[PATCH v3 3/4] iio: adc: ltc2497: select the channel set per device

[Andrei Stancovici via B4 Relay]

From: Andrei Stancovici <andrei.stancovici@xxxxxxxxxx>

Ahead of adding a part with a different channel map, describe each
layout as a channel set in the core and let chip_info point at the one
its part uses. Probe takes the channel array and its length from there
instead of picking a table and trimming the count itself.

No functional change.

Signed-off-by: Andrei Stancovici <andrei.stancovici@xxxxxxxxxx>

---
Changes in v3:
- New patch. The channel-set mechanism is introduced before the LTC2493
  so that the patch adding the part does not change the chip_info of the
  parts already supported (Nuno Sá).
- chip_info references a channel set directly rather than carrying the
  single-ended input count for the core to match against a keyed table.
  That removes the probe-time search and its -EINVAL path. The count had
  no remaining user once the search was gone, so it is removed with it;
  the direct reference is what now carries the relationship the integer
  added in v2 was standing in for (Jonathan Cameron, Nuno Sá).
- pahole, struct ltc2497_chip_info, before -> after: LP64 16 -> 24
  bytes, ILP32 12 -> 16 bytes, no holes either way. The driver holds
  four of these, all static and const. The ILP32 figures were taken
  from a standalone build of the struct by the host compiler; no 32-bit
  kernel toolchain was available here.
- Verified as no functional change on hardware: the complete sysfs
  attribute tree of the LTC2497 and the LTC2499, names and values, is
  identical across this patch, and both parts still pass their full
  suites at this commit (LTC2499 36/36, LTC2497 24/24).
---
 drivers/iio/adc/ltc2496.c      |  1 +
 drivers/iio/adc/ltc2497-core.c | 27 ++++++++++++++++++---------
 drivers/iio/adc/ltc2497.c      |  2 ++
 drivers/iio/adc/ltc2497.h      | 13 +++++++++++++
 4 files changed, 34 insertions(+), 9 deletions(-)

diff --git a/drivers/iio/adc/ltc2496.c b/drivers/iio/adc/ltc2496.c
index 5b5b6ab28850..ffddd6368755 100644
--- a/drivers/iio/adc/ltc2496.c
+++ b/drivers/iio/adc/ltc2496.c
@@ -89,6 +89,7 @@ static void ltc2496_remove(struct spi_device *spi)
 static const struct ltc2497_chip_info ltc2496_info = {
 	.resolution = 16,
 	.name = NULL,
+	.channel_set = &ltc2497_chanset_ltc2497,
 };
 
 static const struct of_device_id ltc2496_of_match[] = {
diff --git a/drivers/iio/adc/ltc2497-core.c b/drivers/iio/adc/ltc2497-core.c
index c218d87d3a62..576a7c0a0f9b 100644
--- a/drivers/iio/adc/ltc2497-core.c
+++ b/drivers/iio/adc/ltc2497-core.c
@@ -420,6 +420,22 @@ static const struct iio_chan_spec _name[] = {                           \
 LTC2497_DEFINE_CHANNELS(ltc2497core_channel, 0);
 LTC2497_DEFINE_CHANNELS(ltc2497core_channel_samp_freq, BIT(IIO_CHAN_INFO_SAMP_FREQ));
 
+/*
+ * The temperature channel is the last entry of each table, so a part without
+ * the sensor stops one short of it.
+ */
+const struct ltc2497_channel_set ltc2497_chanset_ltc2497 = {
+	.channels	= ltc2497core_channel,
+	.num_channels	= ARRAY_SIZE(ltc2497core_channel) - 1,
+};
+EXPORT_SYMBOL_NS_GPL(ltc2497_chanset_ltc2497, "LTC2497");
+
+const struct ltc2497_channel_set ltc2497_chanset_ltc2499 = {
+	.channels	= ltc2497core_channel_samp_freq,
+	.num_channels	= ARRAY_SIZE(ltc2497core_channel_samp_freq),
+};
+EXPORT_SYMBOL_NS_GPL(ltc2497_chanset_ltc2499, "LTC2497");
+
 static const struct iio_info ltc2497core_info = {
 	.read_raw = ltc2497core_read_raw,
 	.read_avail = ltc2497core_read_avail,
@@ -443,15 +459,8 @@ int ltc2497core_probe(struct device *dev, struct iio_dev *indio_dev)
 
 	indio_dev->info = &ltc2497core_info;
 	indio_dev->modes = INDIO_DIRECT_MODE;
-	if (ddata->chip_info->has_speed_mode)
-		indio_dev->channels = ltc2497core_channel_samp_freq;
-	else
-		indio_dev->channels = ltc2497core_channel;
-	/* Only the ltc2499 has a temperature channel; it is the last entry. */
-	if (ddata->chip_info->has_temp)
-		indio_dev->num_channels = ARRAY_SIZE(ltc2497core_channel);
-	else
-		indio_dev->num_channels = ARRAY_SIZE(ltc2497core_channel) - 1;
+	indio_dev->channels = ddata->chip_info->channel_set->channels;
+	indio_dev->num_channels = ddata->chip_info->channel_set->num_channels;
 
 	if (ddata->chip_info->has_rejection_mode) {
 		struct iio_chan_spec *channels;
diff --git a/drivers/iio/adc/ltc2497.c b/drivers/iio/adc/ltc2497.c
index 4cccd3b7c8ef..984f15eb06f6 100644
--- a/drivers/iio/adc/ltc2497.c
+++ b/drivers/iio/adc/ltc2497.c
@@ -176,10 +176,12 @@ static const struct ltc2497_chip_info ltc2497_info[] = {
 	[TYPE_LTC2497] = {
 		.resolution = 16,
 		.name = NULL,
+		.channel_set = &ltc2497_chanset_ltc2497,
 	},
 	[TYPE_LTC2499] = {
 		.resolution = 24,
 		.name = "ltc2499",
+		.channel_set = &ltc2497_chanset_ltc2499,
 		.has_temp = true,
 		.has_speed_mode = true,
 		.has_rejection_mode = true,
diff --git a/drivers/iio/adc/ltc2497.h b/drivers/iio/adc/ltc2497.h
index 3a3fd82b21a3..7335c6c0af84 100644
--- a/drivers/iio/adc/ltc2497.h
+++ b/drivers/iio/adc/ltc2497.h
@@ -44,8 +44,21 @@ enum ltc2497_rejection {
 	LTC2499_REJECT_60,
 };
 
+/*
+ * The set of channels a part exposes.  Each supported channel layout has one
+ * of these in the core; a part names its own through chip_info.
+ */
+struct ltc2497_channel_set {
+	const struct iio_chan_spec	*channels;
+	unsigned int			num_channels;
+};
+
+extern const struct ltc2497_channel_set ltc2497_chanset_ltc2497;
+extern const struct ltc2497_channel_set ltc2497_chanset_ltc2499;
+
 struct ltc2497_chip_info {
 	const char *name;
+	const struct ltc2497_channel_set *channel_set;
 	u32 resolution;
 	bool has_temp;
 	bool has_speed_mode;	/* SPD bit in the 2nd config byte (LTC2499/LTC2493) */

-- 
2.43.0