From: Will Deacon <will@kernel.org>
To: Bjorn Andersson <bjorn.andersson@linaro.org>
Cc: linux-arm-msm <linux-arm-msm@vger.kernel.org>,
iommu@lists.linux-foundation.org,
Thierry Reding <thierry.reding@gmail.com>,
John Stultz <john.stultz@linaro.org>,
linux-tegra@vger.kernel.org, Robin Murphy <robin.murphy@arm.com>,
linux-arm-kernel <linux-arm-kernel@lists.infradead.org>
Subject: Re: [RFC 0/2] iommu: arm-smmu: Add support for early direct mappings
Date: Wed, 1 Jul 2020 11:54:54 +0100 [thread overview]
Message-ID: <20200701105453.GG14959@willie-the-truck> (raw)
In-Reply-To: <20200701074050.GO388985@builder.lan>
On Wed, Jul 01, 2020 at 12:40:50AM -0700, Bjorn Andersson wrote:
> On Wed 03 Jun 04:00 PDT 2020, Robin Murphy wrote:
> > at that point I'm inclined to suggest we give up and stop trying to
> > drive these things with arm-smmu. The XZR thing was bad enough, but if
> > they're not even going to pretend to implement the architecture correctly
> > then I'm not massively keen to continue tying the architectural driver in
> > further knots if innocent things like CONFIG_IOMMU_DEFAULT_PASSTHROUGH are
> > going to unexpectedly and catastrophically fail. We have qcom-iommu for
> > hypervisor-mediated SMMUs, and this new hypervisor behaviour sounds to me
> > more like "qcom-iommu++" with reassignable stream-to-context mappings,
> > rather than a proper Arm SMMU emulation.
> >
>
> I've been going through over and over, hoping to perhaps be able to
> evolve qcom_iommu into a qcom-iommu++, but afaict the new hypervisor is
> different enough that this isn't feasible. In particular, the platforms
> using qcom_iommu relies entirely on the hypervisor to configure stream
> mapping etc - and we can't even read most of the registers.
>
> On the other hand I agree with you that we're messing around quite a bit
> with the arm-smmu driver, and I'm uncertain where we are on supporting
> the various GPU features, so I'm adding Jordan to the thread.
>
> So, afaict we have the options of either shoehorning this too into the
> arm-smmu driver or we essentially fork arm-smmu.c to create a
> qcom-smmu.c.
>
> While I don't fancy the code duplication, it would allow us to revert
> the Qualcomm quirks from arm-smmu and would unblock a number of
> activities that we have depending on getting the SMMU enabled on various
> platforms.
We added the impl hooks to cater for implementation differences, so I'd
still prefer to see this done as part of arm-smmu than introduce another
almost-the-same-but-not-quite IOMMU driver that has the lifetime of
a single SoC.
Will
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next prev parent reply other threads:[~2020-07-01 10:55 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-09 15:07 [RFC 0/2] iommu: arm-smmu: Add support for early direct mappings Thierry Reding
2019-12-09 15:07 ` [RFC 1/2] iommu: arm-smmu: Extract arm_smmu_of_parse() Thierry Reding
2019-12-09 15:07 ` [RFC 2/2] iommu: arm-smmu: Add support for early direct mappings Thierry Reding
2020-01-11 4:56 ` [RFC 0/2] " Saravana Kannan via iommu
2020-01-13 14:07 ` Thierry Reding
2020-01-13 22:01 ` Saravana Kannan via iommu
2020-01-14 0:11 ` Bjorn Andersson
2020-02-28 2:57 ` Bjorn Andersson
2020-03-04 13:48 ` Laurentiu Tudor
2020-05-14 19:32 ` bjorn.andersson
2020-05-26 20:34 ` John Stultz
2020-05-27 9:06 ` Laurentiu Tudor
2020-05-27 11:03 ` Will Deacon
2020-06-02 6:32 ` Bjorn Andersson
2020-06-03 11:00 ` Robin Murphy
2020-07-01 7:40 ` Bjorn Andersson
2020-07-01 10:54 ` Will Deacon [this message]
2020-06-03 11:11 ` Will Deacon
2020-06-03 17:23 ` Bjorn Andersson
2020-06-02 11:02 ` Thierry Reding
2020-06-02 19:32 ` Bjorn Andersson
2020-06-03 10:24 ` Thierry Reding
2020-06-03 17:17 ` Bjorn Andersson
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