linux-kernel - Re: [PATCH v2 1/3] platform/x86: Add Intel Input Output Manager (IOM) driver

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Message-ID: <20200829062719.GA80106@kroah.com>
Date:   Sat, 29 Aug 2020 08:27:19 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     "Mani, Rajmohan" <rajmohan.mani@...el.com>
Cc:     Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Darren Hart <dvhart@...radead.org>,
        Andy Shevchenko <andy@...radead.org>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Lee Jones <lee.jones@...aro.org>,
        Ayman Bagabas <ayman.bagabas@...il.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        "Joseph, Jithu" <jithu.joseph@...el.com>,
        Blaž Hrastnik <blaz@...n.io>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "platform-driver-x86@...r.kernel.org" 
        <platform-driver-x86@...r.kernel.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "pmalani@...omium.org" <pmalani@...omium.org>,
        "bleung@...omium.org" <bleung@...omium.org>
Subject: Re: [PATCH v2 1/3] platform/x86: Add Intel Input Output Manager
 (IOM) driver

On Fri, Aug 28, 2020 at 03:20:22PM +0000, Mani, Rajmohan wrote:
> Hi Greg,
> 
> > Subject: Re: [PATCH v2 1/3] platform/x86: Add Intel Input Output Manager
> > (IOM) driver
> > 
> > Hi Greg,
> > 
> > On Fri, Aug 28, 2020 at 09:43:59AM +0200, Greg Kroah-Hartman wrote:
> > > I still find this crazy that a whole separate driver is created just
> > > to read a single 32bit value.
> > >
> > > Why not put this logic in the driver that wants to read that value?
> > > That would be much simpler, smaller, and more obvious.
> > 
> > That would mean that we start maintaining something like DMI quirk table in
> > those drivers. Unfortunately the IOM device is not available on every platform.
> > Also, even on platforms that do have it, there is no guarantee that the device is
> > always going to be mapped to the same address.
> > 
> > Nevertheless, I was originally hoping that we could hide the handling of IOM
> > somehow in ACPI without the need for an actual device object, but it now
> > turns out that the other features of the IOM chip have created interest. At
> > least our i915 guys probable have some use for it (I don't know exactly what
> > they are planning to use it for).
> > 
> > So the fact that we may later need the device for something else, on top of the
> > clumsiness and most importantly risks involved with using ACPI to take care of
> > extra tasks (ASL tends to have bugs - bugs that may never ever get fixed), I
> > think the IOM device object, and the driver that binds to it, do have a valid
> > reason for existing.
> > 
> 
> Intel PMC USB mux device is part of the PCH, while IOM is part of the SoC.

I have no idea what a "PCH" is, what "IOM" is, and how any of this
relates to a "SoC" :)

Don't impose arbritrary hardware "splits" to kernel code when the kernel
has no such "partitioning" please.

> This was another reason we had to have a separate ACPI device.

That sounds like a firmware issue you can solve in UEFI.

I think this is the most TLA-laden email I have ever written, and I used
to work at IBM :)

greg k-h