linux-kernel - [PATCH] iio: adc: ad7124: add debugfs to disable single cycle mode

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Message-Id: <20250917-iio-adc-ad7124-add-debugfs-to-disable-single_cycle-v1-1-c83ab725faca@baylibre.com>
Date: Wed, 17 Sep 2025 18:03:17 -0500
From: David Lechner <dlechner@...libre.com>
To: Michael Hennerich <Michael.Hennerich@...log.com>, 
 Jonathan Cameron <jic23@...nel.org>, 
 Nuno Sá <nuno.sa@...log.com>, 
 Andy Shevchenko <andy@...nel.org>
Cc: linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org, 
 David Lechner <dlechner@...libre.com>
Subject: [PATCH] iio: adc: ad7124: add debugfs to disable single cycle mode

Add a boolean debugfs attribute to allow disabling the SINGLE_CYCLE
bit in the FILTER registers.

This causes data to be read on every conversion instead of doing the
usual 3 or 4 conversions per sample (depending on the filter). This is
only needed for very specific use cases, such as validating the
performance of the ADC. So we just expose this feature through debugfs
for the rare cases where it is needed by people who really know what
they are doing.

Signed-off-by: David Lechner <dlechner@...libre.com>
---
In a recent discussion with an engineer who has used these chips a lot,
we confirmed that we made the right choice in [1] about always enabling
the SINGLE_CYCLE bit. That is what is needed in normal operation and is
the expected behavior.

But there are some occasions where we might want to turn it off for
hardware debugging (e.g. to peer into what the filter on the ADC is
doing). Hence, this patch to add a debugfs entry to allow it.

FYI, there will be some trivial fuzz between this patch and the "iio:
adc: ad7124: change setup reg allocation strategy" patch, but I expect
changes to be requested on that one, so will likely work itself out
by the time it actually gets picked up.

[1]: https://lore.kernel.org/linux-iio/20250910-iio-adc-ad7124-fix-samp-freq-for-multi-channel-v4-1-8ca624c6114c@baylibre.com/
---
 drivers/iio/adc/ad7124.c | 25 +++++++++++++++++++++++--
 1 file changed, 23 insertions(+), 2 deletions(-)

diff --git a/drivers/iio/adc/ad7124.c b/drivers/iio/adc/ad7124.c
index 910b40393f77de84afc77d406c17c6e5051a02cd..ad6edbc792db35a644df37fce62bf95b79881455 100644
--- a/drivers/iio/adc/ad7124.c
+++ b/drivers/iio/adc/ad7124.c
@@ -10,6 +10,7 @@
 #include <linux/cleanup.h>
 #include <linux/clk.h>
 #include <linux/clk-provider.h>
+#include <linux/debugfs.h>
 #include <linux/delay.h>
 #include <linux/device.h>
 #include <linux/err.h>
@@ -223,6 +224,7 @@ struct ad7124_state {
 	 */
 	unsigned int gain_default;
 	DECLARE_KFIFO(live_cfgs_fifo, struct ad7124_channel_config *, AD7124_MAX_CONFIGS);
+	bool enable_single_cycle;
 };
 
 static const struct ad7124_chip_info ad7124_4_chip_info = {
@@ -560,13 +562,15 @@ static int ad7124_write_config(struct ad7124_state *st, struct ad7124_channel_co
 	 * sampling frequency even when only one channel is enabled in a
 	 * buffered read. If it was not set, the N in ad7124_set_channel_odr()
 	 * would be 1 and we would get a faster sampling frequency than what
-	 * was requested.
+	 * was requested. It may only be disabled through debugfs for testing
+	 * purposes.
 	 */
 	return ad_sd_write_reg(&st->sd, AD7124_FILTER(cfg->cfg_slot), 3,
 			       FIELD_PREP(AD7124_FILTER_FILTER, filter) |
 			       FIELD_PREP(AD7124_FILTER_REJ60, rej60) |
 			       FIELD_PREP(AD7124_FILTER_POST_FILTER, post) |
-			       AD7124_FILTER_SINGLE_CYCLE |
+			       FIELD_PREP(AD7124_FILTER_SINGLE_CYCLE,
+					  st->enable_single_cycle) |
 			       FIELD_PREP(AD7124_FILTER_FS, cfg->odr_sel_bits));
 }
 
@@ -1609,6 +1613,18 @@ static void ad7124_reg_disable(void *r)
 	regulator_disable(r);
 }
 
+static void ad7124_debugfs_init(struct iio_dev *indio_dev)
+{
+	struct dentry *dentry = iio_get_debugfs_dentry(indio_dev);
+	struct ad7124_state *st = iio_priv(indio_dev);
+
+	if (!IS_ENABLED(CONFIG_DEBUG_FS))
+		return;
+
+	debugfs_create_bool("enable_single_cycle", 0644, dentry,
+			    &st->enable_single_cycle);
+}
+
 static int ad7124_probe(struct spi_device *spi)
 {
 	const struct ad7124_chip_info *info;
@@ -1629,6 +1645,9 @@ static int ad7124_probe(struct spi_device *spi)
 
 	st->chip_info = info;
 
+	/* Only disabled for debug/testing purposes. */
+	st->enable_single_cycle = true;
+
 	indio_dev->name = st->chip_info->name;
 	indio_dev->modes = INDIO_DIRECT_MODE;
 	indio_dev->info = &ad7124_info;
@@ -1686,6 +1705,8 @@ static int ad7124_probe(struct spi_device *spi)
 	if (ret < 0)
 		return dev_err_probe(dev, ret, "Failed to register iio device\n");
 
+	ad7124_debugfs_init(indio_dev);
+
 	return 0;
 }
 

---
base-commit: 561285d048053fec8a3d6d1e3ddc60df11c393a0
change-id: 20250917-iio-adc-ad7124-add-debugfs-to-disable-single_cycle-c378ef330b89

Best regards,
-- 
David Lechner <dlechner@...libre.com>