linux-kernel - Re: [PATCH v6 01/11] arm64: dts: imx95-15x15-evk: Add supports-clkreq property to PCIe M.2 port

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Message-ID: <aRPn89vIkmije-Ks@dragon>
Date: Wed, 12 Nov 2025 09:50:43 +0800
From: Shawn Guo <shawnguo2@...h.net>
To: Frank Li <Frank.li@....com>, "robh@...nel.org" <robh@...nel.org>
Cc: Hongxing Zhu <hongxing.zhu@....com>,
	"l.stach@...gutronix.de" <l.stach@...gutronix.de>,
	"lpieralisi@...nel.org" <lpieralisi@...nel.org>,
	"kwilczynski@...nel.org" <kwilczynski@...nel.org>,
	"mani@...nel.org" <mani@...nel.org>,
	"krzk+dt@...nel.org" <krzk+dt@...nel.org>,
	"conor+dt@...nel.org" <conor+dt@...nel.org>,
	"bhelgaas@...gle.com" <bhelgaas@...gle.com>,
	"shawnguo@...nel.org" <shawnguo@...nel.org>,
	"s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
	"kernel@...gutronix.de" <kernel@...gutronix.de>,
	"festevam@...il.com" <festevam@...il.com>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"imx@...ts.linux.dev" <imx@...ts.linux.dev>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 01/11] arm64: dts: imx95-15x15-evk: Add
 supports-clkreq property to PCIe M.2 port

On Tue, Nov 11, 2025 at 11:10:05AM -0500, Frank Li wrote:
> On Tue, Nov 11, 2025 at 08:02:35AM +0000, Hongxing Zhu wrote:
> > > -----Original Message-----
> > > From: Shawn Guo <shawnguo2@...h.net>
> > > Sent: 2025年11月11日 15:11
> > > To: Hongxing Zhu <hongxing.zhu@....com>
> > > Cc: Frank Li <frank.li@....com>; l.stach@...gutronix.de;
> > > lpieralisi@...nel.org; kwilczynski@...nel.org; mani@...nel.org;
> > > robh@...nel.org; krzk+dt@...nel.org; conor+dt@...nel.org;
> > > bhelgaas@...gle.com; shawnguo@...nel.org; s.hauer@...gutronix.de;
> > > kernel@...gutronix.de; festevam@...il.com; linux-pci@...r.kernel.org;
> > > linux-arm-kernel@...ts.infradead.org; devicetree@...r.kernel.org;
> > > imx@...ts.linux.dev; linux-kernel@...r.kernel.org
> > > Subject: Re: [PATCH v6 01/11] arm64: dts: imx95-15x15-evk: Add
> > > supports-clkreq property to PCIe M.2 port
> > >
> > > On Wed, Oct 15, 2025 at 11:04:18AM +0800, Richard Zhu wrote:
> > > > According to PCIe r6.1, sec 5.5.1.
> > > >
> > > > The following rules define how the L1.1 and L1.2 substates are entered:
> > > > Both the Upstream and Downstream Ports must monitor the logical state
> > > > of the CLKREQ# signal.
> > > >
> > > > Typical implement is using open drain, which connect RC's clkreq# to
> > > > EP's clkreq# together and pull up clkreq#.
> > > >
> > > > imx95-15x15-evk matches this requirement, so add supports-clkreq to
> > > > allow PCIe device enter ASPM L1 Sub-State.
> > > >
> > > > Signed-off-by: Richard Zhu <hongxing.zhu@....com>
> > > > ---
> > > >  arch/arm64/boot/dts/freescale/imx95-15x15-evk.dts | 1 +
> > > >  1 file changed, 1 insertion(+)
> > > >
> > > > diff --git a/arch/arm64/boot/dts/freescale/imx95-15x15-evk.dts
> > > > b/arch/arm64/boot/dts/freescale/imx95-15x15-evk.dts
> > > > index 148243470dd4a..3ee032c154fa3 100644
> > > > --- a/arch/arm64/boot/dts/freescale/imx95-15x15-evk.dts
> > > > +++ b/arch/arm64/boot/dts/freescale/imx95-15x15-evk.dts
> > > > @@ -556,6 +556,7 @@ &pcie0 {
> > > >  	pinctrl-names = "default";
> > > >  	reset-gpio = <&gpio5 13 GPIO_ACTIVE_LOW>;
> > > >  	vpcie-supply = <&reg_m2_pwr>;
> > > > +	supports-clkreq;
> > >
> > > Is binding updated for this property?
> > >
> > > Shawn
> > >
> > Hi Shawn:
> > As I know that It's a documented binding property as below.
> > - supports-clkreq:
> >    If present this property specifies that CLKREQ signal routing exists from
> >    root port to downstream device and host bridge drivers can do programming
> >    which depends on CLKREQ signal existence. For example, programming root port
> >    not to advertise ASPM L1 Sub-States support if there is no CLKREQ signal.
> > ./Documentation/devicetree/bindings/pci/pci.txt
> 
> Shawn:
> 
> 	This file should be removed. It is already merge to Rob's dt-scheme
> as PCIe standard properties.
> 
> See: https://github.com/devicetree-org/dt-schema/blob/main/dtschema/schemas/pci/pci-bus-common.yaml

Ah, thanks!

Rob,

So it's no longer the case that kernel Documentation/devicetree/bindings
has all bindings documentation?  Or it's never been the case?  I used to
grep a property in the folder to see if it's documented or not.

Shawn