linux-kernel - Re: [PATCH 1/2] arm: msm: Add System MMU support.

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Message-ID: <20100804095237.GH18307@amd.com>
Date:	Wed, 4 Aug 2010 11:52:37 +0200
From:	"Roedel, Joerg" <Joerg.Roedel@....com>
To:	Stepan Moskovchenko <stepanm@...eaurora.org>
CC:	Zach Pfeffer <zpfeffer@...eaurora.org>,
	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
	"arnd@...db.de" <arnd@...db.de>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
	"dwalker@...eaurora.org" <dwalker@...eaurora.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] arm: msm: Add System MMU support.

On Tue, Aug 03, 2010 at 02:43:20PM -0400, Stepan Moskovchenko wrote:
>   On 8/3/2010 2:23 AM, Roedel, Joerg wrote:
> > A domain is defined by a single page-table which can be modified using
> > the iommu_map/iommu_unmap function calls. I am not completly sure what
> > you mean by an iommu_context. Can you describe what it means in your
> > context?
> 
> Joerg,
> I think with some rework, all my use cases can be handled by your 
> existing iommu API. If the domain is treated basically a page table, 
> there will be some changes, but I think it can be done. I will push a 
> new version of my driver in a few days.
> 
> One thing that may be helpful for the future, however, is maybe 
> something like adding iommu_tlb_flush to the ops. I suppose this would 
> either have to take a device, or the domain would need to keep a list of 
> devices it had been attached to (so that their TLBs can be invalidated). 
> But I suppose on the other hand, iommu_map/unmap may be able to just 
> implicitly invalidate the TLB also, since TLB invalidation often follows 
> map/unmap. What are your thoughts?

Sounds good. I am curious for your patches :-)

For the TLB-flush question, I think it would make sense to add iommu
tlb flushing functions to the IOMMU-API. We currently flush the TLB
implicitly in the map/unmap calls but thats very inefficient. It would
be better to have a seperate function for it in the API. The right
parameter for such a function is a domain. The IOMMU driver knows which
devices are attached to a domain an could easily flush all TLBs.

One alternative I can think of: An iommu_domain_commit() function which
syncs software changes of a domain to the hardware. The map/unmap calls
have to save which parts of the tlb need to be flushed and commit does
flush those parts then (or flush everything).

	Joerg

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