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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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