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

Open Source and information security mailing list archives

Date:   Wed, 18 Apr 2018 05:58:48 +0000
From:   "Yang, Shunyong" <shunyong.yang@...-semitech.com>
To:     "sohil.mehta@...el.com" <sohil.mehta@...el.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

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();

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);
> > 
> > You can do the above only once if you iterate over the IOMMUs here
> >   instead of doing it in amd_iommu_init.
> I'm not sure it matters, given the finite number of IOMMUs in a
> system, 
> and the fact that this work is done exactly once. However, removal of
> a 
> lock is fine thing, so I'll move this around.
> 
> > 
> > 
> > > 
> > > +	if (amd_iommu_debugfs) {
> > > +		snprintf(name, MAX_NAME_LEN, "iommu%02d", iommu-
> > > > 
> > > > index);
> > > +		iommu->debugfs = debugfs_create_dir(name,
> > > +						    amd_iommu_de
> > > bugf
> > > s);
> > > +		if (!iommu->debugfs) {
> > > +			debugfs_remove_recursive(amd_iommu_debug
> > > fs);
> > > +			amd_iommu_debugfs = NULL;
> > > +		}
> > > +	}
> > > +}
> > -Sohil
> > 
> _______________________________________________
> iommu mailing list
> iommu@...ts.linux-foundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/iommu

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