linux-kernel - Re: your mail

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Message-ID: <20140224172850.GG2553@mudshark.cambridge.arm.com>
Date:	Mon, 24 Feb 2014 17:28:50 +0000
From:	Will Deacon <will.deacon@....com>
To:	srikanth TS <srikantht.shivanand@...il.com>
Cc:	"iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"ts.srikanth@...sung.com" <ts.srikanth@...sung.com>,
	"sungjinn.chung@...sung.com" <sungjinn.chung@...sung.com>
Subject: Re: your mail

On Mon, Feb 24, 2014 at 03:12:21PM +0000, srikanth TS wrote:
> Hi Will Deacon,

Hello,

> Currently SMMU driver expecting all stream ID used by respective master
> should be defined in the DT.
> 
> We want to know how to handle in the case of virtual functions dynamically
> created and destroyed.
> 
> Is PCI driver responsible for creating stream ID respective BDand
> requesting SMMU to add to the mapping table[stream Id to context mapping
> table]?
> 
> Or is there any right way of doing it?

Correct, the driver currently doesn't support dynamic mappings (mainly
because I didn't want to try and invent something that I couldn't test).

There are a couple of ways to solve this:

  (1) Add a way for a PCI RC to dynamically allocate StreamIDs on an SMMU
      within a fixed range. That would probably need some code in the bus
      layer, so that a bus notifier can kick and call back to the relevant
      SMMU.

  (2) Describe the RID -> SID mapping in the device-tree. We probably want
      to avoid an enormous table, so this would only work for simple `SID =
      RID + offset' or 'SID = RID & mask' cases.

How do your IDs map to each other?

Will
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