From: Rob Clark <robdclark@gmail.com>
To: Will Deacon <will.deacon@arm.com>
Cc: Arnd Bergmann <arnd@arndb.de>,
Thierry Reding <thierry.reding@gmail.com>,
Rob Herring <robh+dt@kernel.org>, Pawel Moll <Pawel.Moll@arm.com>,
Mark Rutland <Mark.Rutland@arm.com>,
Ian Campbell <ijc+devicetree@hellion.org.uk>,
Kumar Gala <galak@codeaurora.org>,
Stephen Warren <swarren@wwwdotorg.org>,
Joerg Roedel <joro@8bytes.org>,
Olav Haugan <ohaugan@codeaurora.org>,
"devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
Grant Grundler <grundler@chromium.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Marc Zyngier <Marc.Zyngier@arm.com>,
"iommu@lists.linux-foundation.org"
<iommu@lists.linux-foundation.org>,
"linux-tegra@vger.kernel.org" <linux-tegra@vger.kernel.org>,
Varun Sethi <varun.sethi@freescale.com>,
Cho KyongHo <pullip.cho@samsung.com>,
Dave P Martin <Dave.Martin@arm.com>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>,
Hiroshi Doyu <hdoyu@nvidia.com>,
linux-arm-msm <linux-arm-msm@vger.kernel.org>
Subject: Re: [PATCH v4] devicetree: Add generic IOMMU device tree bindings
Date: Sun, 13 Jul 2014 07:43:08 -0400 [thread overview]
Message-ID: <CAF6AEGt5cQhDCZgYX4=M1EKE=n2J=9G6mO02JMx-+Fcq_0ukfw@mail.gmail.com> (raw)
In-Reply-To: <20140713094341.GB23235@arm.com>
On Sun, Jul 13, 2014 at 5:43 AM, Will Deacon <will.deacon@arm.com> wrote:
> On Sat, Jul 12, 2014 at 01:57:31PM +0100, Rob Clark wrote:
>> On Sat, Jul 12, 2014 at 8:22 AM, Arnd Bergmann <arnd@arndb.de> wrote:
>> > On Saturday 12 July 2014, Rob Clark wrote:
>> >> >> Was there actually a good reason for having the device link to the
>> >> >> iommu rather than the other way around? How much would people hate it
>> >> >> if I just ignore the generic bindings and use something that works for
>> >> >> me instead. I mean, it isn't exactly like there is going to be .dts
>> >> >> re-use across different SoC's.. and at least with current IOMMU API
>> >> >> some sort of of_get_named_iommu() API doesn't really make sense.
>> >> >
>> >> > The thing is, if you end up ignoring the generic binding then we have two
>> >> > IOMMUs using the same (ARM SMMU) binding and it begs the question as to
>> >> > which is the more generic! I know we're keen to get this merged, but merging
>> >> > something that people won't use and calling it generic doesn't seem ideal
>> >> > either. We do, however, desperately need a generic binding.
>> >>
>> >> yeah, ignoring the generic binding is not my first choice. I'd rather
>> >> have something that works well for everyone. But I wasn't really sure
>> >> if the current proposal was arbitrary, or if there are some
>> >> conflicting requirements between different platforms.
>> >
>> > The common case that needs to be simple is attaching one (master) device
>> > to an IOMMU using the shared global context for the purposes of implementing
>> > the dma-mapping API.
>>
>> well, I don't disagree that IOMMU API has some problems. It is too
>> tied to the bus type, which doesn't really seem to make sense for
>> platform devices. (Unless we start having multiple platform busses?)
>>
>> But at least given the current IOMMU API I'm not really sure how it
>> makes a difference which way the link goes. But if there has already
>> been some discussion about how you want to handle the tie in with
>> dma-mapping, if you could point me at that then maybe your point will
>> make more sense to me.
>
> If you look at the proposed binding in isolation, I think it *is* cleaner
> than the ARM SMMU binding (I've acked it...) and I believe it's more
> consistent with the way we describe linkages elsewhere.
