linux-kernel - Re: [PATCH v6 10/10] arm64: dts: imx95: Add ref clock for i.MX95 PCIe

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Message-ID: <20241122171340.4uwlddrwadg3vyz4@thinkpad>
Date: Fri, 22 Nov 2024 22:43:40 +0530
From: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To: Frank Li <Frank.li@....com>
Cc: Richard Zhu <hongxing.zhu@....com>, l.stach@...gutronix.de,
	bhelgaas@...gle.com, lpieralisi@...nel.org, kw@...ux.com,
	robh@...nel.org, krzk+dt@...nel.org, conor+dt@...nel.org,
	shawnguo@...nel.org, s.hauer@...gutronix.de, festevam@...il.com,
	imx@...ts.linux.dev, kernel@...gutronix.de,
	linux-pci@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 10/10] arm64: dts: imx95: Add ref clock for i.MX95 PCIe

On Fri, Nov 15, 2024 at 12:28:50PM -0500, Frank Li wrote:
> On Fri, Nov 15, 2024 at 12:46:05PM +0530, Manivannan Sadhasivam wrote:
> > On Fri, Nov 01, 2024 at 03:06:10PM +0800, Richard Zhu wrote:
> > > Add ref clock for i.MX95 PCIe here, when the internal PLL is used as
> > > PCIe reference clock.
> > >
> > > Signed-off-by: Richard Zhu <hongxing.zhu@....com>
> > > Reviewed-by: Frank Li <Frank.Li@....com>
> > > ---
> > >  arch/arm64/boot/dts/freescale/imx95.dtsi | 18 ++++++++++++++----
> > >  1 file changed, 14 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/arch/arm64/boot/dts/freescale/imx95.dtsi b/arch/arm64/boot/dts/freescale/imx95.dtsi
> > > index 03661e76550f..5cb504b5f851 100644
> > > --- a/arch/arm64/boot/dts/freescale/imx95.dtsi
> > > +++ b/arch/arm64/boot/dts/freescale/imx95.dtsi
> > > @@ -1473,6 +1473,14 @@ smmu: iommu@...d0000 {
> > >  			};
> > >  		};
> > >
> > > +		hsio_blk_ctl: syscon@...100c0 {
> > > +			compatible = "nxp,imx95-hsio-blk-ctl", "syscon";
> > > +			reg = <0x0 0x4c0100c0 0x0 0x4>;
> > > +			#clock-cells = <1>;
> > > +			clocks = <&dummy>;
> >
> > What does this 'dummy' clock do? Looks like it doesn't have a frequency at all.
> > Is bootloader updating it? But the name looks wierd.
> 
> dummy clock is not used for this instance, which needn't at all. Leave here
> just keep compatible with the other instance.
> 
> Some instance of "nxp,imx95-hsio-blk-ctl" required input clocks. but this
> one is not, so put dummy here.
> 

DT should describe the hardware and hardware cannot have dummy clock. If the IP
requires a clock, then pass relevant clock (even if it is a fixed-clock).

- Mani

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