linux-kernel - Re: [PATCH v2 01/21] arm64: dts: qcom: sm8250: Add PCIe bridge node

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Message-ID: <20250105101612.t6c4pw5uxhb5rdde@thinkpad>
Date: Sun, 5 Jan 2025 15:46:12 +0530
From: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To: Bjorn Helgaas <helgaas@...nel.org>, Rob Herring <robh+dt@...nel.org>,
	Rob Herring <robh@...nel.org>
Cc: Bjorn Andersson <andersson@...nel.org>,
	Konrad Dybcio <konrad.dybcio@...aro.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
	Conor Dooley <conor+dt@...nel.org>,
	cros-qcom-dts-watchers@...omium.org, linux-arm-msm@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 01/21] arm64: dts: qcom: sm8250: Add PCIe bridge node

Hi Bjorn,

On Fri, Jan 03, 2025 at 03:05:31PM -0600, Bjorn Helgaas wrote:
> On Thu, Mar 21, 2024 at 04:46:21PM +0530, Manivannan Sadhasivam wrote:
> > On Qcom SoCs, the PCIe host bridge is connected to a single PCIe bridge
> > for each controller instance. Hence, add a node to represent the bridge.
> > 
> > Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
> > ---
> >  arch/arm64/boot/dts/qcom/sm8250.dtsi | 30 ++++++++++++++++++++++++++++++
> >  1 file changed, 30 insertions(+)
> > 
> > diff --git a/arch/arm64/boot/dts/qcom/sm8250.dtsi b/arch/arm64/boot/dts/qcom/sm8250.dtsi
> > index 39bd8f0eba1e..fe5485256b22 100644
> > --- a/arch/arm64/boot/dts/qcom/sm8250.dtsi
> > +++ b/arch/arm64/boot/dts/qcom/sm8250.dtsi
> > @@ -2203,6 +2203,16 @@ pcie0: pcie@...0000 {
> >  			dma-coherent;
> >  
> >  			status = "disabled";
> > +
> > +			pcie@0 {
> > +				device_type = "pci";
> > +				reg = <0x0 0x0 0x0 0x0 0x0>;
> > +				bus-range = <0x01 0xff>;
> 
> Hi Mani, most or all of the patches in this series add this
> "bus-range" property.  IIUC, these are all Root Ports and hence the
> secondary/subordinate bus numbers should be programmable.
> 

Right. It is not a functional dependency.

> If that's the case, I don't think we need to include "bus-range" in DT
> for them, do we?
> 

We mostly include it to silence the below bindings check for the endpoint device
node:

Warning (pci_device_bus_num): /soc@...cie@...0000/pcie@...ifi@0: PCI bus number 1 out of range, expected (0 - 0)

DTC check is happy if the 'bus-range' property is absent in the bridge node. But
while validating the endpoint node (if defined), it currently relies on the
parent 'bus-range' property to verify the bus number provided in the endpoint
'reg' property.

I don't know else the check can verify the correctness of the endpoint bus
number. So deferring to Rob here.

- Mani

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