Re: [PATCH net-next v2 2/3] net: stmmac: Add glue driver for Motorcomm YT6801 ethernet controller

[Xi Ruoyao]

On Sat, 2025-11-15 at 11:46 +0000, Yao Zi wrote:
> On Tue, Nov 11, 2025 at 12:32:56PM +0000, Russell King (Oracle) wrote:
> > On Tue, Nov 11, 2025 at 10:52:51AM +0000, Yao Zi wrote:
> > > +	plat->bus_id		= pci_dev_id(pdev);
> > > +	plat->phy_addr		= -1;
> > > +	plat->phy_interface	= PHY_INTERFACE_MODE_GMII;
> > > +	plat->clk_csr		= STMMAC_CSR_20_35M;
> > 
> > Could you include a comment indicating what the stmmac clock rate
> > actually is (the rate which is used to derive this divider) ? As
> > this is PCI, I'm guessing it's 33MHz, which fits with your divider
> > value.
> 
> The divider is taken from vendor driver, and the clock path isn't
> mentioned in the datasheet, either. I don't think it's 33MHz since
> it's
> a PCIe chip, and there's no 33MHz clock supplied by PCIe.
> 
> The datasheet[1] (Chinese website, requires login) mentions that the
> controller requires a 25MHz external clock input/oscillator to
> function,
> 
> > 25MHz Crystal Input pin.
> > 
> > If use external oscillator or clock from another device.
> >   1. When connect an external 25MHz oscillator or clock from another
> >   device to XTAL_O pin, XTAL_I must be shorted to GND.
> >   2. When connect an external 25MHz oscillator or clock from another
> >   device to XTAL_I pin, keep the XTAL_O floating.
> 
> 25MHz fits in STMMAC_CSR_20_35M, too, so it's more likely the clock
> source.
> 
> I don't think this guess could be confirmed without vendor's help,
> should the information be included as comment.

I used the "beep" function of a multimeter to "probe" the connectivity
of the two YT6801 chips on a XB612B0 V1.1 board.  There are two 25 MHz
oscillators on the board, each connected to a YT6801.

-- 
Xi Ruoyao <xry111@xxxxxxxxxxx>