Re: [PATCH devicetree 2/2] MIPS: mscc: ocelot: mark the phy-mode for internal PHY ports

[Alexandre Belloni]

On 19/08/2021 17:17:05+0000, Vladimir Oltean wrote:
> On Thu, Aug 19, 2021 at 08:04:16PM +0300, Vladimir Oltean wrote:
> > The ocelot driver was converted to phylink, and that expects a valid
> > phy_interface_t. Without a phy-mode, of_get_phy_mode returns
> > PHY_INTERFACE_MODE_NA, which is not ideal because phylink rejects that.
> > 
> > The ocelot driver was patched to treat PHY_INTERFACE_MODE_NA as
> > PHY_INTERFACE_MODE_INTERNAL to work with the broken DT blobs, but we
> > should fix the device trees and specify the phy-mode too.
> > 
> > Signed-off-by: Vladimir Oltean <vladimir.oltean@xxxxxxx>
> > ---
> 
> Please note that the pre-phylink driver has this check:
> 
> 		switch (ocelot_port->phy_mode) {
> 		case PHY_INTERFACE_MODE_NA:
> 			(...)
> 		case PHY_INTERFACE_MODE_SGMII:
> 			(...)
> 		case PHY_INTERFACE_MODE_QSGMII:
> 			(...)
> 		default:
> 			dev_err(ocelot->dev,
> 				"invalid phy mode for port%d, (Q)SGMII only\n",
> 				port);
> 			of_node_put(portnp);
> 			err = -EINVAL;
> 			goto out_teardown;
> 		}
> 
> So it does not actually expect PHY_INTERFACE_MODE_INTERNAL and will
> error out.
> 
> Are we okay with the new device tree blobs breaking the old kernel?

>From my point of view, newer device trees are not required to work on
older kernel, this would impose an unreasonable limitation and the use
case is very limited.

-- 
Alexandre Belloni, co-owner and COO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com