linux-kernel - Re: [PATCH v8 6/6] iommu/tegra-smmu: Add pagetable mappings to debugfs

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Date:   Thu, 9 Dec 2021 11:32:54 -0800
From:   Nicolin Chen <nicolinc@...dia.com>
To:     Dmitry Osipenko <digetx@...il.com>
CC:     <thierry.reding@...il.com>, <joro@...tes.org>, <will@...nel.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 v8 6/6] iommu/tegra-smmu: Add pagetable mappings to
 debugfs

On Thu, Dec 09, 2021 at 05:47:18PM +0300, Dmitry Osipenko wrote:
> External email: Use caution opening links or attachments
> 
> 
> 09.12.2021 10:38, Nicolin Chen пишет:
> > @@ -545,6 +719,15 @@ static void tegra_smmu_detach_as(struct tegra_smmu *smmu,
> >               if (group->swgrp != swgrp)
> >                       continue;
> >               group->as = NULL;
> > +
> > +             if (smmu->debugfs_mappings) {
> 
> Do we really need this check?
> 
> Looks like all debugfs_create_dir() usages in this driver are incorrect,
> that function never returns NULL. Please fix this.

debugfs_create_dir returns ERR_PTR on failure. So here should be
to check !IS_ERR. Thanks for pointing it out!

> > +                     struct dentry *d;
> 
> The file name is wrong here.
> 
>                         if (group->soc)
>                                 name = group->soc->name;
>                         else
>                                 name = group->swgrp->name;

Yea, I'll add this.

> 
> > +                     d = debugfs_lookup(group->swgrp->name,
> > +                                        smmu->debugfs_mappings);
> > +                     debugfs_remove(d);
> > +             }
> 
> This now looks problematic to me. You created debugfs file when the
> first member of the shared group was attached to AS, now you remove this
> file when any device is detached. The shared debugfs file should be
> refcounted or something.a

Will see how to handle it.

Thanks
Nic