linux-kernel - Re: [PATCH v3 03/11] platform/x86/intel/ifs: Create device for Intel IFS (In Field Scan)

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Message-ID: <YmBLJf8JQkfSQGvA@kroah.com>
Date:   Wed, 20 Apr 2022 20:04:21 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     "Luck, Tony" <tony.luck@...el.com>
Cc:     "Williams, Dan J" <dan.j.williams@...el.com>,
        Hans de Goede <hdegoede@...hat.com>,
        "markgross@...nel.org" <markgross@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        X86 ML <x86@...nel.org>, "H. Peter Anvin" <hpa@...or.com>,
        Jonathan Corbet <corbet@....net>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        "Joseph, Jithu" <jithu.joseph@...el.com>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Doc Mailing List <linux-doc@...r.kernel.org>,
        "platform-driver-x86@...r.kernel.org" 
        <platform-driver-x86@...r.kernel.org>,
        "patches@...ts.linux.dev" <patches@...ts.linux.dev>,
        "Shankar, Ravi V" <ravi.v.shankar@...el.com>
Subject: Re: [PATCH v3 03/11] platform/x86/intel/ifs: Create device for Intel
 IFS (In Field Scan)

On Wed, Apr 20, 2022 at 05:57:04PM +0000, Luck, Tony wrote:
> >> 	ifs_class = class_create(THIS_MODULE, "intel_ifs");
> >
> > Why do you need a class?  Why not just use a misc device?  Saves you
> > loads of boilerplate code that is sometimes tricky to get correct.
> 
> It didn't feel like a "ton" of boiler plate. Just class_create()/class_destroy()
> for the class itself. And
> 
> 	class_for_each_device(ifs_class, NULL, NULL, ifs_device_unregister);
> 
> to clean up devices on exit (or error cleanup in init()).
> 
> 
> I thought I needed a class to make a directory for my per-test directories to live in:
> 
> $ ls -l /sys/devices/virtual/intel_ifs
> total 0
> drwxr-xr-x 3 root root 0 Apr 20 13:36 ifs0
> drwxr-xr-x 3 root root 0 Apr 20 13:36 ifs1
> 
> Can I do that with a misc device?
> 
> Or is it ok for them all to sit at the top level of /sys/devices/virtual?

How many do you have?

And why is a directory needed for just one tiny driver type?

thanks,

greg k-h