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From:   Dan Williams <dan.j.williams@intel.com>
Date:   Tue, 19 Apr 2022 15:28:26 -0700
Message-ID: <CAPcyv4hBGgN=LqY55nf2K4E1OD0n=_axri4CNSKVneStYEp6rw@mail.gmail.com>
Subject: Re: [PATCH v3 03/11] platform/x86/intel/ifs: Create device for Intel
 IFS (In Field Scan)
To:     Greg KH <gregkh@linuxfoundation.org>
Cc:     Tony Luck <tony.luck@intel.com>,
        Hans de Goede <hdegoede@redhat.com>, markgross@kernel.org,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        X86 ML <x86@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        "Joseph, Jithu" <jithu.joseph@intel.com>,
        "Raj, Ashok" <ashok.raj@intel.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux Doc Mailing List <linux-doc@vger.kernel.org>,
        platform-driver-x86@vger.kernel.org, patches@lists.linux.dev,
        Ravi V Shankar <ravi.v.shankar@intel.com>
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On Tue, Apr 19, 2022 at 11:09 AM Dan Williams <dan.j.williams@intel.com> wrote:
>
> On Tue, Apr 19, 2022 at 9:48 AM Greg KH <gregkh@linuxfoundation.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.

Turns out the ACPI enumeration for this may not materialize, so this
can indeed move to a simple / driver-less device.