linux-kernel - Re: [PATCH v4 2/3] iommu/tegra-smmu: Rework tegra_smmu_probe

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Message-ID: <ae48aaaf-fe10-6de4-06bb-2afbde799168@gmail.com>
Date:   Mon, 5 Oct 2020 13:36:55 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Thierry Reding <thierry.reding@...il.com>
Cc:     Nicolin Chen <nicoleotsuka@...il.com>, joro@...tes.org,
        vdumpa@...dia.com, jonathanh@...dia.com,
        linux-tegra@...r.kernel.org, iommu@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 2/3] iommu/tegra-smmu: Rework tegra_smmu_probe_device()

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.