iio: adc: ad7606_spi: add offload scan mask check

Validate the scan mask when SPI offloading is being used.

Since this family of ADCs is simultaneous sampling, there isn't a way
to selectively disable channels when reading sample data. (Technically,
AD7616 has a sequencer so the driver could have some control, but that
is for another day).

For "regular" IIO triggered buffer reads, this isn't a problem and the
IIO core will demux the data and ignore data from disabled channels.
However, since SPI offloading is done completely in hardware, we don't
have a way to do the same. So before this patch, if less than all
channels were enabled, the data would be misplaced in the buffer.

By adding a check in update_scan_mode, we can fail to enable the buffer
instead of having bad data returned to userspace.

Fixes: e96d35faf357 ("iio: adc: ad7606: add SPI offload support")
Signed-off-by: David Lechner <dlechner@baylibre.com>
Reviewed-by: Andy Shevchenko <andy@kernel.org>
Reviewed-by: Nuno Sá <nuno.sa@analog.com>
Link: https://patch.msgid.link/20250502-iio-adc-ad7606_spi-fix-offload-scan-mask-check-v2-1-e70c6d71baa3@baylibre.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

diff --git a/drivers/iio/adc/ad7606_spi.c b/drivers/iio/adc/ad7606_spi.c
index 997be483ebb93293481b922e13ece4edb47e940a..5b5b4677273b15956f1da73da41b16c5ee64e818 100644 (file)
--- a/drivers/iio/adc/ad7606_spi.c
+++ b/drivers/iio/adc/ad7606_spi.c
@@ -5,6 +5,7 @@
  * Copyright 2011 Analog Devices Inc.
  */
 
+#include <linux/bitmap.h>
 #include <linux/err.h>
 #include <linux/math.h>
 #include <linux/module.h>
@@ -329,19 +330,44 @@ static int ad7606_spi_offload_probe(struct device *dev,
        return 0;
 }
 
+static int ad7606_spi_update_scan_mode(struct iio_dev *indio_dev,
+                                      const unsigned long *scan_mask)
+{
+       struct ad7606_state *st = iio_priv(indio_dev);
+
+       if (st->offload_en) {
+               unsigned int num_adc_ch = st->chip_info->num_adc_channels;
+
+               /*
+                * SPI offload requires that all channels are enabled since
+                * there isn't a way to selectively disable channels that get
+                * read (this is simultaneous sampling ADC) and the DMA buffer
+                * has no way of demuxing the data to filter out unwanted
+                * channels.
+                */
+               if (bitmap_weight(scan_mask, num_adc_ch) != num_adc_ch)
+                       return -EINVAL;
+       }
+
+       return 0;
+}
+
 static const struct ad7606_bus_ops ad7606_spi_bops = {
        .offload_config = ad7606_spi_offload_probe,
        .read_block = ad7606_spi_read_block,
+       .update_scan_mode = ad7606_spi_update_scan_mode,
 };
 
 static const struct ad7606_bus_ops ad7607_spi_bops = {
        .offload_config = ad7606_spi_offload_probe,
        .read_block = ad7606_spi_read_block14to16,
+       .update_scan_mode = ad7606_spi_update_scan_mode,
 };
 
 static const struct ad7606_bus_ops ad7608_spi_bops = {
        .offload_config = ad7606_spi_offload_probe,
        .read_block = ad7606_spi_read_block18to32,
+       .update_scan_mode = ad7606_spi_update_scan_mode,
 };
 
 static const struct ad7606_bus_ops ad7616_spi_bops = {
@@ -350,6 +376,7 @@ static const struct ad7606_bus_ops ad7616_spi_bops = {
        .reg_read = ad7606_spi_reg_read,
        .reg_write = ad7606_spi_reg_write,
        .rd_wr_cmd = ad7616_spi_rd_wr_cmd,
+       .update_scan_mode = ad7606_spi_update_scan_mode,
 };
 
 static const struct ad7606_bus_ops ad7606b_spi_bops = {
@@ -359,6 +386,7 @@ static const struct ad7606_bus_ops ad7606b_spi_bops = {
        .reg_write = ad7606_spi_reg_write,
        .rd_wr_cmd = ad7606b_spi_rd_wr_cmd,
        .sw_mode_config = ad7606b_sw_mode_config,
+       .update_scan_mode = ad7606_spi_update_scan_mode,
 };
 
 static const struct ad7606_bus_ops ad7606c_18_spi_bops = {
@@ -368,6 +396,7 @@ static const struct ad7606_bus_ops ad7606c_18_spi_bops = {
        .reg_write = ad7606_spi_reg_write,
        .rd_wr_cmd = ad7606b_spi_rd_wr_cmd,
        .sw_mode_config = ad7606b_sw_mode_config,
+       .update_scan_mode = ad7606_spi_update_scan_mode,
 };
 
 static const struct ad7606_bus_info ad7605_4_bus_info = {