* Rostyslav Khudolii <ros@xxxxxxxx> wrote: > Hi, > > > Rostyslav, I would like to ask you, do you have patches / updates for > > enabling the EnableCf8ExtCfg bit for AMD 17h+ family? I could try to > > adjust my lspci changes for new machines. > > Pali, sorry for the late reply. Do I understand correctly, that even > though you have access to the ECS via > the MMCFG you still want the legacy (direct IO) to work for the > debugging purposes? I can prepare a > simple patch that will allow you to do so if that's the case. > > > > > So what is the practical impact here? Do things start breaking > > unexpectedly if CONFIG_ACPI_MCFG and CONFIG_PCI_MMCONFIG are disabled? > > Then I'd suggest fixing that in the Kconfig space, either by adding a > > dependency on ACPI_MCFG && PCI_MMCONFIG, or by selecting those > > must-have pieces of infrastructure. > > > > Ingo, thank you for the reply. > > The way I understand the access to the PCI ECS (via raw_pci_ext_ops) > works, is the following: > 1. If CONFIG_ACPI_MCFG or CONFIG_PCI_MMCONFIG are enabled - set the > raw_pci_ext_ops to use > MMCFG to access ECS. See pci_mmcfg_early_init() / pci_mmcfg_late_init(); > 2. If CONFIG_ACPI_MCFG and CONFIG_PCI_MMCONFIG are disabled - set the > raw_pci_ext_ops to use > the 'direct' access to ECS. See pci_direct_init(). The direct > access is conditional on the PCI_HAS_IO_ECS > flag being set. > > On AMD, the kernel enables the ECS IO access via the > amd_bus_cpu_online() and pci_enable_pci_io_ecs(). > Except those functions have no desired effect on the AMD 17h+ family > because the register (EnableCf8ExtCfg), > they access, has been moved. What is important though, is that the > PCI_HAS_IO_ECS flag is set unconditionally. > See pci_io_ecs_init() in amd_bus.c > > Therefore I was wondering whether we should add support for the 17h+ > family in those functions to have > the direct access work for those families as well. Yeah, I think so, but I'm really just guessing: > Regarding your suggestion to address this in the Kconfig space - I'm > not quite sure I follow, since right now the kernel will use > raw_pci_ext_ops whenever access beyond the first 256 bytes is > requested. Say we want to make that conditional on CONFIG_ACPI_MCFG > and CONFIG_PCI_MMCONFIG, does it also mean then we want to drop > support for the 'direct' PCI IO ECS access altogether? I thought that enabling CONFIG_ACPI_MCFG would solve the problem, and other architectures are selecting it pretty broadly: arch/arm64/Kconfig: select ACPI_MCFG if (ACPI && PCI) arch/loongarch/Kconfig: select ACPI_MCFG if ACPI arch/riscv/Kconfig: select ACPI_MCFG if (ACPI && PCI) While x86 allows it to be user-configured, which may result in misconfiguration, given that PCI_HAS_IO_ECS is being followed unconditionally if a platform provides it? Thanks, Ingo
