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

[Niklas Cassel <cassel@kernel.org>]

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)


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