On Wed, Sep 10, 2025 at 12:28:40PM +0000, Verma, Devendra wrote: > > From: Bjorn Helgaas <helgaas@xxxxxxxxxx> [redundant quoted headers removed] > > On Fri, Sep 05, 2025 at 03:46:58PM +0530, Devendra K Verma wrote: > > > AMD MDB PCIe endpoint support. For AMD specific support added the > > > following > > > - AMD supported PCIe Device IDs and Vendor ID (Xilinx). > > > - AMD MDB specific driver data > > > - AMD MDB specific VSEC capability to retrieve the device DDR > > > base address. > > > static void dw_edma_pcie_get_vsec_dma_data(struct pci_dev *pdev, > > > u32 val, map; > > > u16 vsec; > > > u64 off; > > > + u16 vendor; > > > > > > - vsec = pci_find_vsec_capability(pdev, PCI_VENDOR_ID_SYNOPSYS, > > > - DW_PCIE_VSEC_DMA_ID); > > > + vendor = pdev->vendor; > > > + if (vendor != PCI_VENDOR_ID_SYNOPSYS && > > > + vendor != PCI_VENDOR_ID_XILINX) > > > + return; > > > + > > > + vsec = pci_find_vsec_capability(pdev, vendor, > > > + DW_PCIE_VSEC_DMA_ID); > > > > The vendor of a device assigns VSEC IDs and determines what each > > ID means, so the semantics of a VSEC Capability are determined by > > the tuple of (device Vendor ID, VSEC ID), where the Vendor ID is > > the value at 0x00 in config space. > > As AMD is a vendor for this device, it is determined as VSEC > capability to support some of the functionality not supported by the > other vendor Synopsys. Based on your code, the vendor of this device (the value at 0x00 in config space) is either PCI_VENDOR_ID_SYNOPSYS or PCI_VENDOR_ID_XILINX. Whoever controls those Vendor IDs also controls the VSEC ID allocations for those Vendor IDs. > > The DVSEC Capability is a more generic solution to this problem. > > The VSEC ID namespace is determined by the Vendor ID of the > > *device*. > > > > By contrast, the DVSEC ID namespace is determined by a Vendor ID > > in the DVSEC Capability itself, not by the Vendor ID of the > > device. > > > > So AMD could define a DVSEC ID, e.g., 6, and define the semantics > > of that DVSEC. Then devices from *any* vendor could include a > > DVSEC Capability with (PCI_VENDOR_ID_AMD, 6), and generic code > > could look for that DVSEC independent of what is at 0x00 in config > > space. > > As AMD itself becomes the vendor for this device, VSEC capability is > chosen to support the functionality missing in the code. For VSEC, it doesn't matter who *sells* the device or who supplies IP contained in the device. What matters is the Vendor ID at 0x00 in config space. Bjorn
