linux-kernel - Re: [PATCH v3] [media] vb2: Add support for capture_dma

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Date:   Fri, 21 Oct 2016 10:53:22 +0200
From:   Thierry Escande <thierry.escande@...labora.com>
To:     Sakari Ailus <sakari.ailus@....fi>
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        Pawel Osciak <pawel@...iak.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Kyungmin Park <kyungmin.park@...sung.com>
Subject: Re: [PATCH v3] [media] vb2: Add support for capture_dma_bidirectional
 queue flag

Hi Sakari,

On 21/10/2016 09:48, Sakari Ailus wrote:
> Hi Thierry,
>
> On Fri, Oct 21, 2016 at 09:25:05AM +0200, Thierry Escande wrote:
>> From: Pawel Osciak <posciak@...omium.org>
>>
>> When this flag is set for CAPTURE queues by the driver on calling
>> vb2_queue_init(), it forces the buffers on the queue to be
>> allocated/mapped with DMA_BIDIRECTIONAL direction flag instead of
>> DMA_FROM_DEVICE. This allows the device not only to write to the
>> buffers, but also read out from them. This may be useful e.g. for codec
>> hardware which may be using CAPTURE buffers as reference to decode
>> other buffers.
>>
>> This flag is ignored for OUTPUT queues as we don't want to allow HW to
>> be able to write to OUTPUT buffers.
>>
>> Signed-off-by: Pawel Osciak <posciak@...omium.org>
>> Tested-by: Pawel Osciak <posciak@...omium.org>
>> Signed-off-by: Thierry Escande <thierry.escande@...labora.com>
>>
>
> Please also check where dma_dir is being used especially in memory type
> implementation. There are several comparisons to DMA_FROM_DEVICE which will
> have a different result if DMA_BIDIRECTIONAL is used instead.
Nice catch, thanks.

How about a macro like this:

#define VB2_DMA_DIR_CAPTURE(d) \
		((d) == DMA_FROM_DEVICE || (d) == DMA_BIDIRECTIONAL)

Regards,
  Thierry