linux-kernel - Re: [PATCH v3 2/2] iommu/amd: Add basic debugfs infrastructure for AMD IOMMU

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Message-ID: <1524036520.2747.31.camel@intel.com>
Date:   Wed, 18 Apr 2018 07:27:28 +0000
From:   "Mehta, Sohil" <sohil.mehta@...el.com>
To:     "shunyong.yang@...-semitech.com" <shunyong.yang@...-semitech.com>,
        "gary.hook@....com" <gary.hook@....com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "ghook@....com" <ghook@....com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 2/2] iommu/amd: Add basic debugfs infrastructure for
 AMD IOMMU

On Wed, 2018-04-18 at 05:58 +0000, Yang, Shunyong wrote:
> Hi, Gary and Sohil,
> 
> On Tue, 2018-04-17 at 13:38 -0400, Hook, Gary wrote:
> > On 4/13/2018 8:08 PM, Mehta, Sohil wrote:
> > > 
> > > On Fri, 2018-04-06 at 08:17 -0500, Gary R Hook wrote:
> > > > 
> > > >   
> > > > +
> > > > +void amd_iommu_debugfs_setup(struct amd_iommu *iommu)
> > > > +{
> > > > + char name[MAX_NAME_LEN + 1];
> > > > + struct dentry *d_top;
> > > > +
> > > > + if (!debugfs_initialized())
> > > Probably not needed.
> > Right.
> 
> When will this check is needed?
> IMO, this function is to check debugfs ready status before we want to
> use debugfs. I just want to understand when we should use
> debugfs_initialized();
> 

You are right debugfs_initialized() can be used to check if debugfs is
ready. However in this case we can also rely on debugfs_create_dir()
which is called in iommu_debufs_setup().

debugfs_create_dir() says:

 * If debugfs is not enabled in the kernel, the value -%ENODEV will be
 * returned.

Sohil

> Thanks.
> Shunyong.
> 
> > 
> > > 
> > > 
> > > > 
> > > > +         return;
> > > > +
> > > > + mutex_lock(&amd_iommu_debugfs_lock);
> > > > + if (!amd_iommu_debugfs) {
> > > > +         d_top = iommu_debugfs_setup();
> > > > +         if (d_top)
> > > > +                 amd_iommu_debugfs =
> > > > debugfs_create_dir("amd", d_top);
> > > > + }
> > > > + mutex_unlock(&amd_iommu_debugfs_lock);