Re: [PATCH v2] iio: adc: stm32-dfsdm: Use dma_request_chan() instead dma_request_slave_channel()

On 09/01/2020 13.29, Fabrice Gasnier wrote:

On 1/9/20 11:32 AM, Peter Ujfalusi wrote:

quoted

On 09/01/2020 11.13, Fabrice Gasnier wrote:

quoted

On 1/7/20 12:45 PM, Peter Ujfalusi wrote:

quoted

dma_request_slave_channel() is a wrapper on top of dma_request_chan()
eating up the error code.

By using dma_request_chan() directly the driver can support deferred
probing against DMA.

Signed-off-by: Peter Ujfalusi <redacted>
---
Hi,

Changes since v1:
- Fall back to IRQ mode for ADC only in case of ENODEV

Hi Peter,

Thanks for the patch,

Please find a minor comment here after. Apart from that, you can add my:

Acked-by: Fabrice Gasnier <redacted>

quoted

Regards,
Peter

 drivers/iio/adc/stm32-dfsdm-adc.c | 21 +++++++++++++++++----
 1 file changed, 17 insertions(+), 4 deletions(-)

diff --git a/drivers/iio/adc/stm32-dfsdm-adc.c b/drivers/iio/adc/stm32-dfsdm-adc.c
index e493242c266e..74a2211bdff4 100644
--- a/drivers/iio/adc/stm32-dfsdm-adc.c
+++ b/drivers/iio/adc/stm32-dfsdm-adc.c

@@ -1383,9 +1383,13 @@ static int stm32_dfsdm_dma_request(struct iio_dev *indio_dev)
 {
 	struct stm32_dfsdm_adc *adc = iio_priv(indio_dev);
 
-	adc->dma_chan = dma_request_slave_channel(&indio_dev->dev, "rx");
-	if (!adc->dma_chan)
-		return -EINVAL;
+	adc->dma_chan = dma_request_chan(&indio_dev->dev, "rx");
+	if (IS_ERR(adc->dma_chan)) {
+		int ret = PTR_ERR(adc->dma_chan);
+
+		adc->dma_chan = NULL;
+		return ret;

You may "return PTR_ERR(adc->dma_chan);" directly here.

I don't make decision here on behalf of the adc path on to go forward w/
or w/o DMA support and if we go ahead the stm32_dfsdm_dma_release()
needs the dma_chan to be NULL in case we don't use DMA.

It is much cleaner to set dma_chan to NULL here than doing it in other
paths.

Hi Peter,

Hi Fabrice,

Sorry I wasn't clear enough. I agree with you. I was suggesting only,
talking about the 'ret' variable. It may be removed to spare a few lines
:-).
	if (IS_ERR(adc->dma_chan)) {
		adc->dma_chan = NULL;
		return PTR_ERR(adc->dma_chan);
	}
I'm okay both ways.

PTR_ERR(NULL); will return 0
I need to retrieve the actual error code before NULLing dma_chan.

quoted

quoted

Best Regards,
Fabrice

quoted

+	}
 
 	adc->rx_buf = dma_alloc_coherent(adc->dma_chan->device->dev,
 					 DFSDM_DMA_BUFFER_SIZE,

@@ -1509,7 +1513,16 @@ static int stm32_dfsdm_adc_init(struct iio_dev *indio_dev)
 	init_completion(&adc->completion);
 
 	/* Optionally request DMA */
-	if (stm32_dfsdm_dma_request(indio_dev)) {
+	ret = stm32_dfsdm_dma_request(indio_dev);
+	if (ret) {
+		if (ret != -ENODEV) {
+			if (ret != -EPROBE_DEFER)
+				dev_err(&indio_dev->dev,
+					"DMA channel request failed with %d\n",
+					ret);
+			return ret;
+		}
+
 		dev_dbg(&indio_dev->dev, "No DMA support\n");
 		return 0;
 	}

- Péter

Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki.
Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki

- Péter

Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki.
Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki

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