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

[Manivannan Sadhasivam]

On Fri, Nov 28, 2025 at 01:09:06AM +0800, Hans Zhang wrote:
> 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
> 

For the series,

Reviewed-by: Manivannan Sadhasivam <mani at kernel.org>

Bjorn: Could you please take a look? This series has been floating for a
while...

- Mani

> ---
> 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
> 

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