Hello Florian, Andrew,

On Thu, 28 Jul 2022 14:44:47 -0700
Florian Fainelli [off-list ref] wrote:

On 7/28/22 14:32, Andrew Lunn wrote:

quoted

quoted

+int phy_interface_num_ports(phy_interface_t interface)
+{
+	switch (interface) {
+	case PHY_INTERFACE_MODE_NA:
+	case PHY_INTERFACE_MODE_INTERNAL:
+		return 0;  

I've not yet looked at how this is used. Returning 0 could have
interesting effects i guess? INTERNAL clearly does have some sort of
path between the MAC and the PHY, so i think 1 would be a better
value. NA is less clear, it generally means Don't touch. But again,
there still needs to be a path between the MAC and PHY, otherwise
there would not be any to touch.

Why did you pick 0?  

My reasonning was that PHY_INTERNAL is likely a custom solution to link
IPs existing on the same die, so nothing prevents vendors from
multiplexing links on that interface. But it's a far-fetched
reasonning, so 1 can be good, as other interfaces that are meant to be
used on-die like XGMII.

I would agree that returning 1 is a more sensible default to avoid
breaking users of that function. However this makes me wonder, in
what case will we break the following common meaning:

- Q -> quad
- P -> penta
- O -> octal

Is the helper really needed in the sense that the phy_interface_t
enumeration is explicit enough thanks to or because of its name? --
Florian

Good question actually ! It started as a point from Russell proposing a
helper to get the number of serdes lanes for a given interface, but
this sisn't quite fit the use-case, which was simply to simplify

	if (interface == PHY_INTERFACE_MODE_QSGMII ||
	    interface == PHY_INTERFACE_MODE_QUSGMII)

into

	if (phy_interface_num_ports(interface) == 4)

But this a slim simplification at the cost of a new helper to maintain,
so I can repove that if you want.

Thanks for the reviews,

Maxime