From: swarren@wwwdotorg•org (Stephen Warren)
To: linux-arm-kernel@lists•infradead.org
Subject: Report from 2013 ARM kernel summit
Date: Thu, 21 Nov 2013 11:40:28 -0700 [thread overview]
Message-ID: <528E539C.8080603@wwwdotorg.org> (raw)
In-Reply-To: <20131121110024.GA8395@mudshark.cambridge.arm.com>
On 11/21/2013 04:00 AM, Will Deacon wrote:
> On Wed, Nov 20, 2013 at 08:02:10PM +0000, Rob Herring wrote:
>> On Wed, Nov 20, 2013 at 12:39 AM, Hiroshi Doyu <hdoyu@nvidia•com> wrote:
>>> smmu_a: iommu at xxxxxxxx {
>>> #iommu-cells = <2>;
>>> ....
>>> };
>>>
>>> smmu_b: iommu at xxxxxxxx {
>>> #iommu-cells = <3>;
>>> ....
>>> };
>>>
>>> device_a {
>>> iommus = <&smmu_a param1 param2>,
>>> <&smmu_b param1 param2 param3>;
>>> };
>>>
>>> This can describe the relation between a device and an iommu
>>> independently. The number of params needed for each IOMMU can be
>>> sepcified by #iommu-cells in its iommu entry.
>>>
>>> device_a <-> smmu_a, needs 2 params for a device
>>> device_a <-> smmu_b, needs 3 params for a device
>>>
>>> For example, "smmu_a" can be an bus level global IOMMU where all child
>>> devices can be an master of "smmu_a", and "smmu_b" is a local IOMMU
>>> only for "device_a".
>>>
>>> "memory controller"---"smmu_a"---bus--+--"smmu_b"--"device_a"
>>> |
>>> |
>>> +--"device_b"
>>
>> I think the above binding would be the correct way to describe things
>> if you have 1 device connected to 2 IOMMUs (directly rather than
>> chained). IIUC, that is something you have on tegra?
>>
>> For the topology above where you are chaining iommu's, I think
>> something like this is more accurately describing the hierarchy:
>>
>> smmu_b: iommu at xxxxxxxx {
>> #iommu-cells = <3>;
>> iommus = <&smmu_a param1 param2>;
>> ....
>> };
>> device_a {
>> iommus = <&smmu_b param1 param2 param3>;
>> };
>>
>> I remember discussing this with Will and seem to recall some issue
>> with describing things this way. But looking at it now, I don't see
>> what that was.
>
> I think it was the usual issue with StreamID remastering. For example, if
^^^ s/was/had/ I assume
> you had a device going into two chained IOMMUs, you need a way to relate the
> StreamIDs of the device to the remastered IDs coming out of the first SMMU.
That seems pretty easy to deal with. Am I missing something. Here's how
I assume that would work:
1)
If the mapping is static in HW, then you simply have a table that
describes the remapping. A table representation could be in the DT or
the driver itself. Either way, any static mapping is a property of the
HW itself, so shouldn't need to leak into the client DT nodes at all, right?
That might look like:
smmu_a: iommu at xxxxxxxx {
#iommu-cells = <1>;
};
smmu_b: iommu at xxxxxxxx {
#iommu-cells = <1>;
// a) All stream IDs squashed down to 1 ID
iommus = <&smmu_a SMMU_B's_STREAM_ID_IN_SMMU_A>;
// OR b) stream IDs translated:
iommus = <&smmu_a 0>,
<&smmu_a 1>,
<&smmu_a 2> ...;
// this table could be in the driver instead
iommu-stream-id-map =
<DEV_A's_STREAM_ID_IN_SMMU_B 0>,
<DEV_B's_STREAM_ID_IN_SMMU_B 1>,
<DEV_C's_STREAM_ID_IN_SMMU_B 2>,
};
device_a {
iommus = <&smmu_b DEV_A's_STREAM_ID_IN_SMMU_B>;
};
or 2)
If the remapping is entirely dynamic, then you'd either need a table in
the DT to describe how to set it up for the particular use-case (similar
to the above), or a function in the driver to manage the mapping at
run-time, probably hooked into the of_xlate() of the parent IOMMU, which
would call into some function of the source IOMMU.
In other words, of_xlate for smmu_a would do both:
a) Parse the SMMU specifier in the client's iommus property
b) If the parse specifier represents a "dynamic stream ID device/IOMMU",
call some function in the client driver to find out which stream ID(s)
the parse iommus entry (specifier) represents.
next prev parent reply other threads:[~2013-11-21 18:40 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-11-08 13:20 Report from 2013 ARM kernel summit Grant Likely
2013-11-11 9:47 ` Hiroshi Doyu
2013-11-15 7:06 ` Grant Likely
2013-11-19 9:40 ` Hiroshi Doyu
2013-11-19 17:35 ` Will Deacon
2013-11-19 20:45 ` Rob Herring
2013-11-20 6:39 ` Hiroshi Doyu
2013-11-20 20:02 ` Rob Herring
2013-11-20 20:22 ` Stephen Warren
2013-11-21 8:49 ` Hiroshi Doyu
2013-11-21 11:00 ` Will Deacon
2013-11-21 18:40 ` Stephen Warren [this message]
2013-11-25 18:03 ` Will Deacon
2013-11-20 10:31 ` Will Deacon
2013-11-20 13:53 ` Thierry Reding
2013-11-20 19:47 ` Rob Herring
2013-11-20 20:22 ` Rob Herring
-- strict thread matches above, loose matches on Subject: below --
2013-11-07 23:29 Grant Likely
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