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

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Date:   Wed, 20 Apr 2022 09:48:58 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     Tony Luck <tony.luck@...el.com>,
        Hans de Goede <hdegoede@...hat.com>, 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, patches@...ts.linux.dev,
        Ravi V Shankar <ravi.v.shankar@...el.com>
Subject: Re: [PATCH v3 03/11] platform/x86/intel/ifs: Create device for Intel
 IFS (In Field Scan)

On Tue, Apr 19, 2022 at 11:09:09AM -0700, Dan Williams wrote:
> On Tue, Apr 19, 2022 at 9:48 AM Greg KH <gregkh@...uxfoundation.org> wrote:
> >
> > On Tue, Apr 19, 2022 at 09:38:51AM -0700, Tony Luck wrote:
> > > The initial implementation of IFS is model specific. Enumeration is
> > > via a combination of family-model-stepping and a check for a bit in the
> > > CORE_CAPABILITIES MSR.
> > >
> > > Linux has handled this lack of enumeration before with a code stub to
> > > create a device.  See arch/x86/kernel/pmem.c. Use the same approach
> > > here.
> >
> > Ick, why?  Why not just create a simple virtual device and use that?  Do
> > you really want to bind a driver to this?  Or do you already "know" the
> > only driver that you have will bind to this?
> 
> With the realization that there may be multiple instances of an
> IFS-like capability going forward, and that ideally those capabilities
> would move away from a CPU capability bit to an ACPI description, then
> it seemed to me that a simulated platform_device for this is a
> reasonable fit. I.e. when / if an ACPI _HID is assigned for this
> capability the same platform_driver can be reused for those instances.

Don't write code today for stuff you do not have right now, you all know
that.  We can always revisit it in the future.

thanks,

greg k-h