[PATCH v5 3/5] iio: pac1921: use read_avail+release APIs instead of custom ext_info

Matteo Martelli
2024-10-21T12:56:29Z

The pac1921 driver was exposing the available scale info via an ad-hoc
ext_info attribute instead of using the read_avail API. This to avoid a
possible race condition: while the available current scales were being
printed to sysfs by iio core (iio_read_channel_info_avail), the shunt
resistor might have been changed concurrently.

Switch to the read_avail+release APIs now that the race condition has
been addressed.

Signed-off-by: Matteo Martelli <matteomartelli3@gmail.com>
---
drivers/iio/adc/pac1921.c | 128 ++++++++++++++++------------------------------
1 file changed, 45 insertions(+), 83 deletions(-)

diff --git a/drivers/iio/adc/pac1921.c b/drivers/iio/adc/pac1921.c
index a96fae546bc1e6d1bf3a0dbe67204c191d77a3ee..f6f8f9122a78d1b5e63d8184203eb3dae55eb560 100644
--- a/drivers/iio/adc/pac1921.c
+++ b/drivers/iio/adc/pac1921.c
@@ -444,11 +444,52 @@ static int pac1921_read_avail(struct iio_dev *indio_dev,
*vals = pac1921_int_num_samples;
*length = ARRAY_SIZE(pac1921_int_num_samples);
return IIO_AVAIL_LIST;
+ case IIO_CHAN_INFO_SCALE:
+ switch (chan->channel) {
+ case PAC1921_CHAN_VBUS:
+ *vals = (const int *)pac1921_vbus_scales;
+ *length = ARRAY_SIZE(pac1921_vbus_scales) * 2;
+ *type = IIO_VAL_INT_PLUS_NANO;
+ return IIO_AVAIL_LIST;
+
+ case PAC1921_CHAN_VSENSE:
+ *vals = (const int *)pac1921_vsense_scales;
+ *length = ARRAY_SIZE(pac1921_vsense_scales) * 2;
+ *type = IIO_VAL_INT_PLUS_NANO;
+ return IIO_AVAIL_LIST;
+
+ case PAC1921_CHAN_CURRENT: {
+ struct pac1921_priv *priv = iio_priv(indio_dev);
+
+ *length = ARRAY_SIZE(priv->current_scales) * 2;
+ *type = IIO_VAL_INT_PLUS_NANO;
+
+ guard(mutex)(&priv->lock);
+
+ *vals = kmemdup_array((int *)priv->current_scales,
+ *length, sizeof(int), GFP_KERNEL);
+ if (!*vals)
+ return -ENOMEM;
+
+ return IIO_AVAIL_LIST;
+ }
+ default:
+ return -EINVAL;
+ }
default:
return -EINVAL;
}
}

+static void pac1921_read_avail_release_res(struct iio_dev *indio_dev,
+ struct iio_chan_spec const *chan,
+ const int *vals, long mask)
+{
+ if (mask == IIO_CHAN_INFO_SCALE &&
+ chan->channel == PAC1921_CHAN_CURRENT)
+ kfree(vals);
+}
+
/*
* Perform configuration update sequence: set the device into read state, then
* write the config register and set the device back into integration state.
@@ -748,6 +789,7 @@ static int pac1921_read_event_value(struct iio_dev *indio_dev,
static const struct iio_info pac1921_iio = {
.read_raw = pac1921_read_raw,
.read_avail = pac1921_read_avail,
+ .read_avail_release_resource = pac1921_read_avail_release_res,
.write_raw = pac1921_write_raw,
.write_raw_get_fmt = pac1921_write_raw_get_fmt,
.read_label = pac1921_read_label,
@@ -805,88 +847,7 @@ static ssize_t pac1921_write_shunt_resistor(struct iio_dev *indio_dev,
return len;
}

