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

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Message-ID: <58b37b3a-7bb7-46bb-8ad4-f4d2f152bf1f@cixtech.com>
Date: Wed, 12 Nov 2025 16:16:20 +0800
From: Hans Zhang <hans.zhang@...tech.com>
To: Mahesh Vaidya <mahesh.vaidya@...era.com>, Hans Zhang
 <18255117159@....com>, lpieralisi@...nel.org, kwilczynski@...nel.org,
 bhelgaas@...gle.com, helgaas@...nel.org, heiko@...ech.de, mani@...nel.org,
 yue.wang@...ogic.com
Cc: pali@...nel.org, neil.armstrong@...aro.org, robh@...nel.org,
 jingoohan1@...il.com, khilman@...libre.com, jbrunet@...libre.com,
 martin.blumenstingl@...glemail.com, cassel@...nel.org,
 linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-amlogic@...ts.infradead.org,
 linux-rockchip@...ts.infradead.org
Subject: Re: [PATCH v6 0/2] PCI: Configure Root Port MPS during host probing



On 11/12/2025 4:06 PM, Mahesh Vaidya wrote:
> [You don't often get email from mahesh.vaidya@...era.com. Learn why this 
> is important at https://aka.ms/LearnAboutSenderIdentification ]
> 
> EXTERNAL EMAIL
> 
> 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@...era.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@....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@....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@....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@....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
>