[PATCH 2/7] iio: pac1921: use read_avail+release APIs instead of custom ext_info

[Matteo Martelli]

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@xxxxxxxxx>
---
 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 4c2a1c07bc399028f0334885fc9cd4552d5892b1..f491a4923380ef9b406a68f8cc413df873869e3e 100644
--- a/drivers/iio/adc/pac1921.c
+++ b/drivers/iio/adc/pac1921.c
@@ -445,11 +445,52 @@ 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.
@@ -749,6 +790,7 @@ 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,
@@ -806,88 +848,7 @@ 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,
@@ -911,6 +872,7 @@ 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),
@@ -928,12 +890,12 @@ 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),
@@ -951,12 +913,12 @@ 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),

-- 
2.46.2