linux-kernel - Re: [net-next PATCH 2/6] net: pcs: Implement OF support for PCS driver

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Message-ID: <Z9rgB1Ko_xAj44zS@shell.armlinux.org.uk>
Date: Wed, 19 Mar 2025 15:17:27 +0000
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Christian Marangi <ansuelsmth@...il.com>
Cc: Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Heiner Kallweit <hkallweit1@...il.com>,
	Philipp Zabel <p.zabel@...gutronix.de>,
	Daniel Golle <daniel@...rotopia.org>, netdev@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	upstream@...oha.com
Subject: Re: [net-next PATCH 2/6] net: pcs: Implement OF support for PCS
 driver

On Wed, Mar 19, 2025 at 12:58:38AM +0100, Christian Marangi wrote:
> Implement the foundation of OF support for PCS driver.
> 
> To support this, implement a simple Provider API where a PCS driver can
> expose multiple PCS with an xlate .get function.
> 
> PCS driver will have to call of_pcs_add_provider() and pass the device
> node pointer and a xlate function to return the correct PCS for the
> requested interface and the passed #pcs-cells.
> 
> This will register the PCS in a global list of providers so that
> consumer can access it.
> 
> Consumer will then use of_pcs_get() to get the actual PCS by passing the
> device_node pointer, the index for #pcs-cells and the requested
> interface.
> 
> For simple implementation where #pcs-cells is 0 and the PCS driver
> expose a single PCS, the xlate function of_pcs_simple_get() is
> provided. In such case the passed interface is ignored and is expected
> that the PCS supports any interface mode supported by the MAC.
> 
> For advanced implementation a custom xlate function is required. Such
> function should return an error if the PCS is not supported for the
> requested interface type.
> 
> This is needed for the correct function of of_phylink_mac_select_pcs()
> later described.
> 
> PCS driver on removal should first call phylink_pcs_release() on every
> PCS the driver provides and then correctly delete as a provider with
> the usage of of_pcs_del_provider().
> 
> A generic function for .mac_select_pcs is provided for any MAC driver
> that will declare PCS in DT, of_phylink_mac_select_pcs().
> This function will parse "pcs-handle" property and will try every PCS
> declared in DT until one that supports the requested interface type is
> found. This works by leveraging the return value of the xlate function
> returned by of_pcs_get() and checking if it's an ERROR or NULL, in such
> case the next PCS in the phandle array is tested.
> 
> Some additional helper are provided for xlate functions,
> pcs_supports_interface() as a simple function to check if the requested
> interface is supported by the PCS and phylink_pcs_release() to release a
> PCS from a phylink instance.
> 
> Co-developed-by: Daniel Golle <daniel@...rotopia.org>
> Signed-off-by: Daniel Golle <daniel@...rotopia.org>
> Signed-off-by: Christian Marangi <ansuelsmth@...il.com>

As a general comment, should we be developing stuff that is DT-centric
or fwnode-centric. We already have users of phylink using swnodes, and
it seems bad to design something today that is centred around just one
method of describing something.

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