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Message-ID: <1304117620.2513.268.camel@pasglop>
Date: Sat, 30 Apr 2011 08:53:40 +1000
From: Benjamin Herrenschmidt <benh@...nel.crashing.org>
To: Thomas Hellstrom <thellstrom@...are.com>
Cc: Arnd Bergmann <arnd@...db.de>, linaro-mm-sig@...ts.linaro.org,
Russell King - ARM Linux <linux@....linux.org.uk>,
linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [Linaro-mm-sig] [RFC] ARM DMA mapping TODO, v1
On Fri, 2011-04-29 at 14:06 +0200, Thomas Hellstrom wrote:
> I think Jerome has mentioned at one point that the Radeon graphics
> cards support non-coherent mappings.
If the card is PCI/PCI-X/PCIe then coherency is not its business, it's
the business of the host bridge. However, on PCIe at least, the card can
indeed set a "no snoop" attribute on DMA transactions to request "no
coherency". At least the systems have the latitude to just ignore that
bit (like we do on all ppc afaik) :-)
> Fwiw, the PowerVR SGX MMU also supports this mode of operation,
> although it being functional I guess depends on the system
> implementation.
Right, it's not a GPU thing, it's really a system design thing.
Cheers,
Ben.
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