[PATCH v3] iio: adc: ad4695: Fix call ordering in offload buffer postenable

[Radu Sabau via B4 Relay]

From: Radu Sabau <radu.sabau@xxxxxxxxxx>

ad4695_enter_advanced_sequencer_mode() was called after
spi_offload_trigger_enable(). That is wrong because
ad4695_enter_advanced_sequencer_mode() issues regular SPI transfers to
put the ADC into advanced sequencer mode, and not all SPI offload capable
controllers support regular SPI transfers while offloading is enabled.

Fix this by calling ad4695_enter_advanced_sequencer_mode() before
spi_offload_trigger_enable(), so the ADC is fully configured before the
first CNV pulse can occur. This is consistent with the same constraint
that already applies to the BUSY_GP_EN write above it.

Update the error unwind labels accordingly: add err_exit_conversion_mode
so that a failure of spi_offload_trigger_enable() correctly exits
conversion mode before clearing BUSY_GP_EN.

Fixes: f09f140e3ea8 ("iio: adc: ad4695: Add support for SPI offload")
Reviewed-by: Nuno Sá <nuno.sa@xxxxxxxxxx>
Reviewed-by: David Lechner <dlechner@xxxxxxxxxxxx>
Signed-off-by: Radu Sabau <radu.sabau@xxxxxxxxxx>
---
ad4695_enter_advanced_sequencer_mode() issues regular SPI transfers to
configure the ADC. These must complete before spi_offload_trigger_enable()
enables the PWM/CNV trigger, because once CNV pulses are live the offload
engine owns the SPI bus.

This fixes the call ordering and updates the error unwind path accordingly.
---
Changes in v3:
- Reword commit message: "the offload engine owns the SPI bus; any
  concurrent regular SPI transfer produces undefined behaviour" →
  "not all SPI offload capable controllers support regular SPI
  transfers while offloading is enabled".
- Rename err_trigger_disable → err_offload_trigger_disable to reduce
  diff churn.
- Link to v2: https://lore.kernel.org/r/20260401-ad4696-fix-v2-1-2480b9a30749@xxxxxxxxxx

Changes in v2:
- Reword commit message to explain the correct bus-ownership
  invariant directly, without reference to the HDL bug that
  exposed it.
- Remove unnecessary comment since the error path changed.
- Link to v1: https://lore.kernel.org/r/20260330-ad4696-fix-v1-1-e841e96451b2@xxxxxxxxxx
---
 drivers/iio/adc/ad4695.c | 23 ++++++++---------------
 1 file changed, 8 insertions(+), 15 deletions(-)

diff --git a/drivers/iio/adc/ad4695.c b/drivers/iio/adc/ad4695.c
index cda419638d9a..53642de7330d 100644
--- a/drivers/iio/adc/ad4695.c
+++ b/drivers/iio/adc/ad4695.c
@@ -876,14 +876,14 @@ static int ad4695_offload_buffer_postenable(struct iio_dev *indio_dev)
 	if (ret)
 		goto err_unoptimize_message;
 
-	ret = spi_offload_trigger_enable(st->offload, st->offload_trigger,
-					 &config);
+	ret = ad4695_enter_advanced_sequencer_mode(st, num_slots);
 	if (ret)
 		goto err_disable_busy_output;
 
-	ret = ad4695_enter_advanced_sequencer_mode(st, num_slots);
+	ret = spi_offload_trigger_enable(st->offload, st->offload_trigger,
+					 &config);
 	if (ret)
-		goto err_offload_trigger_disable;
+		goto err_exit_conversion_mode;
 
 	mutex_lock(&st->cnv_pwm_lock);
 	pwm_get_state(st->cnv_pwm, &state);
@@ -895,23 +895,16 @@ static int ad4695_offload_buffer_postenable(struct iio_dev *indio_dev)
 	ret = pwm_apply_might_sleep(st->cnv_pwm, &state);
 	mutex_unlock(&st->cnv_pwm_lock);
 	if (ret)
-		goto err_offload_exit_conversion_mode;
+		goto err_offload_trigger_disable;
 
 	return 0;
 
-err_offload_exit_conversion_mode:
-	/*
-	 * We have to unwind in a different order to avoid triggering offload.
-	 * ad4695_exit_conversion_mode() triggers a conversion, so it has to be
-	 * done after spi_offload_trigger_disable().
-	 */
-	spi_offload_trigger_disable(st->offload, st->offload_trigger);
-	ad4695_exit_conversion_mode(st);
-	goto err_disable_busy_output;
-
 err_offload_trigger_disable:
 	spi_offload_trigger_disable(st->offload, st->offload_trigger);
 
+err_exit_conversion_mode:
+	ad4695_exit_conversion_mode(st);
+
 err_disable_busy_output:
 	regmap_clear_bits(st->regmap, AD4695_REG_GP_MODE,
 			  AD4695_REG_GP_MODE_BUSY_GP_EN);

---
base-commit: 11439c4635edd669ae435eec308f4ab8a0804808
change-id: 20260330-ad4696-fix-186955a8c511

Best regards,
-- 
Radu Sabau <radu.sabau@xxxxxxxxxx>