Re: [PATCH 0/3] PCI: dwc: Cache PCIe capability offset and simplify drivers

From: Manivannan Sadhasivam <mani@kernel.org>
To: Hans Zhang <18255117159@163.com>
Cc: bhelgaas@google.com, lpieralisi@kernel.org,
	kwilczynski@kernel.org,  jingoohan1@gmail.com,
	mx@lists.linux.dev, linuxppc-dev@lists.ozlabs.org,
	 linux-amlogic@lists.infradead.org,
	linux-rockchip@lists.infradead.org,
	 linux-arm-msm@vger.kernel.org, sophgo@lists.linux.dev,
	linux-riscv@lists.infradead.org,  spacemit@lists.linux.dev,
	linux-tegra@vger.kernel.org, linux-pci@vger.kernel.org,
	 linux-kernel@vger.kernel.org
Subject: Re: [PATCH 0/3] PCI: dwc: Cache PCIe capability offset and simplify drivers
Date: Tue, 19 May 2026 19:27:53 +0530	[thread overview]
Message-ID: <beqy5ykxgo4ianya6r4mahkkyujs6lly475u26vqaemgqsdnhp@2pn5ipczwc34> (raw)
In-Reply-To: <20260509135152.2241235-1-18255117159@163.com>

On Sat, May 09, 2026 at 09:51:49PM +0800, Hans Zhang wrote:
> The DWC PCIe core and its many platform drivers repeatedly call
> dw_pcie_find_capability(pci, PCI_CAP_ID_EXP) to obtain the offset of the
> PCI Express Capability structure. This is wasteful and makes the code
> verbose. And some even search for the PCI_CAP_ID_EXP offset value within
> the suspend/resume functions.
> 

Sashiko has flagged some real issues with this series in accessing DBI space
very early and 'pci->pcie_cap' being 0.

Those needs to be fixed.

- Mani

> Add a cached pcie_cap field in struct dw_pcie and a helper
> dw_pcie_get_pcie_cap() to initialize it once at probe time. Then replace
> all explicit capability searches with the cached value across the
> entire dwc subtree.
> 
> Hans Zhang (3):
>   PCI: dwc: Add pcie_cap field and helper in designware header
>   PCI: dwc: Use cached PCIe capability offset in core
>   PCI: dwc: Simplify platform drivers using cached capability offset
> 
>  drivers/pci/controller/dwc/pci-imx6.c         |  6 +--
>  .../pci/controller/dwc/pci-layerscape-ep.c    |  4 +-
>  drivers/pci/controller/dwc/pci-meson.c        |  4 +-
>  .../pci/controller/dwc/pcie-designware-ep.c   |  4 +-
>  .../pci/controller/dwc/pcie-designware-host.c |  4 +-
>  drivers/pci/controller/dwc/pcie-designware.c  | 16 +++---
>  drivers/pci/controller/dwc/pcie-designware.h  | 17 +++++++
>  drivers/pci/controller/dwc/pcie-dw-rockchip.c | 15 +++---
>  drivers/pci/controller/dwc/pcie-eswin.c       |  3 +-
>  drivers/pci/controller/dwc/pcie-fu740.c       |  2 +-
>  drivers/pci/controller/dwc/pcie-intel-gw.c    |  2 +-
>  drivers/pci/controller/dwc/pcie-qcom-ep.c     | 11 ++--
>  drivers/pci/controller/dwc/pcie-qcom.c        | 24 ++++-----
>  drivers/pci/controller/dwc/pcie-sophgo.c      |  8 ++-
>  drivers/pci/controller/dwc/pcie-spacemit-k1.c |  5 +-
>  drivers/pci/controller/dwc/pcie-spear13xx.c   |  6 +--
>  drivers/pci/controller/dwc/pcie-tegra194.c    | 51 +++++++------------
>  17 files changed, 85 insertions(+), 97 deletions(-)
> 
> 
> base-commit: 70390501d1944d4e5b8f7352be180fceb3a44132
> -- 
> 2.34.1
> 

-- 
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