netdev - Re: [PATCH v3 2/8] net: dsa: Add DSA driver for Hirschmann Hellcreek switches

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Date:   Tue, 25 Aug 2020 16:48:19 +0200
From:   Kurt Kanzenbach <kurt@...utronix.de>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Richard Cochran <richardcochran@...il.com>,
        Kamil Alkhouri <kamil.alkhouri@...offenburg.de>,
        ilias.apalodimas@...aro.org, Vladimir Oltean <olteanv@...il.com>
Subject: Re: [PATCH v3 2/8] net: dsa: Add DSA driver for Hirschmann Hellcreek switches

On Tue Aug 25 2020, Andrew Lunn wrote:
> I agree with the check here. The question is about the compatible
> string. Should there be a more specific compatible string as well as
> the generic one?
>
> There have been a few discussions about how the Marvell DSA driver
> does its compatible string. The compatible string tells you where to
> find the ID register, not what value to expect in the ID register. The
> ID register can currently be in one of three different locations. Do
> all current and future Hellcreak devices have the same value for
> HR_MODID_C?  If not, now is a good time to add a more specific
> compatible string to tell you where to find the ID register.
>
>> My plan was to extend this when I have access to other
>> revisions. There will be a SPI variant as well. But, I didn't want to
>> implement it without the ability to test it.
>
> Does the SPI variant use the same value for HR_MODID_C?  Maybe you
> need a different compatible, maybe not, depending on how the driver is
> structured.
>
> The compatible string is part of the ABI. So thinking about it a bit
> now can make things easier later. I just want to make sure you have
> thought about this.

I totally agree. The Marvell solution seems to work. For all current
devices the module ID is located at 0x00. Depending on the chip ID the
different properties can be configured later. The SPI variant will have
a different module ID. Anyhow, I'll ask how this will be handled for
future devices and in general.

Thanks,
Kurt

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