From: Nicolin Chen <nicoleotsuka@gmail.com>
To: Thierry Reding <thierry.reding@gmail.com>
Cc: Dmitry Osipenko <digetx@gmail.com>,
joro@8bytes.org, vdumpa@nvidia.com, jonathanh@nvidia.com,
linux-tegra@vger.kernel.org, iommu@lists.linux-foundation.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v4 2/3] iommu/tegra-smmu: Rework tegra_smmu_probe_device()
Date: Mon, 5 Oct 2020 18:05:46 -0700 [thread overview]
Message-ID: <20201006010546.GB28640@Asurada-Nvidia> (raw)
In-Reply-To: <20201005095754.GJ425362@ulmo>
On Mon, Oct 05, 2020 at 11:57:54AM +0200, Thierry Reding wrote:
> On Fri, Oct 02, 2020 at 11:58:29AM -0700, Nicolin Chen wrote:
> > On Fri, Oct 02, 2020 at 06:02:18PM +0300, Dmitry Osipenko wrote:
> > > 02.10.2020 09:08, Nicolin Chen 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);
> > >
> > > of_find_device_by_node() takes device reference and not the np
> > > reference. This is a bug, please remove of_node_put().
> >
> > Looks like so. Replacing it with put_device(&iommu_pdev->dev);
>
> Putting the put_device() here is wrong, though. You need to make sure
> you keep a reference to it as long as you keep accessing the data that
> is owned by it.
I am confused. You said in the other reply (to Dmitry) that we do
need to put_device(mc->dev), where mc->dev should be the same as
iommu_pdev->dev. But here your comments sounds that we should not
put_device at all since ->probe_device/group_device/attach_dev()
will use it later.
> Like I said earlier, this is a bit weird in this case because we're
> self-referencing, so iommu_pdev->dev is going to stay around as long as
> the SMMU is. However, it might be worth to properly track the lifetime
> anyway just so that the code can serve as a good example of how to do
> things.
What's this "track-the-lifetime"?
> If you decide to go for the shortcut and not track this reference
> properly, then at least you need to add a comment as to why it is safe
> to do in this case. This ensures that readers are away of the
> circumstances and don't copy this bad code into a context where the
> circumstances are different.
I don't quite get this "shortcut" here either...mind elaborating?
next prev parent reply other threads:[~2020-10-06 1:12 UTC|newest]
Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-02 6:08 [PATCH v4 0/3] iommu/tegra-smmu: Add PCI support Nicolin Chen
2020-10-02 6:08 ` [PATCH v4 1/3] iommu/tegra-smmu: Use fwspec in tegra_smmu_(de)attach_dev Nicolin Chen
2020-10-02 14:22 ` Dmitry Osipenko
2020-10-02 14:52 ` Dmitry Osipenko
2020-10-02 19:56 ` Nicolin Chen
2020-10-02 14:26 ` Dmitry Osipenko
2020-10-02 14:41 ` Dmitry Osipenko
2020-10-02 19:45 ` Nicolin Chen
2020-10-02 20:12 ` Dmitry Osipenko
2020-10-02 23:53 ` Nicolin Chen
2020-10-03 4:01 ` Dmitry Osipenko
2020-10-02 6:08 ` [PATCH v4 2/3] iommu/tegra-smmu: Rework tegra_smmu_probe_device() Nicolin Chen
2020-10-02 14:22 ` Dmitry Osipenko
2020-10-02 14:58 ` Dmitry Osipenko
2020-10-02 19:53 ` Nicolin Chen
2020-10-05 9:47 ` Thierry Reding
2020-10-02 14:22 ` Dmitry Osipenko
2020-10-02 14:50 ` Dmitry Osipenko
2020-10-05 9:53 ` Thierry Reding
2020-10-05 10:36 ` Dmitry Osipenko
2020-10-05 11:15 ` Thierry Reding
2020-10-05 13:28 ` Dmitry Osipenko
2020-10-05 14:22 ` Thierry Reding
2020-10-05 9:51 ` Thierry Reding
2020-10-02 14:23 ` Dmitry Osipenko
2020-10-02 18:01 ` Nicolin Chen
2020-10-02 18:20 ` Dmitry Osipenko
2020-10-02 15:02 ` Dmitry Osipenko
2020-10-02 18:58 ` Nicolin Chen
2020-10-05 9:57 ` Thierry Reding
2020-10-06 1:05 ` Nicolin Chen [this message]
2020-10-08 9:53 ` Thierry Reding
2020-10-08 21:12 ` Nicolin Chen
2020-10-09 12:25 ` Thierry Reding
2020-10-09 15:54 ` Nicolin Chen
2020-10-02 15:23 ` Dmitry Osipenko
2020-10-02 16:00 ` Dmitry Osipenko
2020-10-02 16:37 ` Dmitry Osipenko
2020-10-02 16:50 ` Dmitry Osipenko
2020-10-02 6:08 ` [PATCH v4 3/3] iommu/tegra-smmu: Add PCI support Nicolin Chen
2020-10-02 14:35 ` Dmitry Osipenko
2020-10-02 17:45 ` Nicolin Chen
2020-10-02 18:04 ` Dmitry Osipenko
2020-10-02 18:04 ` Dmitry Osipenko
2020-10-05 10:04 ` Thierry Reding
2020-10-06 0:54 ` Nicolin Chen
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