Re: [PATCH net-next v2 2/7] net: phy: add rxc_always_on flag to phylink_pcs

Hello Russell,

On Tue, 30 Jan 2024, Russell King (Oracle) wrote:
...

quoted

+int phylink_pcs_pre_init(struct phylink *pl, struct phylink_pcs *pcs)
+{
+	int ret = 0;
+
+	/* Signal to PCS driver that MAC requires RX clock for init */
+	if (pl->config->mac_requires_rxc)
+		pcs->rxc_always_on = true;
+
+	if (pcs->ops->pcs_pre_init)
+		ret = pcs->ops->pcs_pre_init(pcs, pl->link_config.interface);

Given that:
1) phylink supports switching between mutliple different interfaces,
2) from what I can see you are only calling this from stmmac's
   initialisation path,
3) you pass the interface mode to the PCS here

then we don't want the PCS to configure itself for the interface mode
passed in, because this function won't be called when the interface
mode changes - and PCS driver authors will have to bear that in mind.
So...

...

However, do we really need it - if the PCS is supplying the RXC to
the MAC, then is the interface mode between the PCS and PHY all that
relevant at this point?

If a PCS can set the needed clock signal without configuring the details 
of a particular link mode, then passing the interface mode to pcs_pre_init() 
would indeed not be relevant. Generally, I agree that setting the interface mode 
shouldn't be the concern of the pre-initialization function. I'll dig a bit 
more into the PCS datasheet and run more tests to see if I can get away with 
enabling the RX clock selectively for this particular PCS model. If not, then 
maybe I can hardcode a "default" interface mode for the pre-initialization that 
will not interfere with the rest of the link setup process.

Best Regards,

-- 
Romain Gantois, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

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