Re: [PATCH 1/2] PCI: Write RCB only when it changes

[Stefan Roese]

Hi Håkon,

On 30 Sep 2026, at 16:41, Haakon Bugge wrote:
> Since an unconditional write to Link Control while programming RCB
> does not violate the PCIe specification, this appears to be
> device-specific behavior and should be handled with a device quirk
> instead.

You're right that the RCB write itself is legal. What is not legal is
the state it leaves behind: ASPM L0s/L1 enabled on a link whose Root
Port supports no ASPM (r7.0, sec 5.4.1.4, as Bjorn pointed out).
pcie_aspm_cap_init() returns early for such a link and never clears
ASPM Control, so this is not specific to one device.

I did look at a quirk. The existing helper, pcie_aspm_remove_cap(),
only clears the support flags, which leads into the same early return
and leaves ASPM Control set. A quirk that clears it would have to
repeat the aspm.c link checks. So v2 will fix this in aspm.c, and
keep only Bjorn's set-only RCB change in probe.c.

Thanks,
Stefan