linux-kernel - Re: [PATCH 2/4] net: dsa: add new DSA switch driver for the SMSC-LAN9303

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Message-Id: <201704061542.29859.jbe@pengutronix.de>
Date:   Thu, 6 Apr 2017 15:42:28 +0200
From:   Juergen Borleis <jbe@...gutronix.de>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     kernel@...gutronix.de, f.fainelli@...il.com,
        vivien.didelot@...oirfairelinux.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, davem@...emloft.net
Subject: Re: [PATCH 2/4] net: dsa: add new DSA switch driver for the SMSC-LAN9303

Hi Andrew,

On Thursday 06 April 2017 13:59:00 Andrew Lunn wrote:
> [...]
> > > Does the MDIO bus go to the outside world? Could there be external
> > > PHYs?
> >
> > ???? This device includes two phys (at port 1 and 2) and these
> > functions are called to detect their state.
>
> Some switches have the MDIO bus available on pins. It is then possible
> to connect additional PHYs on the MDIO bus. If their is an external
> MDIO bus, you should remove the test for phy > phy_base + 2, and allow
> the full range of 32.

Hmm, not sure. You can run this device without a master port and use an 
additional external PHY instead. In this case there is an external MDIO 
available to this external PHY. But I don't know if I can reach this MDIO 
in the same way like the internal MDIO to the built-in PHYs.

> [...]
> > > > +		rc = lan9303_phy_reg_write(chip, chip->phy_addr_sel_strap + 1,
> > > > +					   0, BIT(14) | BIT(11));
> > > > +		rc += lan9303_write_switch_reg(chip, LAN9303_MAC_RX_CFG_1,
> > > > +					       0x02);
> > > > +		rc += lan9303_write_switch_reg(chip, LAN9303_MAC_TX_CFG_1,
> > > > +					       0x56);
> > >
> > > It seems odd that port_enable does not touch the PHY, but
> > > port_disable does. What is this doing?
> >
> > My experience is, the framework powers up the phys by its own in
> > conjunction with calling lan9303_port_enable(), but do not power down
> > them in conjunction with calling lan9303_port_disable(). In v2 I do not
> > touch the phy anymore.
>
> So this is touching the BMCR_PDOWN bit? Using the #define would of
> helped explain this.

Okay.

Juergen

-- 
Pengutronix e.K.                             | Juergen Borleis             |
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