linux-kernel - Re: [Linaro-mm-sig] [RFC] ARM DMA mapping TODO, v1

Open Source and information security mailing list archives

Message-ID: <4DBAA9B4.3070306@vmware.com>
Date:	Fri, 29 Apr 2011 14:06:12 +0200
From:	Thomas Hellstrom <thellstrom@...are.com>
To:	Arnd Bergmann <arnd@...db.de>
CC:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	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 04/29/2011 01:26 PM, Arnd Bergmann wrote:
> On Thursday 28 April 2011, Benjamin Herrenschmidt wrote:
>    
>>>> For PCI you can have the flag propagate from the PHB down, for busses
>>>> without a bus type (platform) then whoever instanciate them (the
>>>> platform code) can set that appropriately.
>>>>          
>>> How can you do that when it changes mid-bus heirarchy?  I'm thinking
>>> of the situation where the DRM stuff is on a child bus below the
>>> root bus, and the root bus has DMA coherent devices on it but the DRM
>>> stuff doesn't.
>>>        
>> But that's not PCI right ? IE. with PCI, coherency is a property of the
>> PHB...
>>      
> That is my understanding at least, but I'd like to have a confirmation
> from the DRM folks.
>
> I believe that the PC graphics cards that have noncoherent DMA mappings
> are all of the unified memory (integrated into the northbridge) kind,
> so they are not on the same host bridge as all regular PCI devices,
> even if they appear as a PCI device.
>    

I think Jerome has mentioned at one point that the Radeon graphics cards 
support
non-coherent mappings.

Fwiw, the PowerVR SGX MMU also supports this mode of operation, although 
it being functional I guess depends on the system implementation.

/Thomas

> 	Arnd
>
> _______________________________________________
> Linaro-mm-sig mailing list
> Linaro-mm-sig@...ts.linaro.org
> http://lists.linaro.org/mailman/listinfo/linaro-mm-sig
>    

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