linux-kernel - Re: [PATCH v2] PCI: vmd: Enable PCI PM's L1 substates of remapped PCIe Root Port and NVMe

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Date: Tue, 6 Feb 2024 10:00:57 -0600
From: Bjorn Helgaas <helgaas@...nel.org>
To: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Cc: Jian-Hong Pan <jhp@...lessos.org>, Johan Hovold <johan@...nel.org>,
	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	David Box <david.e.box@...ux.intel.com>,
	Damien Le Moal <dlemoal@...nel.org>,
	Niklas Cassel <cassel@...nel.org>,
	Nirmal Patel <nirmal.patel@...ux.intel.com>,
	Jonathan Derrick <jonathan.derrick@...ux.dev>,
	linux-pci@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
	linux@...lessos.org
Subject: Re: [PATCH v2] PCI: vmd: Enable PCI PM's L1 substates of remapped
 PCIe Root Port and NVMe

On Tue, Feb 06, 2024 at 02:29:12PM +0200, Ilpo Järvinen wrote:
> On Fri, 2 Feb 2024, Jian-Hong Pan wrote:
> ...

> > +out_enable_link_state:
> > +	/*
> > +	 * Make PCI devices at D0 when enable PCI-PM L1 PM Substates from
> > +	 * Section 5.5.4 of PCIe Base Spec Revision 6.0
> 
> I don't understand what are you trying to say here? Are there some typos 
> or grammar errors or something entire missing from the comment?

This is about the fact that per sec 5.5.4, "If setting either or both
of the enable bits for PCI-PM L1 PM Substates, both ports must be
configured as described in this section while in D0."

We can wordsmith this a little, maybe:

  Ensure devices are in D0 before enabling PCI-PM L1 PM Substates, per
  PCIe r6.0, sec 5.5.4.

I look a little askance at having to do this separately from
pci_enable_link_state_locked(), but we can solve that elsewhere if
need be.

> > +	pci_set_power_state_locked(pdev, PCI_D0);
> > +	pci_enable_link_state_locked(pdev, PCIE_LINK_STATE_ALL);