linux-kernel - Re: [PATCH v3 1/5] dt-bindings: pci: Add Sophgo SG2042 PCIe host

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Message-ID:
 <BMXPR01MB24403F8CD6BF5D4D2DDC57A4FEFC2@BMXPR01MB2440.INDPRD01.PROD.OUTLOOK.COM>
Date: Wed, 12 Feb 2025 13:54:11 +0800
From: Chen Wang <unicorn_wang@...look.com>
To: Bjorn Helgaas <helgaas@...nel.org>
Cc: Chen Wang <unicornxw@...il.com>, kw@...ux.com,
 u.kleine-koenig@...libre.com, aou@...s.berkeley.edu, arnd@...db.de,
 bhelgaas@...gle.com, conor+dt@...nel.org, guoren@...nel.org,
 inochiama@...look.com, krzk+dt@...nel.org, lee@...nel.org,
 lpieralisi@...nel.org, manivannan.sadhasivam@...aro.org, palmer@...belt.com,
 paul.walmsley@...ive.com, pbrobinson@...il.com, robh@...nel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-pci@...r.kernel.org, linux-riscv@...ts.infradead.org,
 chao.wei@...hgo.com, xiaoguang.xing@...hgo.com, fengchun.li@...hgo.com
Subject: Re: [PATCH v3 1/5] dt-bindings: pci: Add Sophgo SG2042 PCIe host


On 2025/2/12 12:25, Bjorn Helgaas wrote:
[......]
>> pcie_rc1 and pcie_rc2 share registers in cdns_pcie1_ctrl. By using
>> different "sophgo,core-id" values, they can distinguish and access
>> the registers they need in cdns_pcie1_ctrl.
> Where does cdns_pcie1_ctrl fit in this example?  Does that enclose
> both pcie_rc1 and pcie_rc2?

cdns_pcie1_ctrl is defined as a syscon node,  which contains registers 
shared by pcie_rc1 and pcie_rc2. In the binding yaml file, I drew a 
diagram to describe the relationship between them, copy here for your 
quick reference:

+                     +-- Core (Link0) <---> pcie_rc1  +-----------------+
+                     |                                |                 |
+      Cadence IP 2 --+                                | cdns_pcie1_ctrl |
+                     |                                |                 |
+                     +-- Core (Link1) <---> pcie_rc2  +-----------------+

The following is an example with cdns_pcie1_ctrl added. For simplicity, 
I deleted pcie_rc0.

pcie_rc1: pcie@...2000000 {
     compatible = "sophgo,sg2042-pcie-host";
     ...... // host bride level properties
     linux,pci-domain = <1>;
     sophgo,core-id = <0>;
     sophgo,syscon-pcie-ctrl = <&cdns_pcie1_ctrl>;
     port {
         // port level properties
         vendor-id = <0x1f1c>;
         device-id = <0x2042>;
         num-lanes = <2>;
     };
};

pcie_rc2: pcie@...2800000 {
     compatible = "sophgo,sg2042-pcie-host";
     ...... // host bride level properties
     linux,pci-domain = <2>;
     sophgo,core-id = <1>;
     sophgo,syscon-pcie-ctrl = <&cdns_pcie1_ctrl>;
     port {
         // port level properties
         vendor-id = <0x1f1c>;
         device-id = <0x2042>;
         num-lanes = <2>;
     }

};

cdns_pcie1_ctrl: syscon@...3800000 {
     compatible = "sophgo,sg2042-pcie-ctrl", "syscon";
     reg = <0x70 0x63800000 0x0 0x800000>;
};