linux-kernel - Re: [PATCH 2/2] V4L: mx3-camera: prepare to support multi-size buffers

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Date:	Fri, 26 Aug 2011 01:07:17 +0200 (CEST)
From:	Guennadi Liakhovetski <g.liakhovetski@....de>
To:	Laurent Pinchart <laurent.pinchart@...asonboard.com>
cc:	Linux Media Mailing List <linux-media@...r.kernel.org>,
	Hans Verkuil <hverkuil@...all.nl>,
	Pawel Osciak <pawel@...iak.com>,
	Sakari Ailus <sakari.ailus@...well.research.nokia.com>,
	Mauro Carvalho Chehab <mchehab@...radead.org>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Vinod Koul <vinod.koul@...el.com>,
	Dan Williams <dan.j.williams@...el.com>,
	Sascha Hauer <kernel@...gutronix.de>
Subject: Re: [PATCH 2/2] V4L: mx3-camera: prepare to support multi-size
 buffers

On Thu, 25 Aug 2011, Laurent Pinchart wrote:

> Hi Guennadi,
> 
> On Thursday 25 August 2011 18:46:03 Guennadi Liakhovetski wrote:
> > Prepare the mx3_camera friver to support the new VIDIOC_CREATE_BUFS and
> > VIDIOC_PREPARE_BUF ioctl()s. The .queue_setup() vb2 operation must be
> > able to handle buffer sizes, provided by the caller, and the
> > .buf_prepare() operation must not use the currently configured frame
> > format for its operation, which makes it superfluous for this driver.
> > Its functionality is moved into .buf_queue().
> 
> You're moving the ichan->dma_chan.device->device_prep_slave_sg() call from 
> .buf_prepare() to .buf_queue(). Is that call cheap ? Otherwise it would be 
> better to keep the .buf_prepare() callback.

But only if (buf->state == CSI_BUF_NEEDS_INIT), i.e., only on the first 
invocation. In any case, look at idmac_prep_slave_sg() - it is cheap. To 
do this in .buf_prepare I'd have to store the frame format from the 
.queue_setup() with a list of indices, to which it applies, and then use 
it in .buf_prepare()...

Thanks
Guennadi
---
Guennadi Liakhovetski, Ph.D.
Freelance Open-Source Software Developer
http://www.open-technology.de/
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