linux-kernel - Re: [PATCH v3 2/6] iommu/vt-d: Add Intel IOMMU debugfs to show context internals

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Date:   Thu, 7 Dec 2017 20:19:42 +0000
From:   "Mehta, Sohil" <sohil.mehta@...el.com>
To:     "joro@...tes.org" <joro@...tes.org>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "baolu.lu@...ux.intel.com" <baolu.lu@...ux.intel.com>
CC:     "Yu, Fenghua" <fenghua.yu@...el.com>,
        "Shankar, Ravi V" <ravi.v.shankar@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Kammela, Gayatri" <gayatri.kammela@...el.com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "dwmw2@...radead.org" <dwmw2@...radead.org>,
        "Shevchenko, Andriy" <andriy.shevchenko@...el.com>
Subject: Re: [PATCH v3 2/6] iommu/vt-d: Add Intel IOMMU debugfs to show
 context internals

On Wed, 2017-12-06 at 16:16 +0800, Lu Baolu wrote:
> Hi,
> 
> On 12/06/2017 11:43 AM, Sohil Mehta wrote:
> > 
> > From: Gayatri Kammela <gayatri.kammela@...el.com>
> > 
> > 
> > +	seq_printf(m, "%s Context table entries for Bus: %d\n",
> > +		   ext ? "Lower" : "", bus);
> > +	seq_printf(m, "[entry]\tDID :B :D .F\tLow\t\tHigh\n");
> WARNING: Prefer seq_puts to seq_printf
> #119: FILE: drivers/iommu/intel-iommu-debug.c:59:
> +    seq_printf(m, "[entry]\tDID :B :D .F\tLow\t\tHigh\n");
> 
> (caught by checkpatch.pl)
> 

Hi Lu,

We'll fix this and the other checkpatch.pl warnings.


> > +
> > +static void root_tbl_entry_show(struct seq_file *m, void *unused,
> Why do you define the "unused" parameter which will never been used?
> The same questions to other show functions.
> 

Some functions in our code that are registered with seq_file needed to
have an unused parameter since seq_file.h defines the show function as:
	int (*show) (struct seq_file *m, void *v);

But a lot of other functions including the one you pointed don't need
to have the unused parameter. We'll remove it from those.


> > +void __init intel_iommu_debugfs_init(void)
> > +{
> > +	struct dentry *iommu_debug_root;
> > +
> > +	iommu_debug_root = debugfs_create_dir("intel_iommu",
> > NULL);
> > +
> > +	if (!iommu_debug_root) {
> > +		pr_err("can't create debugfs dir\n");
> I don't think we need a pr_err() here. System works well even
> debugfs_create_dir() returns NULL.
> 
> This is same to all pr_err() in this file.
> 

Would the recommendation be to use pr_warn instead of pr_err or should
we entirely skip the message altogether?

Thanks,
Sohil