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

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Message-ID: <CANAwSgR+aaAreZABqXO+0tDW67LnWZzLoU=tXwUi1eN7krceiw@mail.gmail.com>
Date: Thu, 13 Nov 2025 11:46:16 +0530
From: Anand Moon <linux.amoon@...il.com>
To: Manivannan Sadhasivam <mani@...nel.org>
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

Hi Manivannan

On Thu, 13 Nov 2025 at 11:21, Manivannan Sadhasivam <mani@...nel.org> wrote:
>
> 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.
>
Ok, Thanks.
> > > - 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.
>
Ok, got that.
> - Mani
>
> --
> மணிவண்ணன் சதாசிவம்
Thanks
-Anand