[PATCH] iio: adc: stm32-adc: enable timestamping for non-DMA usage

[Ahmad Fatoum]

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 <h...@pengutronix.de>
Signed-off-by: Ahmad Fatoum <a.fat...@pengutronix.de>
---
 drivers/iio/adc/stm32-adc.c | 31 +++++++++++++++++++++++++------
 1 file changed, 25 insertions(+), 6 deletions(-)

diff --git a/drivers/iio/adc/stm32-adc.c b/drivers/iio/adc/stm32-adc.c
index c067c994dae2..91d9483e1f5f 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 +1948,18 @@ 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) {
                handler = &stm32_adc_trigger_handler;
+               timestamping = true;
+       }
+
+       ret = stm32_adc_chan_of_init(indio_dev, timestamping);
+       if (ret < 0)
+               return ret;
 
        ret = iio_triggered_buffer_setup(indio_dev,
                                         &iio_pollfunc_store_time, handler,
-- 
2.30.0