linux-kernel - Re: [PATCH] media: stm32-dcmi: Use dma_request_chan() instead dma_request_slave

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Message-ID: <8229c7ed-b513-6bf8-5684-60d87a92d41f@st.com>
Date:   Tue, 7 Jan 2020 09:46:40 +0000
From:   Hugues FRUCHET <hugues.fruchet@...com>
To:     Peter Ujfalusi <peter.ujfalusi@...com>,
        "mchehab@...nel.org" <mchehab@...nel.org>,
        "mcoquelin.stm32@...il.com" <mcoquelin.stm32@...il.com>,
        Alexandre TORGUE <alexandre.torgue@...com>
CC:     "vkoul@...nel.org" <vkoul@...nel.org>,
        "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-stm32@...md-mailman.stormreply.com" 
        <linux-stm32@...md-mailman.stormreply.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] media: stm32-dcmi: Use dma_request_chan() instead
 dma_request_slave_channel()

Hi Peter,

If not too late, could you change trace to only trig error trace when
error is not "probe defered" ? See below:

-	chan = dma_request_slave_channel(&pdev->dev, "tx");
-	if (!chan) {
-		dev_info(&pdev->dev, "Unable to request DMA channel, defer probing\n");
-		return -EPROBE_DEFER;
+	chan = dma_request_chan(&pdev->dev, "tx");
+	if (IS_ERR(chan)) {
+		if (PTR_ERR(chan) != -EPROBE_DEFER)
+			dev_err(&pdev->dev, "Unable to request DMA channel\n");
+		return PTR_ERR(chan);


Best regards,
Hugues.

On 12/18/19 11:52 AM, Hugues FRUCHET wrote:
> Thanks for patching Peter,
> 
> No regression observed on my side.
> 
> Acked-by: Hugues Fruchet <hugues.fruchet@...com>
> 
> Best regards,
> Hugues.
> 
> On 12/17/19 11:41 AM, 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@...com>
>> ---
>>   drivers/media/platform/stm32/stm32-dcmi.c | 6 +++---
>>   1 file changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/media/platform/stm32/stm32-dcmi.c 
>> b/drivers/media/platform/stm32/stm32-dcmi.c
>> index 9392e3409fba..55351872b0c7 100644
>> --- a/drivers/media/platform/stm32/stm32-dcmi.c
>> +++ b/drivers/media/platform/stm32/stm32-dcmi.c
>> @@ -1910,10 +1910,10 @@ static int dcmi_probe(struct platform_device 
>> *pdev)
>>           return PTR_ERR(mclk);
>>       }
>> -    chan = dma_request_slave_channel(&pdev->dev, "tx");
>> -    if (!chan) {
>> +    chan = dma_request_chan(&pdev->dev, "tx");
>> +    if (IS_ERR(chan)) {
>>           dev_info(&pdev->dev, "Unable to request DMA channel, defer 
>> probing\n");
>> -        return -EPROBE_DEFER;
>> +        return PTR_ERR(chan);
>>       }
>>       spin_lock_init(&dcmi->irqlock);
>>