linux-kernel - Re: [PATCH v3 4/4] media: pxa_camera: conversion to dmaengine

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Message-ID: <87613w1sf5.fsf@belgarion.home>
Date:	Sun, 30 Aug 2015 21:34:54 +0200
From:	Robert Jarzmik <robert.jarzmik@...e.fr>
To:	Guennadi Liakhovetski <g.liakhovetski@....de>
Cc:	Mauro Carvalho Chehab <mchehab@....samsung.com>,
	Jiri Kosina <trivial@...nel.org>,
	Linux Media Mailing List <linux-media@...r.kernel.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 4/4] media: pxa_camera: conversion to dmaengine

Guennadi Liakhovetski <g.liakhovetski@....de> writes:

>> +	last_buf = list_entry(pcdev->capture.prev,
>> +			      struct pxa_buffer, vb.queue);
>
> You can use list_last_entry()
Ok.

>> +	last_status = dma_async_is_tx_complete(pcdev->dma_chans[chan],
>> +					       last_buf->cookie[chan],
>> +					       NULL, &last_issued);
>> +	if (camera_status & overrun &&
>> +	    last_status != DMA_COMPLETE) {
>> +		dev_dbg(dev, "FIFO overrun! CISR: %x\n",
>> +			camera_status);
>> +		pxa_camera_stop_capture(pcdev);
>> +		list_for_each_entry(buf, &pcdev->capture, vb.queue)
>> +			pxa_dma_add_tail_buf(pcdev, buf);
>
> Why have you added this loop? Is it a bug in the current implementation or 
> is it only needed with the switch to dmaengine?
It's a consequence of the switch.

With dmaengine, a dmaengine_terminate_all() removes all queued txs. It is
therefore necessary to requeue them. In the previous implementation, the
chaining was still good, and it was "enough" to just queue the first
videobuffer : the other buffers would follow by chaining.

Cheers.

-- 
Robert
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