[RFC PATCH net] net: dsa: mt7530: move PLL setup out of port 6 pad configuration

[Vladimir Oltean]

On Tue, Mar 07, 2023 at 02:26:08PM +0300, Arınç ÜNAL wrote:
> Port 5 as CPU port works fine with this patch. I completely removed from
> port 6 phy modes.
> 
> With your patch on MT7621 (remember port 5 always worked on MT7623):
> 
> - Port 5 at rgmii as the only CPU port works, even though the PLL frequency
> won't be set. The download/upload speed is not affected.

That's good. Empirically it seems to prove that ncpo1 only affects p6,
which was my initial assumption.

> - port 6 at trgmii mode won't work if the PLL frequency is not set. The
> SoC's MAC (gmac0) won't receive anything. It checks out since setting the
> PLL frequency is put under the "Setup the MT7530 TRGMII Tx Clock" comment.
> So port 6 cannot properly transmit frames to the SoC's MAC.
> 
> - Port 6 at rgmii mode works without setting the PLL frequency. Speed is not
> affected.
> 
> I commented out core_write(priv, CORE_PLL_GROUP5,
> RG_LCDDS_PCW_NCPO1(ncpo1)); to stop setting the PLL frequency.
> 
> In conclusion, setting the PLL frequency is only needed for the trgmii mode,
> so I believe we can get rid of it on other cases.

Got it, sounds expected, then? My patch can be submitted as-is, correct?

> One more thing, on MT7621, xtal matches to both HWTRAP_XTAL_40MHZ and
> HWTRAP_XTAL_25MHZ so the final value of ncpo1 is 0x0a00. I'm not sure if
> xtal matching both of them is the expected behaviour.
> 
> > diff --git a/drivers/net/dsa/mt7530.c b/drivers/net/dsa/mt7530.c
> > index fbf27d4ab5d9..12cea89ae0ac 100644
> > --- a/drivers/net/dsa/mt7530.c
> > +++ b/drivers/net/dsa/mt7530.c
> > @@ -439,8 +439,12 @@ mt7530_pad_clk_setup(struct dsa_switch *ds, phy_interface_t interface)
> >  			/* PLL frequency: 150MHz: 1.2GBit */
> >  			if (xtal == HWTRAP_XTAL_40MHZ)
> >  				ncpo1 = 0x0780;
> > +				dev_info(priv->dev, "XTAL is 40MHz, ncpo1 is 0x0780\n");

In the C language, you need to put brackets { } around multi-statement
"if" blocks. Otherwise, despite the indentation, "dev_info" will be
executed unconditionally (unlike in Python for example). There should
also be a warning with newer gcc compilers about the misleading
indentation not leading to the expected code.

Like this:

			if (xtal == HWTRAP_XTAL_40MHZ) {
				ncpo1 = 0x0780;
				dev_info(priv->dev, "XTAL is 40MHz, ncpo1 is 0x0780\n");
			}

> >  			if (xtal == HWTRAP_XTAL_25MHZ)
> >  				ncpo1 = 0x0a00;
> > +				dev_info(priv->dev, "XTAL is 25MHz, ncpo1 is 0x0a00\n");
> > +			if (xtal == HWTRAP_XTAL_20MHZ)
> > +				dev_info(priv->dev, "XTAL is 20MHz too\n");
> >  		} else { /* PLL frequency: 250MHz: 2.0Gbit */
> >  			if (xtal == HWTRAP_XTAL_40MHZ)
> >  				ncpo1 = 0x0c80;
> 
> > [    0.710455] mt7530 mdio-bus:1f: MT7530 adapts as multi-chip module
> > [    0.734419] mt7530 mdio-bus:1f: configuring for fixed/rgmii link mode
> > [    0.741766] mt7530 mdio-bus:1f: Link is Up - 1Gbps/Full - flow control rx/tx
> > [    0.743647] mt7530 mdio-bus:1f: configuring for fixed/trgmii link mode
> > [    0.755422] mt7530 mdio-bus:1f: XTAL is 40MHz, ncpo1 is 0x0780
> > [    0.761250] mt7530 mdio-bus:1f: XTAL is 25MHz, ncpo1 is 0x0a00
> > [    0.769414] mt7530 mdio-bus:1f: Link is Up - 1Gbps/Full - flow control rx/tx
> > [    0.772067] mt7530 mdio-bus:1f lan1 (uninitialized): PHY [mt7530-0:00] driver [MediaTek MT7530 PHY] (irq=17)
> > [    0.788647] mt7530 mdio-bus:1f lan2 (uninitialized): PHY [mt7530-0:01] driver [MediaTek MT7530 PHY] (irq=18)
> > [    0.800354] mt7530 mdio-bus:1f lan3 (uninitialized): PHY [mt7530-0:02] driver [MediaTek MT7530 PHY] (irq=19)
> > [    0.812031] mt7530 mdio-bus:1f lan4 (uninitialized): PHY [mt7530-0:03] driver [MediaTek MT7530 PHY] (irq=20)
> > [    0.823418] mtk_soc_eth 1e100000.ethernet eth1: entered promiscuous mode
> > [    0.830250] mtk_soc_eth 1e100000.ethernet eth0: entered promiscuous mode
> > [    0.837007] DSA: tree 0 setup
> 
> Thunderbird limits lines to about 72 columns, so I'm pasting as quotation
> which seems to bypass that.

That seems to have worked, but shouldn't have been needed. I've uninstalled
Thunderbird in favor of mutt + vim for email editing.. although, isn't
there a Word Wrap option which you can just turn off?