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

On Wed, May 20, 2026 at 12:09:28AM +0800, Hans Zhang wrote:
> 
> 
> 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/[email protected]/
> """
> 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.
> """
> 

Ok, what about reading the DBI registers very early?

- Mani

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