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    Subject[PATCH 4.14 12/14] rtc: m41t80: avoid i2c read in m41t80_sqw_recalc_rate
    Date
    4.14-stable review patch.  If anyone has any objections, please let me know.

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

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

    commit 2cb90ed3de1e279dbaf23df141f54eb9fb1861e6 upstream.

    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>
    Cc: Christoph Fritz <chf.fritz@googlemail.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/rtc/rtc-m41t80.c | 28 +++++++++++++++++-----------
    1 file changed, 17 insertions(+), 11 deletions(-)

    --- 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, m41t
    #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 cl
    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_c
    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);

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