Re: [PATCH v4] PCI/PTM: Enable PTM only if it advertises a role

[Lukas Wunner <lukas@wunner.de>]

On Tue, Nov 11, 2025 at 09:39:42AM -0600, Bjorn Helgaas wrote:
> I do wonder about the fact that previously we automatically enabled
> PTM only for Root Ports and Switch Upstream Ports, but we didn't
> enable it for Endpoints until a driver called pci_enable_ptm().
> 
> With this change, it looks like we automatically enable PTM for every
> device that supports it.  Worth a mention in the commit log, and we
> might also want to revisit the drivers (ice, idpf, igc, mlx5) that
> explicitly enable it to remove the enable and disable calls there.
> 
> PTM consumes some link bandwidth, so the idea was to avoid paying that
> cost unless a driver actually wanted to use PTM.

pci_pm_suspend() and pci_pm_runtime_suspend() call pci_suspend_ptm()
and there's a code comment preceding the call that it allows platforms
such as Intel Coffee Lake to go to a deeper power state.

So apparently PTM not only has a bandwidth cost but also a power cost.

Thanks,

Lukas