linux-kernel - Re: [PATCH 1/4] PCI/PTM: Preserve PTM Root Select

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Message-ID: <20220902233233.GA390494@bhelgaas>
Date:   Fri, 2 Sep 2022 18:32:33 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
Cc:     Kai-Heng Feng <kai.heng.feng@...onical.com>,
        Rajvi Jingar <rajvi.jingar@...ux.intel.com>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Koba Ko <koba.ko@...onical.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        "David E . Box" <david.e.box@...ux.intel.com>,
        linux-pci@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Bjorn Helgaas <bhelgaas@...gle.com>
Subject: Re: [PATCH 1/4] PCI/PTM: Preserve PTM Root Select

On Fri, Sep 02, 2022 at 02:11:12PM -0700, Sathyanarayanan Kuppuswamy wrote:
> On 9/2/22 1:38 PM, Bjorn Helgaas wrote:
> > On Fri, Sep 02, 2022 at 10:24:05AM -0700, Sathyanarayanan Kuppuswamy wrote:
> >> On 9/2/22 7:58 AM, Bjorn Helgaas wrote:
> >>> From: Bjorn Helgaas <bhelgaas@...gle.com>
> >>>
> >>> When disabling PTM, there's no need to clear the Root Select bit.  We
> >>> disable PTM during suspend, and we want to re-enable it during resume.
> >>> Clearing Root Select here makes re-enabling more complicated.
> >>
> >> Currently, it looks like we disable PCI_PTM_CTRL_ROOT in pci_disable_ptm(),
> >> but not enable it in pci_enable_ptm(). Do you know this did not trigger an
> >> issue?
> ...

> > Thanks for asking this, because it reminds me why I didn't add
> > pci_enable_ptm() calls in the resume paths!  That would make them
> > parallel with the suspend paths, which would definitely be nice.  But
> > we would have to rework pci_enable_ptm() to work for Root Ports and
> > Switch Ports as well.  I think we *could* do that.  What do you think?
> 
> IMO, the code will look better if we keep the suspend and resume paths in
> sync. Since we are calling pci_disable_ptm() in suspend path, it makes
> sense to call pci_enable_ptm() in resume path.
> 
> Making the pci_enable_ptm() handle root and upstream ports should not
> be very complicated, right?

I took a stab at it.  pci_enable_ptm() is getting kind of ugly, but
maybe it's better overall.  I'll post it and you can see what you
think.