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    SubjectRe: [RFC][PATCH] mfd: mc13xxx-core: put mutex lock down to mc13xxx_reg_rmw function
    Hello Axel,

    On Wed, May 04, 2011 at 12:27:59AM +0800, Axel Lin wrote:
    > The mc13xxx_reg_rmw function is doing read/modify/write bitmask operations,
    > thus add the lock to protect it.
    > Then we can remove the lock/unlock from the caller.
    >
    > Signed-off-by: Axel Lin <axel.lin@gmail.com>
    > ---
    > Note I don't have the hardware handy for testing.
    > I appreciate if someone who has the device can test this patch.
    > Regards,
    > Axel
    >
    > drivers/mfd/mc13xxx-core.c | 8 ++++++--
    > drivers/regulator/mc13892-regulator.c | 16 +++++++---------
    > drivers/regulator/mc13xxx-regulator-core.c | 6 ------
    > 3 files changed, 13 insertions(+), 17 deletions(-)
    >
    > diff --git a/drivers/mfd/mc13xxx-core.c b/drivers/mfd/mc13xxx-core.c
    > index 7e4d44b..5fb0fcc 100644
    [snip]
    > diff --git a/drivers/regulator/mc13892-regulator.c b/drivers/regulator/mc13892-regulator.c
    > index 1b8f739..679b315 100644
    > --- a/drivers/regulator/mc13892-regulator.c
    > +++ b/drivers/regulator/mc13892-regulator.c
    > @@ -449,7 +449,8 @@ static int mc13892_sw_regulator_set_voltage(struct regulator_dev *rdev,
    > ret = mc13xxx_reg_read(priv->mc13xxx,
    > mc13892_regulators[id].vsel_reg, &val);
    > if (ret)
    > - goto err;
    > + mc13xxx_unlock(priv->mc13xxx);
    > + return ret;
    >
    > hi = val & MC13892_SWITCHERS0_SWxHI;
    > if (value > 1375)
    > @@ -464,11 +465,10 @@ static int mc13892_sw_regulator_set_voltage(struct regulator_dev *rdev,
    > value = (value - 600000) / 25000;
    >
    > mask = mc13892_regulators[id].vsel_mask | MC13892_SWITCHERS0_SWxHI;
    > - ret = mc13xxx_reg_rmw(priv->mc13xxx, mc13892_regulators[id].vsel_reg,
    > - mask, value << mc13892_regulators[id].vsel_shift);
    > -err:
    > mc13xxx_unlock(priv->mc13xxx);
    >
    > + ret = mc13xxx_reg_rmw(priv->mc13xxx, mc13892_regulators[id].vsel_reg,
    > + mask, value << mc13892_regulators[id].vsel_shift);
    I havn't looked deeply, but I guess this can have unwanted side effects
    here. Before you had:

    lock()
    do(something)
    do(something, else, that, needs, rmw)
    unlock()

    and you introduced an unlock()/lock() between these two do()s.

    I'm not convinced this change is good, though I agree that

    lock()
    rmw(...)
    unlock()

    looks ugly, but imho this can better be fixed by adding a wrapper for
    that sequence if you really want.

    Best regards
    Uwe

    --
    Pengutronix e.K. | Uwe Kleine-König |
    Industrial Linux Solutions | http://www.pengutronix.de/ |
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