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    SubjectRe: [PATCH v4 2/3] iommu/tegra-smmu: Rework tegra_smmu_probe_device()
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    05.10.2020 14:15, Thierry Reding пишет:
    > On Mon, Oct 05, 2020 at 01:36:55PM +0300, Dmitry Osipenko wrote:
    >> 05.10.2020 12:53, Thierry Reding пишет:
    >>> On Fri, Oct 02, 2020 at 05:50:08PM +0300, Dmitry Osipenko wrote:
    >>>> 02.10.2020 17:22, Dmitry Osipenko пишет:
    >>>>>> static int tegra_smmu_of_xlate(struct device *dev,
    >>>>>> struct of_phandle_args *args)
    >>>>>> {
    >>>>>> + struct platform_device *iommu_pdev = of_find_device_by_node(args->np);
    >>>>>> + struct tegra_mc *mc = platform_get_drvdata(iommu_pdev);
    >>>>>> u32 id = args->args[0];
    >>>>>>
    >>>>>> + of_node_put(args->np);
    >>>>>> +
    >>>>>> + if (!mc || !mc->smmu)
    >>>>>> + return -EPROBE_DEFER;
    >>>>> platform_get_drvdata(NULL) will crash.
    >>>>>
    >>>>
    >>>> Actually, platform_get_drvdata(NULL) can't happen. I overlooked this.
    >>>
    >>> How so? It's technically possible for the iommus property to reference a
    >>> device tree node for which no platform device will ever be created, in
    >>> which case of_find_device_by_node() will return NULL. That's very
    >>> unlikely and perhaps worth just crashing on to make sure it gets fixed
    >>> immediately.
    >>
    >> The tegra_smmu_ops are registered from the SMMU driver itself and MC
    >> driver sets platform data before SMMU is initialized, hence device is
    >> guaranteed to exist and mc can't be NULL.
    >
    > Yes, but that assumes that args->np points to the memory controller's
    > device tree node. It's obviously a mistake to do this, but I don't think
    > anyone will prevent you from doing this:
    >
    > iommus = <&{/chosen} 0>;
    >
    > In that case, since no platform device is created for the /chosen node,
    > iommu_pdev will end up being NULL and platform_get_drvdata() will crash.

    But then Tegra SMMU isn't associated with the device's IOMMU path, and
    thus, tegra_smmu_of_xlate() won't be invoked for this device.

    > That said, I'm fine with not adding a check for that. If anyone really
    > does end up messing this up they deserve the crash.
    >
    > I'm still a bit undecided about the mc->smmu check because I haven't
    > convinced myself yet that it can't happen.

    For now I can't see any realistic situation where mc->smmu could be NULL.

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