[PATCH v7 0/2] PCI: Configure Root Port MPS during host probing

Hans Zhang
2025-11-27T17:10:16Z

Current PCIe initialization exhibits a key optimization gap: Root Ports
may operate with non-optimal Maximum Payload Size (MPS) settings. While
downstream device configuration is handled during bus enumeration, Root
Port MPS values inherited from firmware or hardware defaults often fail
to utilize the full capabilities supported by controller hardware. This
results in suboptimal data transfer efficiency throughout the PCIe
hierarchy.

This patch series addresses this by:

1. Core PCI enhancement (Patch 1):
- Proactively configures Root Port MPS during host controller probing
- Sets initial MPS to hardware maximum (128 << dev->pcie_mpss)
- Conditional on PCIe bus tuning being enabled (PCIE_BUS_TUNE_OFF unset)
and not in PCIE_BUS_PEER2PEER mode (which requires default 128 bytes)
- Maintains backward compatibility via PCIE_BUS_TUNE_OFF check
- Preserves standard MPS negotiation during downstream enumeration

2. Driver cleanup (Patch 2):
- Removes redundant MPS configuration from Meson PCIe controller driver
- Functionality is now centralized in PCI core
- Simplifies driver maintenance long-term

---
Changes in v7:
- Exclude PCIE_BUS_PEER2PEER mode from Root Port MPS configuration
- Remove redundant check for upstream bridge (Root Ports don't have one)
- Improve commit message and code comments as per Bjorn.

Changes for v6:
https://patchwork.kernel.org/project/linux-pci/patch/20251104165125.174168-1-18255117159@163.com/

- Modify the commit message and comments. (Bjorn)
- Patch 1/2 code logic: Add !bridge check to configure MPS only for Root Ports
without an upstream bridge (root bridges), avoiding incorrect handling of
non-root-bridge Root Ports (Niklas).

Changes for v5:
https://patchwork.kernel.org/project/linux-pci/patch/20250620155507.1022099-1-18255117159@163.com/

- Use pcie_set_mps directly instead of pcie_write_mps.
- The patch 1 commit message were modified.

Changes for v4:
https://patchwork.kernel.org/project/linux-pci/patch/20250510155607.390687-1-18255117159@163.com/

- The patch [v4 1/2] add a comment to explain why it was done this way.
- The patch [v4 2/2] have not been modified.
- Drop patch [v3 3/3]. The Maintainer of the pci-aardvark.c file suggests
that this patch cannot be submitted. In addition, Mani also suggests
dropping this patch until this series of issues is resolved.

Changes for v3:
https://patchwork.kernel.org/project/linux-pci/patch/20250506173439.292460-1-18255117159@163.com/

- The new split is patch 2/3 and 3/3.
- Modify the patch 1/3 according to Niklas' suggestion.

Changes for v2:
https://patchwork.kernel.org/project/linux-pci/patch/20250425095708.32662-1-18255117159@163.com/

- According to the Maintainer's suggestion, limit the setting of MPS
changes to platforms with controller drivers.
- Delete the MPS code set by the SOC manufacturer.
---

Hans Zhang (2):
PCI: Configure Root Port MPS during host probing
PCI: dwc: Remove redundant MPS configuration

drivers/pci/controller/dwc/pci-meson.c | 17 -----------------
drivers/pci/probe.c | 12 ++++++++++++
2 files changed, 12 insertions(+), 17 deletions(-)

base-commit: 765e56e41a5af2d456ddda6cbd617b9d3295ab4e
--
2.34.1