapter){+.+.}, at: [<c0690ae0>]
		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_recalc_rate+0x24/0x58

Signed-off-by: Troy Kisky <troy.kisky@boundarydevices.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>

diff --git a/drivers/rtc/rtc-m41t80.c b/drivers/rtc/rtc-m41t80.c
index 42fc735..f44dcf6 100644 (file)
--- a/drivers/rtc/rtc-m41t80.c
+++ b/drivers/rtc/rtc-m41t80.c
@@ -154,6 +154,7 @@ struct m41t80_data {
        struct rtc_device *rtc;
 #ifdef CONFIG_COMMON_CLK
        struct clk_hw sqw;
+       unsigned long freq;
 #endif
 };
 
@@ -443,26 +444,28 @@ static SIMPLE_DEV_PM_OPS(m41t80_pm, m41t80_suspend, m41t80_resume);
 #ifdef CONFIG_COMMON_CLK
 #define sqw_to_m41t80_data(_hw) container_of(_hw, struct m41t80_data, sqw)
 
-static unsigned long m41t80_sqw_recalc_rate(struct clk_hw *hw,
-                                           unsigned long parent_rate)
+static unsigned long m41t80_decode_freq(int setting)
+{
+       return (setting == 0) ? 0 : (setting == 1) ? M41T80_SQW_MAX_FREQ :
+               M41T80_SQW_MAX_FREQ >> setting;
+}
+
+static unsigned long m41t80_get_freq(struct m41t80_data *m41t80)
 {
-       struct m41t80_data *m41t80 = sqw_to_m41t80_data(hw);
        struct i2c_client *client = m41t80->client;
        int reg_sqw = (m41t80->features & M41T80_FEATURE_SQ_ALT) ?
                M41T80_REG_WDAY : M41T80_REG_SQW;
        int ret = i2c_smbus_read_byte_data(client, reg_sqw);
-       unsigned long val = M41T80_SQW_MAX_FREQ;
 
        if (ret < 0)
                return 0;
+       return m41t80_decode_freq(ret >> 4);
+}
 
-       ret >>= 4;
-       if (ret == 0)
-               val = 0;
-       else if (ret > 1)
-               val = val / (1 << ret);
-
-       return val;
+static unsigned long m41t80_sqw_recalc_rate(struct clk_hw *hw,
+                                           unsigned long parent_rate)
+{
+       return sqw_to_m41t80_data(hw)->freq;
 }
 
 static long m41t80_sqw_round_rate(struct clk_hw *hw, unsigned long rate,
@@ -505,6 +508,8 @@ static int m41t80_sqw_set_rate(struct clk_hw *hw, unsigned long rate,
        reg = (reg & 0x0f) | (val << 4);
 
        ret = i2c_smbus_write_byte_data(client, reg_sqw, reg);
+       if (!ret)
+               m41t80->freq = m41t80_decode_freq(val);
        return ret;
 }
 
@@ -579,6 +584,7 @@ static struct clk *m41t80_sqw_register_clk(struct m41t80_data *m41t80)
        init.parent_names = NULL;
        init.num_parents = 0;
        m41t80->sqw.init = &init;
+       m41t80->freq = m41t80_get_freq(m41t80);
 
        /* optional override of the clockname */
        of_property_read_string(node, "clock-output-names", &init.name);