-/*
- * Emit on sysfs the list of available scales contained in scales_tbl
- *
- * TODO:: this function can be replaced with iio_format_avail_list() if the
- * latter will ever be exported.
- *
- * Must be called with lock held if the scales_tbl can change runtime (e.g. for
- * the current scales table)
- */
-static ssize_t pac1921_format_scale_avail(const int (*const scales_tbl)[2],
- size_t size, char *buf)
-{
- ssize_t len = 0;
-
- for (unsigned int i = 0; i < size; i++) {
- if (i != 0) {
- len += sysfs_emit_at(buf, len, " ");
- if (len >= PAGE_SIZE)
- return -EFBIG;
- }
- len += sysfs_emit_at(buf, len, "%d.%09d", scales_tbl[i][0],
- scales_tbl[i][1]);
- if (len >= PAGE_SIZE)
- return -EFBIG;
- }
-
- len += sysfs_emit_at(buf, len, "\n");
- return len;
-}
-
-/*
- * Read available scales for a specific channel
- *
- * NOTE: using extended info insted of iio.read_avail() because access to
- * current scales must be locked as they depend on shunt resistor which may
- * change runtime. Caller of iio.read_avail() would access the table unlocked
- * instead.
- */
-static ssize_t pac1921_read_scale_avail(struct iio_dev *indio_dev,
- uintptr_t private,
- const struct iio_chan_spec *chan,
- char *buf)
-{
- struct pac1921_priv *priv = iio_priv(indio_dev);
- const int (*scales_tbl)[2];
- size_t size;
-
- switch (chan->channel) {
- case PAC1921_CHAN_VBUS:
- scales_tbl = pac1921_vbus_scales;
- size = ARRAY_SIZE(pac1921_vbus_scales);
- return pac1921_format_scale_avail(scales_tbl, size, buf);
-
- case PAC1921_CHAN_VSENSE:
- scales_tbl = pac1921_vsense_scales;
- size = ARRAY_SIZE(pac1921_vsense_scales);
- return pac1921_format_scale_avail(scales_tbl, size, buf);
-
- case PAC1921_CHAN_CURRENT: {
- guard(mutex)(&priv->lock);
- scales_tbl = priv->current_scales;
- size = ARRAY_SIZE(priv->current_scales);
- return pac1921_format_scale_avail(scales_tbl, size, buf);
- }
- default:
- return -EINVAL;
- }
-}
-
-#define PAC1921_EXT_INFO_SCALE_AVAIL { \
- .name = "scale_available", \
- .read = pac1921_read_scale_avail, \
- .shared = IIO_SEPARATE, \
-}
-
-static const struct iio_chan_spec_ext_info pac1921_ext_info_voltage[] = {
- PAC1921_EXT_INFO_SCALE_AVAIL,
- {}
-};
-
static const struct iio_chan_spec_ext_info pac1921_ext_info_current[] = {
- PAC1921_EXT_INFO_SCALE_AVAIL,
{
.name = "shunt_resistor",
.read = pac1921_read_shunt_resistor,
@@ -910,6 +871,7 @@ static const struct iio_chan_spec pac1921_channels[] = {
.type = IIO_VOLTAGE,
.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
BIT(IIO_CHAN_INFO_SCALE),
+ .info_mask_separate_available = BIT(IIO_CHAN_INFO_SCALE),
.info_mask_shared_by_all =
BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO) |
BIT(IIO_CHAN_INFO_SAMP_FREQ),
@@ -927,12 +889,12 @@ static const struct iio_chan_spec pac1921_channels[] = {
.indexed = 1,
.event_spec = pac1921_overflow_event,
.num_event_specs = ARRAY_SIZE(pac1921_overflow_event),
- .ext_info = pac1921_ext_info_voltage,
},
{
.type = IIO_VOLTAGE,
.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
BIT(IIO_CHAN_INFO_SCALE),
+ .info_mask_separate_available = BIT(IIO_CHAN_INFO_SCALE),
.info_mask_shared_by_all =
BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO) |
BIT(IIO_CHAN_INFO_SAMP_FREQ),
@@ -950,12 +912,12 @@ static const struct iio_chan_spec pac1921_channels[] = {
.indexed = 1,
.event_spec = pac1921_overflow_event,
.num_event_specs = ARRAY_SIZE(pac1921_overflow_event),
- .ext_info = pac1921_ext_info_voltage,
},
{
.type = IIO_CURRENT,
.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
BIT(IIO_CHAN_INFO_SCALE),
+ .info_mask_separate_available = BIT(IIO_CHAN_INFO_SCALE),
.info_mask_shared_by_all =
BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO) |
BIT(IIO_CHAN_INFO_SAMP_FREQ),

--
2.47.0