netdev - Re: [PATCH v2 net-next 2/2] net: mvpp2: support multiple comphy lanes

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Date:   Mon, 12 Aug 2019 09:55:39 +0200
From:   Antoine Tenart <antoine.tenart@...tlin.com>
To:     Matt Pelland <mpelland@...rry.com>
Cc:     Antoine Tenart <antoine.tenart@...tlin.com>,
        netdev@...r.kernel.org, maxime.chevallier@...tlin.com
Subject: Re: [PATCH v2 net-next 2/2] net: mvpp2: support multiple comphy lanes

Hello Matt,

On Fri, Aug 09, 2019 at 06:20:28PM -0400, Matt Pelland wrote:
> On Fri, Aug 09, 2019 at 10:32:50AM +0200, Antoine Tenart wrote:
> > On Thu, Aug 08, 2019 at 07:06:06PM -0400, Matt Pelland wrote:
> > > @@ -5084,14 +5107,38 @@ static int mvpp2_port_probe(struct platform_device *pdev,
> > >  		goto err_free_netdev;
> > >  	}
> > >  
> > > +	port = netdev_priv(dev);
> > > +
> > >  	if (port_node) {
> > > -		comphy = devm_of_phy_get(&pdev->dev, port_node, NULL);
> > > -		if (IS_ERR(comphy)) {
> > > -			if (PTR_ERR(comphy) == -EPROBE_DEFER) {
> > > -				err = -EPROBE_DEFER;
> > > -				goto err_free_netdev;
> > > +		for (i = 0, ncomphys = 0; i < ARRAY_SIZE(port->comphys); i++) {
> > > +			port->comphys[i] = devm_of_phy_get_by_index(&pdev->dev,
> > > +								    port_node,
> > > +								    i);
> > > +			if (IS_ERR(port->comphys[i])) {
> > > +				err = PTR_ERR(port->comphys[i]);
> > > +				port->comphys[i] = NULL;
> > > +				if (err == -EPROBE_DEFER)
> > > +					goto err_free_netdev;
> > > +				err = 0;
> > > +				break;
> > >  			}
> > > -			comphy = NULL;
> > > +
> > > +			++ncomphys;
> > > +		}
> > > +
> > > +		if (phy_mode == PHY_INTERFACE_MODE_XAUI)
> > > +			nrequired_comphys = 4;
> > > +		else if (phy_mode == PHY_INTERFACE_MODE_RXAUI)
> > > +			nrequired_comphys = 2;
> > > +		else
> > > +			nrequired_comphys = 1;
> > > +
> > > +		if (ncomphys < nrequired_comphys) {
> > > +			dev_err(&pdev->dev,
> > > +				"not enough comphys to support %s\n",
> > > +				phy_modes(phy_mode));
> > > +			err = -EINVAL;
> > > +			goto err_free_netdev;
> > 
> > The comphy is optional and could not be described (some SoC do not have
> > a driver for their comphy, and some aren't described at all). In such
> > cases we do rely on the bootloader/firmware configuration. Also, I'm not
> > sure how that would work with dynamic reconfiguration of the mode if the
> > n# of lanes used changes (I'm not sure that is possible though).
> > 
> 
> I'm new to this space, but, from my limited experience it seems unlikely that
> some hardware configuration would require dynamically reconfiguring the number
> of comphy lanes used depending on the phy mode. Unless you disagree, instead of
> removing this check or making things really complicated to support this
> scenario, I propose extending the conditional above to disable sanity checking
> if no comphys were parsed out of the device tree. Something like:
> 
> if (ncomphys != 0 && ncomphys < nrequired_comphys)
> 
> This would cover Maxime's request for sanity checking, which I think is
> valuable, while also maintaining compatibility with platforms that have no
> comphy drivers or some other issue that prevents properly defining comphy nodes
> in the device tree. Does that sound reasonable?

That sounds good.

Thanks!
Antoine

-- 
Antoine Ténart, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com