linux-kernel - Re: [EXT] Re: [PATCH] bus: fsl-mc: Add ACPI support for fsl-mc

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Date:   Fri, 31 Jan 2020 16:09:29 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Will Deacon <will@...nel.org>
Cc:     Robin Murphy <robin.murphy@....com>,
        Jon Nettleton <jon@...id-run.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Marc Zyngier <maz@...nel.org>,
        Makarand Pawagi <makarand.pawagi@....com>,
        Calvin Johnson <calvin.johnson@....com>, stuyoder@...il.com,
        nleeder@...eaurora.org, Ioana Ciornei <ioana.ciornei@....com>,
        Cristi Sovaiala <cristian.sovaiala@....com>,
        Hanjun Guo <guohanjun@...wei.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Pankaj Bansal <pankaj.bansal@....com>,
        Russell King <linux@...linux.org.uk>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Len Brown <lenb@...nel.org>,
        Jason Cooper <jason@...edaemon.net>,
        Andy Wang <Andy.Wang@....com>, Varun Sethi <V.Sethi@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Laurentiu Tudor <laurentiu.tudor@....com>,
        Paul Yang <Paul.Yang@....com>,
        "<netdev@...r.kernel.org>" <netdev@...r.kernel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Shameerali Kolothum Thodi 
        <shameerali.kolothum.thodi@...wei.com>,
        Sudeep Holla <sudeep.holla@....com>
Subject: Re: [EXT] Re: [PATCH] bus: fsl-mc: Add ACPI support for fsl-mc

> Devicetree to the rescue!

Yes, exactly. We have good, standardised descriptions for most of this
in device tree. And phylink can handle SFP and SFP+. Nobody has worked
on QSFP yet, since phylink has mostly been pushed by the embedded
world and 40G is not yet popular in the embedded world.

> Entertaining the use of ACPI without any firmware abstraction for this
> hardware really feels like a square peg / round hole situation, so I'm
> assuming somebody's telling you that you need it "FOAR ENTAPRYZE". Who
> is it and can you tell them to bog off?

The issues here is that SFPs are appearing in more and more server
systems, replacing plain old copper Ethernet. If the boxes use off the
shelf Mellanox or Intel PCIe cards, it is not an issue. But silicon
vendors are integrating this into the SoC in the ARM way of doing
things, memory mapped, spread over a number of controllers, not a
single PCIe device.

Maybe we need hybrid systems. Plain, old, simple, boring things like
CPUs, serial ports, SATA, PCIe busses are described in ACPI. Complex
interesting things are in DT. The hard thing is the interface between
the two. DT having a phandle to an ACPI object, e.g a GPIO, interrupt
or an i2c bus.

   Andrew