netdev - Re: [RFC net-next PATCH 06/16] net: phylink: Add function for optionally adding a PCS

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Date:   Tue, 5 Oct 2021 12:17:38 -0400
From:   Sean Anderson <sean.anderson@...o.com>
To:     Andrew Lunn <andrew@...n.ch>,
        "Russell King (Oracle)" <linux@...linux.org.uk>
Cc:     netdev@...r.kernel.org, "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, linux-kernel@...r.kernel.org,
        Heiner Kallweit <hkallweit1@...il.com>
Subject: Re: [RFC net-next PATCH 06/16] net: phylink: Add function for
 optionally adding a PCS



On 10/5/21 9:43 AM, Andrew Lunn wrote:
> On Tue, Oct 05, 2021 at 10:51:38AM +0100, Russell King (Oracle) wrote:
>> On Mon, Oct 04, 2021 at 03:15:17PM -0400, Sean Anderson wrote:
>> > This adds a function to set the PCS only if there is not one currently
>> > set. The intention here is to allow MAC drivers to have a "default" PCS
>> > (such as an internal one) which may be used when one has not been set
>> > via the device tree. This allows for backwards compatibility for cases
>> > where a PCS was automatically attached if necessary.
>>
>> I'm not sure I entirely like this approach. Why can't the network
>> driver check for the pcs-handle property and avoid using its
>> "default" if present?
>
> And that would also be in line with
>
> ethernet/freescale/dpaa2/dpaa2-mac.c:	node = fwnode_find_reference(dpmac_node, "pcs-handle", 0);
>
> We need a uniform meaning of pcs-handle. And dpaa2-mac.c has set the
> precedent that the MAC uses it, not phylink. That can however be
> changed, if it make sense, but both users should do the same.

The tricky bit here happens when drivers set the PCS in mac_prepare()
depending on the interface. So you have to remember during probe()
whether you are supposed to set the PCS for later. I would like to leave
more of this to phylink to ensure that the process is done in a uniform
way.

--Sean