Re: [PATCH v2 1/4] PCI: dwc: Advertise L1 PM Substates only if driver requests it

Frank Li
2025-11-19T00:45:52Z

On Tue, Nov 18, 2025 at 11:45:46PM +0100, Niklas Cassel wrote:
> Hello Frank,
>
> On Tue, Nov 18, 2025 at 05:20:36PM -0500, Frank Li wrote:
> > >
> > > + dw_pcie_hide_unsupported_l1ss(pci);
> > > +
> >
> > Need call dw_pcie_dbi_ro_wr_en(pci) to access PCI_L1SS_CAP.
>
> I disagree.
>
> At least when checking two different versions of the databook
> (one very old and one more recent), the register fields that we
> are touching are all marked as:
>
> Dbi: R/W (sticky)
>

Yes, you are right. Sorry for noise.

Frank

>
> There are some other register fields in PCI_L1SS_CAP, e.g.
> NEXT_OFFSET, CAP_VERSION, and EXTENDED_CAP_ID that are marked as:
>
> Dbi: if (DBI_RO_WR_EN == 1) then R/W(sticky) else R(sticky)
> Note: This register field is sticky.
>
>
> But since we are not touching any of those register fields,
> the current code should be good as is.
>
>
> Perhaps your version of the databook says differently than the
> two versions I have, but considering that they seem to have
> intentionally made these R/W without the need for DBI_RO_WR_EN,
> I don't see a reason why they would want to change it even in
> the absolute newest IP version.
>
>
> Kind regards,
> Niklas