RE: [PATCH v2 1/3] platform/x86: Add Intel Input Output Manager (IOM) driver

[Mani, Rajmohan]

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

> 
> thanks,
> 
> --
> heikki