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Subject: Re: [PATCH v2] iio: adc: stm32-dfsdm: Use dma_request_chan() instead
 dma_request_slave_channel()
To:     Peter Ujfalusi <peter.ujfalusi@ti.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>
 <45195b31-70fa-39c9-e109-eeb33d6a2663@ti.com>
From:   Fabrice Gasnier <fabrice.gasnier@st.com>
Message-ID: <5328b668-2522-5d8d-83bb-f99bfe3086ed@st.com>
Date:   Thu, 9 Jan 2020 13:56:14 +0100
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On 1/9/20 12:40 PM, Peter Ujfalusi wrote:
> 
> 
> 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.

Oh yes, so please forget this.
Thanks,
Fabrice

> 
>>
>>>
>>>>
>>>> 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
>