[PATCH v2 1/4] dt-bindings: PCI: rcar-gen4-pci-host: Document optional aux clock

[Manivannan Sadhasivam]

On Mon, May 12, 2025 at 10:42:20PM +0200, Marek Vasut wrote:
> On 5/9/25 9:37 PM, Manivannan Sadhasivam wrote:
> > On Sun, Apr 06, 2025 at 04:45:21PM +0200, Marek Vasut wrote:
> > > Document 'aux' clock which are used to supply the PCIe bus. This
> > > is useful in case of a hardware setup, where the PCIe controller
> > > input clock and the PCIe bus clock are supplied from the same
> > > clock synthesiser, but from different differential clock outputs:
> > 
> > How different is this clock from the 'reference clock'? I'm not sure what you
> > mean by 'PCIe bus clock' here. AFAIK, endpoint only takes the reference clock
> > and the binding already has 'ref' clock for that purpose. So I don't understand
> > how this new clock is connected to the endpoint device.
> 
> See the ASCII art below , CLK_DIF0 is 'ref' clock that feeds the controller
> side, CLK_DIF1 is the bus (or 'aux') clock which feeds the bus (or endpoint)
> side. Both clock come from the same clock synthesizer, but from two separate
> clock outputs of the synthesizer.
> 

Okay. So separate refclks are suppplied to the host and endpoint here and no,
you should not call the other one as 'aux' clock, it is still the refclk. In
this case, you should describe the endpoint refclk in the PCIe bridge node:

		pcie at ... {
			clock = <refclk_host>;
			...

			pcie at 0 {
				device_type = "pci";
				reg = <0x0 0x0 0x0 0x0 0x0>;
				bus-range = <0x01 0xff>;
				clock = <refclk_ep>;
				...
			};
		};


and use the pwrctrl driver PCI_PWRCTRL_SLOT to enable it. Right now, the slot
pwrctrl driver is not handling the refclk, but I can submit a patch for that.

- Mani

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