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    Subject[PATCH v2] iio: adc: stm32-adc: enable timestamping for non-DMA usage
    Date
    For non-DMA usage, we have an easy way to associate a timestamp with a
    sample: iio_pollfunc_store_time stores a timestamp in the primary
    trigger IRQ handler and stm32_adc_trigger_handler runs in the IRQ thread
    to push out the buffer along with the timestamp.

    For this to work, the driver needs to register an IIO_TIMESTAMP channel.
    Do this.

    For DMA, it's not as easy, because we don't push the buffers out of
    stm32_adc_trigger, but out of stm32_adc_dma_buffer_done, which runs in
    a tasklet scheduled after a DMA completion.

    Preferably, the DMA controller would copy us the timestamp into that buffer
    as well. Until this is implemented, restrict timestamping support to
    only PIO. For low-frequency sampling, PIO is probably good enough.

    Cc: Holger Assmann <has@pengutronix.de>
    Acked-by: Fabrice Gasnier <fabrice.gasnier@foss.st.com>
    Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
    ---
    v1 -> v2:
    - Added comment about timestamping being PIO only (Fabrice)
    - Added missing DMA resource clean up in error path (Fabrice)
    - Added Fabrice's Acked-by
    ---
    drivers/iio/adc/stm32-adc.c | 35 +++++++++++++++++++++++++++++------
    1 file changed, 29 insertions(+), 6 deletions(-)

    diff --git a/drivers/iio/adc/stm32-adc.c b/drivers/iio/adc/stm32-adc.c
    index c067c994dae2..885bb514503c 100644
    --- a/drivers/iio/adc/stm32-adc.c
    +++ b/drivers/iio/adc/stm32-adc.c
    @@ -1718,7 +1718,7 @@ static void stm32_adc_chan_init_one(struct iio_dev *indio_dev,
    }
    }

    -static int stm32_adc_chan_of_init(struct iio_dev *indio_dev)
    +static int stm32_adc_chan_of_init(struct iio_dev *indio_dev, bool timestamping)
    {
    struct device_node *node = indio_dev->dev.of_node;
    struct stm32_adc *adc = iio_priv(indio_dev);
    @@ -1766,6 +1766,9 @@ static int stm32_adc_chan_of_init(struct iio_dev *indio_dev)
    return -EINVAL;
    }

    + if (timestamping)
    + num_channels++;
    +
    channels = devm_kcalloc(&indio_dev->dev, num_channels,
    sizeof(struct iio_chan_spec), GFP_KERNEL);
    if (!channels)
    @@ -1816,6 +1819,19 @@ static int stm32_adc_chan_of_init(struct iio_dev *indio_dev)
    stm32_adc_smpr_init(adc, channels[i].channel, smp);
    }

    + if (timestamping) {
    + struct iio_chan_spec *timestamp = &channels[scan_index];
    +
    + timestamp->type = IIO_TIMESTAMP;
    + timestamp->channel = -1;
    + timestamp->scan_index = scan_index;
    + timestamp->scan_type.sign = 's';
    + timestamp->scan_type.realbits = 64;
    + timestamp->scan_type.storagebits = 64;
    +
    + scan_index++;
    + }
    +
    indio_dev->num_channels = scan_index;
    indio_dev->channels = channels;

    @@ -1875,6 +1891,7 @@ static int stm32_adc_probe(struct platform_device *pdev)
    struct device *dev = &pdev->dev;
    irqreturn_t (*handler)(int irq, void *p) = NULL;
    struct stm32_adc *adc;
    + bool timestamping = false;
    int ret;

    if (!pdev->dev.of_node)
    @@ -1931,16 +1948,22 @@ static int stm32_adc_probe(struct platform_device *pdev)
    if (ret < 0)
    return ret;

    - ret = stm32_adc_chan_of_init(indio_dev);
    - if (ret < 0)
    - return ret;
    -
    ret = stm32_adc_dma_request(dev, indio_dev);
    if (ret < 0)
    return ret;

    - if (!adc->dma_chan)
    + if (!adc->dma_chan) {
    + /* For PIO mode only, iio_pollfunc_store_time stores a timestamp
    + * in the primary trigger IRQ handler and stm32_adc_trigger_handler
    + * runs in the IRQ thread to push out buffer along with timestamp.
    + */
    handler = &stm32_adc_trigger_handler;
    + timestamping = true;
    + }
    +
    + ret = stm32_adc_chan_of_init(indio_dev, timestamping);
    + if (ret < 0)
    + goto err_dma_disable;

    ret = iio_triggered_buffer_setup(indio_dev,
    &iio_pollfunc_store_time, handler,
    --
    2.30.0
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