Re: [PATCH v2] Staging: iio: ade7758: expand buf_lock to cover both buffer and state protection

From: Jonathan Cameron
Date: Sun Jan 28 2018 - 03:35:20 EST

On Thu, 25 Jan 2018 22:10:08 +0530
Shreeya Patel <shreeya.patel23498@xxxxxxxxx> wrote:

> iio_dev->mlock is to be used only by the IIO core for protecting
> device mode changes between INDIO_DIRECT and INDIO_BUFFER.
>
> This patch replaces the use of mlock with the already established
> buf_lock mutex.
>
> Introducing 'unlocked' __ade7758_spi_write_reg_8 and
> __ade7758_spi_read_reg_8 functions to be used by ade7758_write_samp_freq
> and ade7758_read_samp_freq which avoids nested locks and maintains
> atomicity between bus and device frequency changes.
>
> Signed-off-by: Shreeya Patel <shreeya.patel23498@xxxxxxxxx>
Hi Shreeya,

This is now technically correct which is great.
I would make one minor change to make it slightly easier to read.

The read / write frequency functions now require the buf_lock to
be held. That's not obvious so I would avoid this but moving
the locking inside the functions where it is then clear that
they are taking the unlocked forms of the register read/ write.

This would also then make it clear why the normal locked form
of _read_reg_8 is fine in the read_freq case but not the
write_freq case. (Hence just use the normal locked form
for the read and don't explicitly take the locks when
reading the frequency - leave it to the register read function)

