linux-kernel - Re: [PATCH v5 2/3] iommu/tegra-smmu: Rework tegra_smmu_probe

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Date:   Sat, 3 Oct 2020 17:19:06 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Nicolin Chen <nicoleotsuka@...il.com>, thierry.reding@...il.com,
        joro@...tes.org
Cc:     vdumpa@...dia.com, jonathanh@...dia.com,
        linux-tegra@...r.kernel.org, iommu@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 2/3] iommu/tegra-smmu: Rework tegra_smmu_probe_device()

03.10.2020 09:59, Nicolin Chen пишет:
> The bus_set_iommu() in tegra_smmu_probe() enumerates all clients
> to call in tegra_smmu_probe_device() where each client searches
> its DT node for smmu pointer and swgroup ID, so as to configure
> an fwspec. But this requires a valid smmu pointer even before mc
> and smmu drivers are probed. So in tegra_smmu_probe() we added a
> line of code to fill mc->smmu, marking "a bit of a hack".
> 
> This works for most of clients in the DTB, however, doesn't work
> for a client that doesn't exist in DTB, a PCI device for example.
> 
> Actually, if we return ERR_PTR(-ENODEV) in ->probe_device() when
> it's called from bus_set_iommu(), iommu core will let everything
> carry on. Then when a client gets probed, of_iommu_configure() in
> iommu core will search DTB for swgroup ID and call ->of_xlate()
> to prepare an fwspec, similar to tegra_smmu_probe_device() and
> tegra_smmu_configure(). Then it'll call tegra_smmu_probe_device()
> again, and this time we shall return smmu->iommu pointer properly.
> 
> So we can get rid of tegra_smmu_find() and tegra_smmu_configure()
> along with DT polling code by letting the iommu core handle every
> thing, except a problem that we search iommus property in DTB not
> only for swgroup ID but also for mc node to get mc->smmu pointer
> to call dev_iommu_priv_set() and return the smmu->iommu pointer.
> So we'll need to find another way to get smmu pointer.
> 
> Referencing the implementation of sun50i-iommu driver, of_xlate()
> has client's dev pointer, mc node and swgroup ID. This means that
> we can call dev_iommu_priv_set() in of_xlate() instead, so we can
> simply get smmu pointer in ->probe_device().
> 
> This patch reworks tegra_smmu_probe_device() by:
> 1) Removing mc->smmu hack in tegra_smmu_probe() so as to return
>    ERR_PTR(-ENODEV) in tegra_smmu_probe_device() during stage of
>    tegra_smmu_probe/tegra_mc_probe().
> 2) Moving dev_iommu_priv_set() to of_xlate() so we can get smmu
>    pointer in tegra_smmu_probe_device() to replace DTB polling.
> 3) Removing tegra_smmu_configure() accordingly since iommu core
>    takes care of it.
> 
> This also fixes a problem that previously we added all clients to
> iommu groups before iommu core initializes its default domain:
>     ubuntu@...son:~$ dmesg | grep iommu
>     platform smmu_benchmark: Adding to iommu group 0
>     platform 1003000.pcie: Adding to iommu group 1
>     platform 50000000.host1x: Adding to iommu group 2
>     platform 57000000.gpu: Adding to iommu group 3
>     platform 7000c400.i2c: Adding to iommu group 4
>     platform 7000c500.i2c: Adding to iommu group 4
>     platform 7000c700.i2c: Adding to iommu group 4
>     platform 7000d000.i2c: Adding to iommu group 4
>     iommu: Default domain type: Translated
> 
> Though it works fine with IOMMU_DOMAIN_UNMANAGED, but will have
> warnings if switching to IOMMU_DOMAIN_DMA:
>     iommu: Failed to allocate default IOMMU domain of type 0 for
>            group (null) - Falling back to IOMMU_DOMAIN_DMA
>     iommu: Failed to allocate default IOMMU domain of type 0 for
>            group (null) - Falling back to IOMMU_DOMAIN_DMA
> 
> Now, bypassing the first probe_device() call from bus_set_iommu()
> fixes the sequence:
>     ubuntu@...son:~$ dmesg | grep iommu
>     iommu: Default domain type: Translated 
>     tegra-i2c 7000c400.i2c: Adding to iommu group 0
>     tegra-i2c 7000c500.i2c: Adding to iommu group 0
>     tegra-i2c 7000d000.i2c: Adding to iommu group 0
>     tegra-pcie 1003000.pcie: Adding to iommu group 1
>     ...
> 
> Note that dmesg log above is testing with IOMMU_DOMAIN_UNMANAGED.
> 
> Signed-off-by: Nicolin Chen <nicoleotsuka@...il.com>
> ---

Everything looks good to me, apart from the very minor pending question
about the NULL-checking. Thanks!

Reviewed-by: Dmitry Osipenko <digetx@...il.com>
Tested-by: Dmitry Osipenko <digetx@...il.com>