iio: ad_sigma_delta: Don't put SPI transfer buffer on the stack

Use a heap allocated memory for the SPI transfer buffer. Using stack memory
can corrupt stack memory when using DMA on some systems.

This change moves the buffer from the stack of the trigger handler call to
the heap of the buffer of the state struct. The size increases takes into
account the alignment for the timestamp, which is 8 bytes.

The 'data' buffer is split into 'tx_buf' and 'rx_buf', to make a clearer
separation of which part of the buffer should be used for TX & RX.

Fixes: af3008485ea03 ("iio:adc: Add common code for ADI Sigma Delta devices")
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Link: https://lore.kernel.org/r/20201124123807.19717-1-alexandru.ardelean@analog.com
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

diff --git a/drivers/iio/adc/ad_sigma_delta.c b/drivers/iio/adc/ad_sigma_delta.c
index 86039e9ecaca1b46aca1a57402403e36bf0985ba..3a6f239d4acca345fe3984421a26867d6defca06 100644 (file)
--- a/drivers/iio/adc/ad_sigma_delta.c
+++ b/drivers/iio/adc/ad_sigma_delta.c
@@ -57,7 +57,7 @@ EXPORT_SYMBOL_GPL(ad_sd_set_comm);
 int ad_sd_write_reg(struct ad_sigma_delta *sigma_delta, unsigned int reg,
        unsigned int size, unsigned int val)
 {
-       uint8_t *data = sigma_delta->data;
+       uint8_t *data = sigma_delta->tx_buf;
        struct spi_transfer t = {
                .tx_buf         = data,
                .len            = size + 1,
@@ -99,7 +99,7 @@ EXPORT_SYMBOL_GPL(ad_sd_write_reg);
 static int ad_sd_read_reg_raw(struct ad_sigma_delta *sigma_delta,
        unsigned int reg, unsigned int size, uint8_t *val)
 {
-       uint8_t *data = sigma_delta->data;
+       uint8_t *data = sigma_delta->tx_buf;
        int ret;
        struct spi_transfer t[] = {
                {
@@ -146,22 +146,22 @@ int ad_sd_read_reg(struct ad_sigma_delta *sigma_delta,
 {
        int ret;
 
-       ret = ad_sd_read_reg_raw(sigma_delta, reg, size, sigma_delta->data);
+       ret = ad_sd_read_reg_raw(sigma_delta, reg, size, sigma_delta->rx_buf);
        if (ret < 0)
                goto out;
 
        switch (size) {
        case 4:
-               *val = get_unaligned_be32(sigma_delta->data);
+               *val = get_unaligned_be32(sigma_delta->rx_buf);
                break;
        case 3:
-               *val = get_unaligned_be24(&sigma_delta->data[0]);
+               *val = get_unaligned_be24(sigma_delta->rx_buf);
                break;
        case 2:
-               *val = get_unaligned_be16(sigma_delta->data);
+               *val = get_unaligned_be16(sigma_delta->rx_buf);
                break;
        case 1:
-               *val = sigma_delta->data[0];
+               *val = sigma_delta->rx_buf[0];
                break;
        default:
                ret = -EINVAL;
@@ -395,11 +395,9 @@ static irqreturn_t ad_sd_trigger_handler(int irq, void *p)
        struct iio_poll_func *pf = p;
        struct iio_dev *indio_dev = pf->indio_dev;
        struct ad_sigma_delta *sigma_delta = iio_device_get_drvdata(indio_dev);
+       uint8_t *data = sigma_delta->rx_buf;
        unsigned int reg_size;
        unsigned int data_reg;
-       uint8_t data[16];
-
-       memset(data, 0x00, 16);
 
        reg_size = indio_dev->channels[0].scan_type.realbits +
                        indio_dev->channels[0].scan_type.shift;

diff --git a/include/linux/iio/adc/ad_sigma_delta.h b/include/linux/iio/adc/ad_sigma_delta.h
index a3a838dcf8e4a073da304d48df35de26700334e6..7199280d89ca483af4272106f0eaee29fa516482 100644 (file)
--- a/include/linux/iio/adc/ad_sigma_delta.h
+++ b/include/linux/iio/adc/ad_sigma_delta.h
@@ -79,8 +79,12 @@ struct ad_sigma_delta {
        /*
         * DMA (thus cache coherency maintenance) requires the
         * transfer buffers to live in their own cache lines.
+        * 'tx_buf' is up to 32 bits.
+        * 'rx_buf' is up to 32 bits per sample + 64 bit timestamp,
+        * rounded to 16 bytes to take into account padding.
         */
-       uint8_t                         data[4] ____cacheline_aligned;
+       uint8_t                         tx_buf[4] ____cacheline_aligned;
+       uint8_t                         rx_buf[16] __aligned(8);
 };
 
 static inline int ad_sigma_delta_set_channel(struct ad_sigma_delta *sd,