Thanks,

Jonathan
> ---
>
> Changes in v2
> -Add static keyword to newly introduced functions and remove some
> added comments which are not required.
>
>
> drivers/staging/iio/meter/ade7758.h | 2 +-
> drivers/staging/iio/meter/ade7758_core.c | 47 +++++++++++++++++++++++---------
> 2 files changed, 35 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/staging/iio/meter/ade7758.h b/drivers/staging/iio/meter/ade7758.h
> index 6ae78d8..2de81b5 100644
> --- a/drivers/staging/iio/meter/ade7758.h
> +++ b/drivers/staging/iio/meter/ade7758.h
> @@ -111,7 +111,7 @@
> * @trig: data ready trigger registered with iio
> * @tx: transmit buffer
> * @rx: receive buffer
> - * @buf_lock: mutex to protect tx and rx
> + * @buf_lock: mutex to protect tx, rx, read and write frequency
> **/
> struct ade7758_state {
> struct spi_device *us;
> diff --git a/drivers/staging/iio/meter/ade7758_core.c b/drivers/staging/iio/meter/ade7758_core.c
> index 7b7ffe5..fed4684 100644
> --- a/drivers/staging/iio/meter/ade7758_core.c
> +++ b/drivers/staging/iio/meter/ade7758_core.c
> @@ -24,17 +24,25 @@
> #include "meter.h"
> #include "ade7758.h"
>
> -int ade7758_spi_write_reg_8(struct device *dev, u8 reg_address, u8 val)
> +static int __ade7758_spi_write_reg_8(struct device *dev, u8 reg_address, u8 val)
> {
> - int ret;
> struct iio_dev *indio_dev = dev_to_iio_dev(dev);
> struct ade7758_state *st = iio_priv(indio_dev);
>
> - mutex_lock(&st->buf_lock);
> st->tx[0] = ADE7758_WRITE_REG(reg_address);
> st->tx[1] = val;
>
> - ret = spi_write(st->us, st->tx, 2);
> + return spi_write(st->us, st->tx, 2);
> +}
> +
> +int ade7758_spi_write_reg_8(struct device *dev, u8 reg_address, u8 val)
> +{
> + int ret;
> + struct iio_dev *indio_dev = dev_to_iio_dev(dev);
> + struct ade7758_state *st = iio_priv(indio_dev);
> +
> + mutex_lock(&st->buf_lock);
> + ret = __ade7758_spi_write_reg_8(dev, reg_address, val);
> mutex_unlock(&st->buf_lock);
>
> return ret;
> @@ -91,7 +99,7 @@ static int ade7758_spi_write_reg_24(struct device *dev, u8 reg_address,
> return ret;
> }
>
> -int ade7758_spi_read_reg_8(struct device *dev, u8 reg_address, u8 *val)
> +static int __ade7758_spi_read_reg_8(struct device *dev, u8 reg_address, u8 *val)
> {
> struct iio_dev *indio_dev = dev_to_iio_dev(dev);
> struct ade7758_state *st = iio_priv(indio_dev);
> @@ -111,7 +119,6 @@ int ade7758_spi_read_reg_8(struct device *dev, u8 reg_address, u8 *val)
> },
> };
>
> - mutex_lock(&st->buf_lock);
> st->tx[0] = ADE7758_READ_REG(reg_address);
> st->tx[1] = 0;
>
> @@ -124,7 +131,19 @@ int ade7758_spi_read_reg_8(struct device *dev, u8 reg_address, u8 *val)
> *val = st->rx[0];
>
> error_ret:
> + return ret;
> +}
> +
> +int ade7758_spi_read_reg_8(struct device *dev, u8 reg_address, u8 *val)
> +{
> + struct iio_dev *indio_dev = dev_to_iio_dev(dev);
> + struct ade7758_state *st = iio_priv(indio_dev);
> + int ret;
> +
> + mutex_lock(&st->buf_lock);
> + ret = __ade7758_spi_read_reg_8(dev, reg_address, val);
> mutex_unlock(&st->buf_lock);
> +
> return ret;
> }
>
> @@ -470,7 +489,7 @@ static int ade7758_read_samp_freq(struct device *dev, int *val)
> int ret;
> u8 t;
>
> - ret = ade7758_spi_read_reg_8(dev, ADE7758_WAVMODE, &t);
> + ret = __ade7758_spi_read_reg_8(dev, ADE7758_WAVMODE, &t);
> if (ret)
> return ret;
>
> @@ -503,14 +522,14 @@ static int ade7758_write_samp_freq(struct device *dev, int val)
> goto out;
> }
>
> - ret = ade7758_spi_read_reg_8(dev, ADE7758_WAVMODE, &reg);
> + ret = __ade7758_spi_read_reg_8(dev, ADE7758_WAVMODE, &reg);
> if (ret)
> goto out;
>
> reg &= ~(5 << 3);
> reg |= t << 5;
>
> - ret = ade7758_spi_write_reg_8(dev, ADE7758_WAVMODE, reg);
> + ret = __ade7758_spi_write_reg_8(dev, ADE7758_WAVMODE, reg);
>
> out:
> return ret;
> @@ -523,12 +542,13 @@ static int ade7758_read_raw(struct iio_dev *indio_dev,
> long mask)
> {
> int ret;
> + struct ade7758_state *st = iio_priv(indio_dev);
>
> switch (mask) {
> case IIO_CHAN_INFO_SAMP_FREQ:
> - mutex_lock(&indio_dev->mlock);
> + mutex_lock(&st->buf_lock);
> ret = ade7758_read_samp_freq(&indio_dev->dev, val);
> - mutex_unlock(&indio_dev->mlock);
> + mutex_unlock(&st->buf_lock);
> return ret;
> default:
> return -EINVAL;
> @@ -542,14 +562,15 @@ static int ade7758_write_raw(struct iio_dev *indio_dev,
> int val, int val2, long mask)
> {
> int ret;
> + struct ade7758_state *st = iio_priv(indio_dev);
>
> switch (mask) {
> case IIO_CHAN_INFO_SAMP_FREQ:
> if (val2)
> return -EINVAL;
> - mutex_lock(&indio_dev->mlock);
> + mutex_lock(&st->buf_lock);
> ret = ade7758_write_samp_freq(&indio_dev->dev, val);
> - mutex_unlock(&indio_dev->mlock);
> + mutex_unlock(&st->buf_lock);
> return ret;
> default:
> return -EINVAL;