linux-kernel - Re: [PATCH v10] net: mdio: Add RTL9300 MDIO driver

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Message-ID: <5ea333ec-c2e4-4715-8a44-0fd2c77a4f3c@alliedtelesis.co.nz>
Date: Thu, 13 Mar 2025 19:54:39 +0000
From: Chris Packham <Chris.Packham@...iedtelesis.co.nz>
To: Andrew Lunn <andrew@...n.ch>
CC: "hkallweit1@...il.com" <hkallweit1@...il.com>, "linux@...linux.org.uk"
	<linux@...linux.org.uk>, "davem@...emloft.net" <davem@...emloft.net>,
	"edumazet@...gle.com" <edumazet@...gle.com>, "kuba@...nel.org"
	<kuba@...nel.org>, "pabeni@...hat.com" <pabeni@...hat.com>,
	"daniel@...rotopia.org" <daniel@...rotopia.org>, "markus.stockhausen@....de"
	<markus.stockhausen@....de>, "sander@...nheule.net" <sander@...nheule.net>,
	netdev <netdev@...r.kernel.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v10] net: mdio: Add RTL9300 MDIO driver

+cc netdev, lkml

On 14/03/2025 01:34, Andrew Lunn wrote:
>> +	/* Put the interfaces into C45 mode if required */
>> +	glb_ctrl_mask = GENMASK(19, 16);
>> +	for (i = 0; i < MAX_SMI_BUSSES; i++)
>> +		if (priv->smi_bus_is_c45[i])
>> +			glb_ctrl_val |= GLB_CTRL_INTF_SEL(i);
>> +
>> +	fwnode_for_each_child_node(node, child)
>> +		if (fwnode_device_is_compatible(child, "ethernet-phy-ieee802.3-c45"))
>> +			priv->smi_bus_is_c45[mdio_bus] = true;
>> +
> This needs more explanation. Some PHYs mix C22 and C45, e.g. the > 1G
> speed support registers are in the C45 address space, but <= 1G is in
> the C22 space. And 1G PHYs which support EEE need access to C45 space
> for the EEE registers.

Ah good point. The MDIO interfaces are either in GPHY (i.e. clause 22) 
or 10GPHY mode (i.e. clause 45). This does mean we can't support support 
both c45 and c22 on the same MDIO bus (whether that's one PHY that 
supports both or two different PHYs). I'll add a comment to that effect 
and I should probably only provide bus->read/write or 
bus->read_c45/write_c45 depending on the mode.