[PATCH 1/5] iio: adc: spear_adc: Replace indio_dev->mlock with own device lock

Mircea Caprioru
2020-09-28T13:14:24Z

From: Sergiu Cuciurean <sergiu.cuciurean@analog.com>

As part of the general cleanup of indio_dev->mlock, this change replaces
it with a local lock on the device's state structure.

This is part of a bigger cleanup.
Link: https://lore.kernel.org/linux-iio/CA+U=Dsoo6YABe5ODLp+eFNPGFDjk5ZeQEceGkqjxXcVEhLWubw@mail.gmail.com/

Signed-off-by: Sergiu Cuciurean <sergiu.cuciurean@analog.com>
Signed-off-by: Mircea Caprioru <mircea.caprioru@analog.com>
---
drivers/iio/adc/spear_adc.c | 20 ++++++++++++++++----
1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/drivers/iio/adc/spear_adc.c b/drivers/iio/adc/spear_adc.c
index 1bc986a7009d..d93e580b3dc5 100644
--- a/drivers/iio/adc/spear_adc.c
+++ b/drivers/iio/adc/spear_adc.c
@@ -75,6 +75,15 @@ struct spear_adc_state {
struct adc_regs_spear6xx __iomem *adc_base_spear6xx;
struct clk *clk;
struct completion completion;
+ /*
+ * Lock to protect the device state during a potential concurrent
+ * read access from userspace. Reading a raw value requires a sequence
+ * of register writes, then a wait for a completion callback,
+ * and finally a register read, during which userspace could issue
+ * another read request. This lock protects a read access from
+ * ocurring before another one has finished.
+ */
+ struct mutex lock;
u32 current_clk;
u32 sampling_freq;
u32 avg_samples;
@@ -146,7 +155,7 @@ static int spear_adc_read_raw(struct iio_dev *indio_dev,

switch (mask) {
case IIO_CHAN_INFO_RAW:
- mutex_lock(&indio_dev->mlock);
+ mutex_lock(&st->lock);

status = SPEAR_ADC_STATUS_CHANNEL_NUM(chan->channel) |
SPEAR_ADC_STATUS_AVG_SAMPLE(st->avg_samples) |
@@ -159,7 +168,7 @@ static int spear_adc_read_raw(struct iio_dev *indio_dev,
wait_for_completion(&st->completion); /* set by ISR */
*val = st->value;

- mutex_unlock(&indio_dev->mlock);
+ mutex_unlock(&st->lock);

return IIO_VAL_INT;

@@ -187,7 +196,7 @@ static int spear_adc_write_raw(struct iio_dev *indio_dev,
if (mask != IIO_CHAN_INFO_SAMP_FREQ)
return -EINVAL;

- mutex_lock(&indio_dev->mlock);
+ mutex_lock(&st->lock);

if ((val < SPEAR_ADC_CLK_MIN) ||
(val > SPEAR_ADC_CLK_MAX) ||
@@ -199,7 +208,7 @@ static int spear_adc_write_raw(struct iio_dev *indio_dev,
spear_adc_set_clk(st, val);

out:
- mutex_unlock(&indio_dev->mlock);
+ mutex_unlock(&st->lock);
return ret;
}

@@ -271,6 +280,9 @@ static int spear_adc_probe(struct platform_device *pdev)
}

st = iio_priv(indio_dev);
+
+ mutex_init(&st->lock);
+
st->np = np;

/*
--
2.25.1