linux-kernel - Re: [PATCH v15 0/6] Refactor capability search into common macros

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Message-ID: <39e654cfcce848d57671cbd5d7038f2f9667789a.camel@linux.ibm.com>
Date: Thu, 14 Aug 2025 10:32:02 +0200
From: Niklas Schnelle <schnelle@...ux.ibm.com>
To: Hans Zhang <18255117159@....com>, lpieralisi@...nel.org,
        kwilczynski@...nel.org, bhelgaas@...gle.com, helgaas@...nel.org,
        jingoohan1@...il.com, mani@...nel.org
Cc: robh@...nel.org, ilpo.jarvinen@...ux.intel.com, gbayer@...ux.ibm.com,
        lukas@...ner.de, arnd@...nel.org, geert@...ux-m68k.org,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v15 0/6] Refactor capability search into common macros

On Wed, 2025-08-13 at 22:45 +0800, Hans Zhang wrote:
> Dear Maintainers,
> 
> This patch series addresses long-standing code duplication in PCI
> capability discovery logic across the PCI core and controller drivers.
> The existing implementation ties capability search to fully initialized
> PCI device structures, limiting its usability during early controller
> initialization phases where device/bus structures may not yet be
> available.
> 
> The primary goal is to decouple capability discovery from PCI device
> dependencies by introducing a unified framework using config space
> accessor-based macros. This enables:
> 
> 1. Early Capability Discovery: Host controllers (e.g., Cadence, DWC)
> can now perform capability searches during pre-initialization stages
> using their native config accessors.
> 
> 2. Code Consolidation: Common logic for standard and extended capability
> searches is refactored into shared macros (`PCI_FIND_NEXT_CAP` and
> `PCI_FIND_NEXT_EXT_CAP`), eliminating redundant implementations.
> 
> 3. Safety and Maintainability: TTL checks are centralized within the
> macros to prevent infinite loops, while hardcoded offsets in drivers
> are replaced with dynamic discovery, reducing fragility.
> 
> Key improvements include:  
> - Driver Conversions: DesignWare and Cadence drivers are migrated to
>   use the new macros, removing device-specific assumptions and ensuring
>   consistent error handling.
> 
> - Enhanced Readability: Magic numbers are replaced with symbolic
>   constants, and config space accessors are standardized for clarity.
> 
> - Backward Compatibility: Existing PCI core behavior remains unchanged.
> 
> ---
> Dear Niklas and Gerd,
> 
> Can you test this series of patches on the s390?
> 
> Thank you very much.

Hi Hans, I gave this series a try on top of v6.17-rc1 on s390
and a bunch of PCI devices including the mlx5 cards that Gerd we
originally saw issues with. All looks well now. So feel free to
add as appropriate:

Tested-by: Niklas Schnelle <schnelle@...ux.ibm.com>

Thanks,
Niklas