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

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Date:   Fri, 10 Jan 2020 09:06:08 +0200
From:   Peter Ujfalusi <peter.ujfalusi@...com>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>
CC:     <mchehab@...nel.org>, <hyun.kwon@...inx.com>, <vkoul@...nel.org>,
        <linux-media@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <michal.simek@...inx.com>, <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] media: xilinx: Use dma_request_chan() instead
 dma_request_slave_channel()



On 09/01/2020 18.53, Laurent Pinchart wrote:
> Hello again,
> 
> On Thu, Jan 09, 2020 at 06:48:47PM +0200, Laurent Pinchart wrote:
>> On Tue, Dec 17, 2019 at 12:42:35PM +0200, 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>
>>
>> Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>
>>
>> Vinod, could you please pick this up ?
> 
> I spoke too fast.
> 
>>> ---
>>>  drivers/media/platform/xilinx/xilinx-dma.c | 6 +++---
>>>  1 file changed, 3 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/drivers/media/platform/xilinx/xilinx-dma.c b/drivers/media/platform/xilinx/xilinx-dma.c
>>> index b211380a11f2..9ce515ff9c0a 100644
>>> --- a/drivers/media/platform/xilinx/xilinx-dma.c
>>> +++ b/drivers/media/platform/xilinx/xilinx-dma.c
>>> @@ -725,10 +725,10 @@ int xvip_dma_init(struct xvip_composite_device *xdev, struct xvip_dma *dma,
>>>  
>>>  	/* ... and the DMA channel. */
>>>  	snprintf(name, sizeof(name), "port%u", port);
>>> -	dma->dma = dma_request_slave_channel(dma->xdev->dev, name);
>>> -	if (dma->dma == NULL) {
>>> +	dma->dma = dma_request_chan(dma->xdev->dev, name);
>>> +	if (IS_ERR(dma->dma)) {
>>>  		dev_err(dma->xdev->dev, "no VDMA channel found\n");

and print this only in case of !EPROBE_DEFER

>>> -		ret = -ENODEV;
>>> +		ret = PTR_ERR(dma->dma);
>>>  		goto error;
> 
> At the error label, we have
> 
> error:
> 	xvip_dma_cleanup(dma);
> 	return ret;
> 
> and xvip_dma_cleanup() contains
> 
> 	if (dma->dma)
> 		dma_release_channel(dma->dma);
> 
> You need to turn this into
> 
> 	if (!IS_ERR_OR_NULL(dma->dma))

I generally try to avoid IS_ERR_OR_NULL()

> 
> or add a
> 
> 		dma->dma = NULL;

But in this case I think it looks better that way.

> 
> in the error case in xvip_dma_init().
> 
>>>  	}
>>>  
> 

- Péter

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