On Thu, Nov 18, 2021 at 02:03:34PM +0200, Vladimir Oltean wrote:

On Wed, Nov 17, 2021 at 11:50:50PM +0100, Marek Behún wrote:

quoted

+static int mv3310_select_mactype(unsigned long *interfaces)
+{
+	if (test_bit(PHY_INTERFACE_MODE_USXGMII, interfaces))
+		return MV_V2_33X0_PORT_CTRL_MACTYPE_USXGMII;
+	else if (test_bit(PHY_INTERFACE_MODE_SGMII, interfaces) &&
+		 test_bit(PHY_INTERFACE_MODE_10GBASER, interfaces))
+		return MV_V2_33X0_PORT_CTRL_MACTYPE_10GBASER;
+	else if (test_bit(PHY_INTERFACE_MODE_SGMII, interfaces) &&
+		 test_bit(PHY_INTERFACE_MODE_RXAUI, interfaces))
+		return MV_V2_33X0_PORT_CTRL_MACTYPE_RXAUI;
+	else if (test_bit(PHY_INTERFACE_MODE_SGMII, interfaces) &&
+		 test_bit(PHY_INTERFACE_MODE_XAUI, interfaces))
+		return MV_V2_3310_PORT_CTRL_MACTYPE_XAUI;
+	else if (test_bit(PHY_INTERFACE_MODE_10GBASER, interfaces))
+		return MV_V2_33X0_PORT_CTRL_MACTYPE_10GBASER_RATE_MATCH;
+	else if (test_bit(PHY_INTERFACE_MODE_RXAUI, interfaces))
+		return MV_V2_33X0_PORT_CTRL_MACTYPE_RXAUI_RATE_MATCH;
+	else if (test_bit(PHY_INTERFACE_MODE_XAUI, interfaces))
+		return MV_V2_3310_PORT_CTRL_MACTYPE_XAUI_RATE_MATCH;
+	else if (test_bit(PHY_INTERFACE_MODE_SGMII, interfaces))
+		return MV_V2_33X0_PORT_CTRL_MACTYPE_10GBASER;
+	else
+		return -1;
+}
+

I would like to understand this heuristic better. Both its purpose and
its implementation.

It says:
(a) If the intersection between interface modes supported by the MAC and
    the PHY contains USXGMII, then use USXGMII as a MACTYPE
(b) Otherwise, if the intersection contains both 10GBaseR and SGMII, then
    use 10GBaseR as MACTYPE
(...)
(c) Otherwise, if the intersection contains just 10GBaseR (no SGMII), then
    use 10GBaseR with rate matching as MACTYPE
(...)
(d) Otherwise, if the intersection contains just SGMII (no 10GBaseR), then
    use 10GBaseR as MACTYPE (no rate matching).

What is likely confusing you is a misinterpretation of the constant.
MV_V2_33X0_PORT_CTRL_MACTYPE_10GBASER actually means the PHY will
choose between 10GBASE-R, 5GBASE-R, 2500BASE-X, and SGMII depending
on the speed negotiated by the media. In this setting, the PHY
dictates which interface mode will be used.

I could have named "MV_V2_33X0_PORT_CTRL_MACTYPE_10GBASER" as
"MV_V2_33X0_PORT_CTRL_MACTYPE_10GBASER_5GBASER_2500BASEX_SGMII_AUTONEG_ON".
Similar with "MV_V2_33X0_PORT_CTRL_MACTYPE_10GBASER_NO_SGMII_AN", which
would be
"MV_V2_33X0_PORT_CTRL_MACTYPE_10GBASER_5GBASER_2500BASEX_SGMII_AUTONEG_OFF".
And "MV_V2_3310_PORT_CTRL_MACTYPE_XAUI" would be
"MV_V2_3310_PORT_CTRL_MACTYPE_XAUI_5GBASER_2500BASEX_SGMII_AUTONEG_ON".

Clearly using such long identifiers would have been rediculous,
especially the second one at 74 characters.

First of all, what is MACTYPE exactly? And what is the purpose of
changing it? What would happen if this configuration remained fixed, as
it were?

The PHY defines the MAC interface mode depending on the MACTYPE
setting selected and the results of the media side negotiation.

I think the above answers your remaining questions.

-- 
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