netdev - Re: [net-next PATCH v7 1/6] Documentation: ACPI: DSD: Document MDIO PHY

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Message-ID: <20200724191436.GH1594328@lunn.ch>
Date:   Fri, 24 Jul 2020 21:14:36 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Jeremy Linton <jeremy.linton@....com>
Cc:     Calvin Johnson <calvin.johnson@....nxp.com>,
        Russell King - ARM Linux admin <linux@...linux.org.uk>,
        Jon <jon@...id-run.com>,
        Cristi Sovaiala <cristian.sovaiala@....com>,
        Ioana Ciornei <ioana.ciornei@....com>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Madalin Bucur <madalin.bucur@....nxp.com>,
        netdev@...r.kernel.org, linux.cj@...il.com,
        linux-acpi@...r.kernel.org
Subject: Re: [net-next PATCH v7 1/6] Documentation: ACPI: DSD: Document MDIO
 PHY

> Hence my previous comment that we should consider this an escape
> hatch rather than the last word in how to describe networking on
> ACPI/SBSA platforms.

One problem i have is that this patch set suggests ACPI can be used to
describe complex network hardware. It is opening the door for others
to follow and add more ACPI support in networking. How long before it
is not considered an escape hatch, but the front door?

For an example, see

https://patchwork.ozlabs.org/project/netdev/patch/1595417547-18957-3-git-send-email-vikas.singh@puresoftware.com/

It is hard to see what the big picture is here. The [0/2] patch is not
particularly good. But it makes it clear that people are wanting to
add fixed-link PHYs into ACPI. These are pseudo devices, used to make
the MAC think it is connected to a PHY when it is not. The MAC still
gets informed of link speed, etc via the standard PHYLIB API. They are
mostly used for when the Ethernet MAC is directly connected to an
Ethernet Switch, at a MAC to MAC level.

Now i could be wrong, but are Ethernet switches something you expect
to see on ACPI/SBSA platforms? Or is this a legitimate use of the
escape hatch?

       Andrew