[PATCH v6 0/2] PCI: Configure Root Port MPS during host probing

[Hans Zhang]

On 11/12/2025 4:06 PM, Mahesh Vaidya wrote:
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> On 04-11-2025 22:21, 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)
>> - 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 for v6:
>> - 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).
> Tested this patch series on Agilex 7.
> 
> Tested-by: Mahesh Vaidya <mahesh.vaidya at altera.com>
> 

Hi Mahesh,

Thank you for your test.

Best regards,
Hans

>>
>> Changes for v5:
>> https://patchwork.kernel.org/project/linux-pci/ 
>> patch/20250620155507.1022099-1-18255117159 at 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 at 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 at 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 at 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: 691d401c7e0e5ea34ac6f8151bc0696db1b2500a
>