linux-kernel - Re: [PATCH 3/3] dma_buf: Add documentation for the new cpu access support

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Message-ID: <CAKMK7uGnfN9TyK-53OPTQ2r609ZNZ6jcAYVhaSe_ywAaBOPJ6Q@mail.gmail.com>
Date:	Mon, 5 Mar 2012 22:39:05 +0100
From:	Daniel Vetter <daniel.vetter@...ll.ch>
To:	Sakari Ailus <sakari.ailus@....fi>
Cc:	linaro-mm-sig@...ts.linaro.org,
	LKML <linux-kernel@...r.kernel.org>,
	DRI Development <dri-devel@...ts.freedesktop.org>,
	linux-media@...r.kernel.org
Subject: Re: [PATCH 3/3] dma_buf: Add documentation for the new cpu access support

On Sat, Mar 3, 2012 at 01:23, Sakari Ailus <sakari.ailus@....fi> wrote:
> Where it should be decided which operations are being done to the buffer
> when it is passed to user space and back to kernel space?
>
> How about spliting these operations to those done on the first time the
> buffer is passed to the user space (mapping to kernel address space, for
> example) and those required every time buffer is passed from kernel to user
> and back (cache flusing)?
>
> I'm asking since any unnecessary time-consuming operations, especially as
> heavy as mapping the buffer, should be avoidable in subsystems dealing
> with streaming video, cameras etc., i.e. non-GPU users.

I'm a bit confused about your comments because this interface
extension doesn't support userspace mmap. So userspace isn't even part
of the picture. Adding mmap support is something entirely different
imo, and I have no idea yet how we should handle cache coherency for
that.

Yours, Daniel
-- 
Daniel Vetter
daniel.vetter@...ll.ch - +41 (0) 79 365 57 48 - http://blog.ffwll.ch
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