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Subject: Re: [PATCH v2] iio: adc: stm32-dfsdm: Use dma_request_chan() instead
 dma_request_slave_channel()
To:     Fabrice Gasnier <fabrice.gasnier@st.com>, <jic23@kernel.org>,
        <mcoquelin.stm32@gmail.com>, <alexandre.torgue@st.com>
CC:     <vkoul@kernel.org>, <linux-iio@vger.kernel.org>,
        <linux-arm-kernel@lists.infradead.org>,
        <linux-kernel@vger.kernel.org>,
        <linux-stm32@st-md-mailman.stormreply.com>,
        Olivier MOYSAN <olivier.moysan@st.com>
References: <20200107114532.6697-1-peter.ujfalusi@ti.com>
 <eade6657-8470-0d70-b3c1-fcdddf891c6c@st.com>
 <4c0b7e3e-cd98-860a-e931-c216f1bc6e7a@ti.com>
 <698d9dec-4486-f70a-b8e0-dfd6b4bb907f@st.com>
From:   Peter Ujfalusi <peter.ujfalusi@ti.com>
Message-ID: <45195b31-70fa-39c9-e109-eeb33d6a2663@ti.com>
Date:   Thu, 9 Jan 2020 13:40:38 +0200
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On 09/01/2020 13.29, Fabrice Gasnier wrote:
> On 1/9/20 11:32 AM, Peter Ujfalusi wrote:
>>
>>
>> On 09/01/2020 11.13, Fabrice Gasnier wrote:
>>> On 1/7/20 12:45 PM, Peter Ujfalusi wrote:
>>>> 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 <peter.ujfalusi@ti.com>
>>>> ---
>>>> 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 <fabrice.gasnier@st.com>
>>>
>>>
>>>>
>>>> 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.

> 
>>
>>>
>>> Best Regards,
>>> Fabrice
>>>
>>>> +	}
>>>>  
>>>>  	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