[PATCH v5 1/2] iio: adc: ad_sigma_delta: fix CS held asserted and state leaks

[Radu Sabau via B4 Relay <devnull+radu.sabau.analog.com@kernel.org>]

From: Radu Sabau <radu.sabau@analog.com>

In ad_sigma_delta_single_conversion(), set_mode(AD_SD_MODE_IDLE) and
disable_one() were called from the out: block while keep_cs_asserted
was still true. This caused any SPI transfer issued by those callbacks
to carry cs_change=1, leaving CS permanently asserted after the
conversion. Fix by moving both calls into the out_unlock: block, after
keep_cs_asserted is cleared, matching the pattern already used in
ad_sd_calibrate().

In the error path of ad_sd_buffer_postenable(), if an operation fails
after set_mode(AD_SD_MODE_CONTINUOUS) has already succeeded (e.g.
spi_offload_trigger_enable()), the device is left in continuous
conversion mode with CS physically asserted. Additionally,
bus_locked remaining true after spi_bus_unlock() causes subsequent
SPI operations to call spi_sync_locked() without the bus lock actually
held, allowing concurrent SPI access.

Fix the error path by clearing keep_cs_asserted first, then calling
set_mode(AD_SD_MODE_IDLE) to revert the device mode and deassert CS,
then clearing bus_locked before releasing the bus.

For devices that implement neither set_mode nor disable_one (such as
MAX11205, which has no physical CS pin), no SPI transfer is issued
during cleanup and the cs_change flag has no effect on any physical
line.

Signed-off-by: Radu Sabau <radu.sabau@analog.com>
---
 drivers/iio/adc/ad_sigma_delta.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/iio/adc/ad_sigma_delta.c b/drivers/iio/adc/ad_sigma_delta.c
index a955556f9ec8..651ade67ad2e 100644
--- a/drivers/iio/adc/ad_sigma_delta.c
+++ b/drivers/iio/adc/ad_sigma_delta.c
@@ -441,11 +441,10 @@ int ad_sigma_delta_single_conversion(struct iio_dev *indio_dev,
 out:
 	ad_sd_disable_irq(sigma_delta);
 
-	ad_sigma_delta_set_mode(sigma_delta, AD_SD_MODE_IDLE);
-	ad_sigma_delta_disable_one(sigma_delta, chan->address);
-
 out_unlock:
 	sigma_delta->keep_cs_asserted = false;
+	ad_sigma_delta_set_mode(sigma_delta, AD_SD_MODE_IDLE);
+	ad_sigma_delta_disable_one(sigma_delta, chan->address);
 	sigma_delta->bus_locked = false;
 	spi_bus_unlock(sigma_delta->spi->controller);
 out_release:
@@ -578,6 +577,9 @@ static int ad_sd_buffer_postenable(struct iio_dev *indio_dev)
 	return 0;
 
 err_unlock:
+	sigma_delta->keep_cs_asserted = false;
+	ad_sigma_delta_set_mode(sigma_delta, AD_SD_MODE_IDLE);
+	sigma_delta->bus_locked = false;
 	spi_bus_unlock(sigma_delta->spi->controller);
 	spi_unoptimize_message(&sigma_delta->sample_msg);
 

-- 
2.43.0