linux-kernel - Re: [Linaro-mm-sig] [RFC v2 1/2] dma-buf: Introduce dma buffer sharing mechanism

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Message-ID: <20111209142405.6f371be6@pyramind.ukuu.org.uk>
Date:	Fri, 9 Dec 2011 14:24:05 +0000
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Daniel Vetter <daniel@...ll.ch>,
	"Semwal, Sumit" <sumit.semwal@...com>, linux@....linux.org.uk,
	linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
	linaro-mm-sig@...ts.linaro.org, linux-mm@...ck.org,
	linux-media@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [Linaro-mm-sig] [RFC v2 1/2] dma-buf: Introduce dma buffer
 sharing mechanism

> I still don't think that's possible. Please explain how you expect
> to change the semantics of the streaming mapping API to allow multiple
> mappers without having explicit serialization points that are visible
> to all users. For simplicity, let's assume a cache coherent system

I would agree. It's not just about barriers but in many cases where you
have multiple mappings by hardware devices the actual hardware interface
is specific to the devices. Just take a look at the fencing in TTM and
the graphics drivers.

Its not something the low level API can deal with, it requires high level
knowledge.

Alan
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