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

[Hans Zhang <18255117159@163.com>]

On 5/19/26 21:57, Manivannan Sadhasivam wrote:
> 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.


Hi Mani,

We have discussed this issue in the Cadence driver. I think it won't 
cause any problems. Specifically as follows:

https://lore.kernel.org/linux-pci/5823faec-d972-4c77-90ec-a215c686e0a8@163.com/
"""
As per PCIe r7.0, sec 7.5.1.1.11, Since all PCI Express Functions are 
required to implement the PCI Express Capability structure, which
must be included somewhere in this linked list.
"""



Bjorn also responded as follows:
https://lore.kernel.org/linux-pci/20260505212306.GA744158@bhelgaas/
"""
It's true that all Root Ports must have a PCIe Capability.
"""



Mani, should I continue to make the judgment that 'pci->pcie_cap' might 
be 0 as per your instructions?



Best regards,
Hans


> 
> 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
>>
>