Subject: Re: [PATCH v1] net: dsa: qca8k: implement DT-based ports <-> phy translation

From: Christian Lamparter <[email-masked]>
Date: Tue, 05 Feb 2019 13:48:43 +0100

On Tuesday, February 5, 2019 3:45:33 AM CET Andrew Lunn wrote:
> On Mon, Feb 04, 2019 at 10:35:55PM +0100, Christian Lamparter wrote:
> > The QCA8337 enumerates 5 PHYs on the MDC/MDIO access: PHY0-PHY4.
> > Based on the System Block Diagram in Section 1.2 of the
> > QCA8337's datasheet. These PHYs are internally connected
> > to MACs of PORT 1 - PORT 5. However, neither qca8k's slave
> > mdio access functions qca8k_phy_read()/qca8k_phy_write()
> > nor the dsa framework is set up for that.
> > 
> > This version of the patch uses the existing phy-handle
> > properties of each specified DSA Port in the DT to map
> > each PORT/MAC to its exposed PHY on the MDIO bus. This
> > is supported by the current binding document qca8k.txt
> > as well.
> 
> Hi Christian
> 
> Looking at Documentation/devicetree/bindings/net/dsa/qca8k.txt 
> 
> I think everything you need is already implemented. What problem do
> you actually have?

Thankfully, Florian's reply answered the question to me. The problem
has to do with the qca8k's slave qca8k_phy_read and qca8k_phy_write.
Here are the functions:

|qca8k_phy_read(struct dsa_switch *ds, int phy, int regnum)
|{
|	struct qca8k_priv *priv = (struct qca8k_priv *)ds->priv;
|
|	return mdiobus_read(priv->bus, phy, regnum);
|}
|
|static int
|qca8k_phy_write(struct dsa_switch *ds, int phy, int regnum, u16 val)
|{
|	struct qca8k_priv *priv = (struct qca8k_priv *)ds->priv;
|
|	return mdiobus_write(priv->bus, phy, regnum, val);
|}

The trick here is that priv->bus is not the internal
bus instead it's set to the SoC's (external) mii bus in qca8k_sw_probe()).
So this isn't a slave bus! And as stated in the qca8k, the the external
and internal PHY bus are not mapped 1:1.

>From what I can tell from the datasheet, the QCA8337N does have
dedicated MDIO master control register which is what is
needed here. It's at 0x003C. So these mdiobus_read/writes on the
SoCs MDIO bus would either need to be converted to read and write
to 0x003c... Or the qca8k_phy_read() and qca8k_phy_write could be
dropped all together. I've tested it on the WPQ864 and driver
works without since it was never a real slave bus there to begin with.

Thanks,
Christian
---
diff --git a/drivers/net/dsa/qca8k.c b/drivers/net/dsa/qca8k.c
index 7e97e620bd44..a26850c888cf 100644
--- a/drivers/net/dsa/qca8k.c
+++ b/drivers/net/dsa/qca8k.c
@@ -620,22 +620,6 @@ qca8k_adjust_link(struct dsa_switch *ds, int port, struct phy_device *phy)
 	qca8k_port_set_status(priv, port, 1);
 }
 
-static int
-qca8k_phy_read(struct dsa_switch *ds, int phy, int regnum)
-{
-	struct qca8k_priv *priv = (struct qca8k_priv *)ds->priv;
-
-	return mdiobus_read(priv->bus, phy, regnum);
-}
-
-static int
-qca8k_phy_write(struct dsa_switch *ds, int phy, int regnum, u16 val)
-{
-	struct qca8k_priv *priv = (struct qca8k_priv *)ds->priv;
-
-	return mdiobus_write(priv->bus, phy, regnum, val);
-}
-
 static void
 qca8k_get_strings(struct dsa_switch *ds, int port, u32 stringset, uint8_t *data)
 {
@@ -876,8 +860,6 @@ static const struct dsa_switch_ops qca8k_switch_ops = {
 	.setup			= qca8k_setup,
 	.adjust_link            = qca8k_adjust_link,
 	.get_strings		= qca8k_get_strings,
-	.phy_read		= qca8k_phy_read,
-	.phy_write		= qca8k_phy_write,
 	.get_ethtool_stats	= qca8k_get_ethtool_stats,
 	.get_sset_count		= qca8k_get_sset_count,
 	.get_mac_eee		= qca8k_get_mac_eee,