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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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