>
> However, the issue you're raising is that it's more difficult to make use of
> in a Linux IOMMU driver. The reward you'll get for using it will come
> eventually when the DMA ops are automatically swizzled for devices using the
> generic binding.
>
> My plan for the ARM SMMU driver is:
>
> (1) Change ->probe() to walk the device-tree looking for all masters with
> phandles back to the SMMU instance being probed
>
> (2) For each master, extract the Stream IDs and add them to the internal
> SMMU driver data structures (an rbtree per SMMU instance). For
> hotpluggable buses, we'll need a way for the bus controller to
> reserve a range of IDs -- this will likely be a later extension to
> the binding.
>
> (3) When we get an ->add() call, warn if it's a device we haven't seen
> and reject the addition.
>
> That way, ->attach() should be the same as it is now, I think.
>
> Have you tried implementing something like that? We agreed that (1) isn't
> pretty, but I don't have a good alternative and it's only done at
> probe-time.
I haven't tried implementing that yet, but I'm sure it would work. I
was just hoping to avoid having to do that ;-)
I suppose perhaps there is room for a shared helper here, to at least
avoid duplicating that in each IOMMU driver which needs the
stream-id's up front.
> Will
>
> BTW: Is the msm-v0 IOMMU compatible with the ARM SMMU driver, or is it a
> completely different design requiring a different driver?
My understanding is that it is different from msm v1 IOMMU, although I
think it shares the same pagetable format with v1. Not sure if that
is the same as arm-smmu? If so it might be nice to try to extract
out some shared helper fxns for map/unmap as well.
I expect Olav knows better the similarities/differences.
BR,
-R
next prev parent reply other threads:[~2014-07-13 11:43 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-07-04 15:29 [PATCH v4] devicetree: Add generic IOMMU device tree bindings Thierry Reding
2014-07-09 13:40 ` Will Deacon
2014-07-09 14:21 ` Thierry Reding
2014-07-09 18:10 ` Will Deacon
2014-07-10 9:49 ` Thierry Reding
2014-07-10 10:23 ` Will Deacon
2014-07-10 10:57 ` Thierry Reding
2014-07-10 12:38 ` Will Deacon
2014-07-11 20:55 ` Rob Clark
2014-07-12 9:39 ` Will Deacon
2014-07-12 11:26 ` Rob Clark
2014-07-12 12:22 ` Arnd Bergmann
2014-07-12 12:57 ` Rob Clark
2014-07-13 9:43 ` Will Deacon
2014-07-13 11:43 ` Rob Clark [this message]
2014-07-16 1:25 ` Olav Haugan
2014-07-16 10:10 ` Will Deacon
2014-07-16 20:24 ` Rob Clark
2014-07-14 6:44 ` Thierry Reding
2014-07-14 10:08 ` Will Deacon
2014-07-14 6:24 ` Thierry Reding
2014-07-14 10:13 ` Rob Clark
2014-07-14 6:15 ` Thierry Reding
2014-07-30 11:04 ` Will Deacon
2014-07-30 13:23 ` Thierry Reding
2014-07-30 13:33 ` Joerg Roedel
2014-07-30 17:37 ` Olof Johansson
2014-07-30 14:30 ` Will Deacon
2014-07-30 18:08 ` Rob Herring
2014-07-30 20:11 ` Arnd Bergmann
2014-07-30 15:26 ` Mark Rutland
2014-07-30 17:35 ` Olof Johansson
2014-07-30 18:18 ` Mark Rutland
2014-07-31 10:09 ` Thierry Reding
2014-07-31 10:50 ` Mark Rutland
2014-07-31 11:14 ` Thierry Reding
2014-07-31 9:51 ` Thierry Reding
2014-07-31 8:39 ` Thierry Reding
2014-07-31 9:22 ` Mark Rutland
2014-07-31 10:18 ` Thierry Reding
2014-07-31 10:23 ` Joerg Roedel
2014-07-31 10:46 ` Thierry Reding
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