linux-kernel - Re: [PATCH v2] schemas: pci: Document PCIe T_POWER

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Message-ID: <vnfjiakbgw3s7dxqh3zriifxjoqcjhshat3hrnikebpa57yh3k@erc4nb5enqes>
Date: Thu, 13 Nov 2025 11:20:56 +0530
From: Manivannan Sadhasivam <mani@...nel.org>
To: Anand Moon <linux.amoon@...il.com>
Cc: Lukas Wunner <lukas@...ner.de>, 
	Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>, andersson@...nel.org, robh@...nel.org, 
	manivannan.sadhasivam@...aro.org, krzk@...nel.org, helgaas@...nel.org, 
	linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org, lpieralisi@...nel.org, kw@...ux.com, 
	conor+dt@...nel.org, linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org, 
	devicetree-spec@...r.kernel.org, quic_vbadigan@...cinc.com
Subject: Re: [PATCH v2] schemas: pci: Document PCIe T_POWER_ON

On Thu, Nov 13, 2025 at 10:46:59AM +0530, Anand Moon wrote:
> Hi Manivannan
> 
> On Thu, 13 Nov 2025 at 10:01, Manivannan Sadhasivam <mani@...nel.org> wrote:
> >
> > On Mon, Nov 10, 2025 at 01:41:45PM +0100, Lukas Wunner wrote:
> > > On Mon, Nov 10, 2025 at 04:59:47PM +0530, Krishna Chaitanya Chundru wrote:
> > > > From PCIe r6, sec 5.5.4 & Table 5-11 in sec 5.5.5 T_POWER_ON is the
> > >
> > > Please use the latest spec version as reference, i.e. PCIe r7.0.
> > >
> > > > minimum amount of time(in us) that each component must wait in L1.2.Exit
> > > > after sampling CLKREQ# asserted before actively driving the interface to
> > > > ensure no device is ever actively driving into an unpowered component and
> > > > these values are based on the components and AC coupling capacitors used
> > > > in the connection linking the two components.
> > > >
> > > > This property should be used to indicate the T_POWER_ON for each Root Port.
> > >
> > > What's the difference between this property and the Port T_POWER_ON_Scale
> > > and T_POWER_ON_Value in the L1 PM Substates Capabilities Register?
> > >
> > > Why do you need this in the device tree even though it's available
> > > in the register?
> > >
> >
> > Someone needs to program these registers. In the x86 world, BIOS will do it
> > happily, but in devicetree world, OS has to do it. And since this is a platform
> > specific value, this is getting passed from devicetree.
> >
> According to the RK3588 TRM Part 2, the DSP_PCIE_L1SUB_CAPABILITY_REG (0x4)
> It is a commonly configurable parameter, It can be tuned on for the
> Rockchip platform.

T_POWER_ON is a generic value defined in the spec. All compatible platforms
should support setting this value through 'L1 PM Substates Capabilities'
register or by platform specific register.

> > - Mani
> >
> > --
> > மணிவண்ணன் சதாசிவம்
> >
> Thanks
> -Anand
> 
> I could not apply this patch
> 
> $ git am ./v2_20251110_krishna_chundru_schemas_pci_document_pcie_t_power_on.mbx
> Applying: schemas: pci: Document PCIe T_POWER_ON
> error: dtschema/schemas/pci/pci-bus-common.yaml: does not exist in index
> Patch failed at 0001 schemas: pci: Document PCIe T_POWER_ON
> hint: Use 'git am --show-current-patch=diff' to see the failed patch
> hint: When you have resolved this problem, run "git am --continue".
> hint: If you prefer to skip this patch, run "git am --skip" instead.
> hint: To restore the original branch and stop patching, run "git am --abort".
> hint: Disable this message with "git config set advice.mergeConflict false"

This is a dtschema patch, not Linux kernel.

- Mani

-- 
மணிவண்ணன் சதாசிவம்