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

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Message-ID: <6a98ba41-34ee-4493-b0ea-0c24d7e979b1@lunn.ch>
Date: Thu, 13 Mar 2025 21:40:27 +0100
From: Andrew Lunn <andrew@...n.ch>
To: Chris Packham <Chris.Packham@...iedtelesis.co.nz>
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

On Thu, Mar 13, 2025 at 08:37:18PM +0000, Chris Packham wrote:
> On 14/03/2025 09:35, Andrew Lunn wrote:
> > On Thu, Mar 13, 2025 at 07:54:39PM +0000, Chris Packham wrote:
> >> +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.
> > Is there more to it than this? Because why not just set the mode per
> > bus transaction?
> 
> It's a bus level setting at init time. You can't dynamically switch modes.

Why not? The bus is only every doing one transaction at a time, so why
not switch it per transaction?

	Andrew