Re: [RFC PATCH v2] dmabuf-sync: Introduce buffer synchronization framework

On Tue, Jun 18, 2013 at 06:04:44PM +0900, Inki Dae wrote:

quoted

-----Original Message-----
From: Russell King - ARM Linux [mailto:linux@arm.linux.org.uk]
Sent: Tuesday, June 18, 2013 5:43 PM
To: Inki Dae
Cc: 'Maarten Lankhorst'; 'linux-fbdev'; 'Kyungmin Park'; 'DRI mailing
list'; 'Rob Clark'; 'myungjoo.ham'; 'YoungJun Cho'; 'Daniel Vetter';
linux-arm-kernel@lists.infradead.org; linux-media@vger.kernel.org
Subject: Re: [RFC PATCH v2] dmabuf-sync: Introduce buffer synchronization
framework

On Tue, Jun 18, 2013 at 02:27:40PM +0900, Inki Dae wrote:

quoted

So I'd like to ask for other DRM maintainers. How do you think about it?

it

quoted

seems like that Intel DRM (maintained by Daniel), OMAP DRM (maintained

by

quoted

Rob) and GEM CMA helper also have same issue Russell pointed out. I

think

quoted

not only the above approach but also the performance is very important.

CMA uses coherent memory to back their buffers, though that might not be
true of memory obtained from other drivers via dma_buf.  Plus, there is
no support in the CMA helper for exporting or importng these buffers.

It's not so. Please see Dave's drm next. recently dmabuf support for the CMA
helper has been merged to there.

The point stands: CMA is DMA coherent memory.  It doesn't need and must
never be dma-map-sg'd or dma-sync'd or dma-unmap'd.