linux-kernel - Re: [PATCH] nvme-pci: Allow PCI bus-level PM to be used if ASPM is disabled

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Date:   Thu, 8 Aug 2019 11:06:17 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Christoph Hellwig <hch@....de>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        linux-nvme <linux-nvme@...ts.infradead.org>,
        Keith Busch <kbusch@...nel.org>,
        Mario Limonciello <Mario.Limonciello@...l.com>,
        Kai-Heng Feng <kai.heng.feng@...onical.com>,
        Keith Busch <keith.busch@...el.com>,
        Sagi Grimberg <sagi@...mberg.me>,
        Linux PM <linux-pm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Rajat Jain <rajatja@...gle.com>,
        Linux PCI <linux-pci@...r.kernel.org>,
        Bjorn Helgaas <helgaas@...nel.org>
Subject: Re: [PATCH] nvme-pci: Allow PCI bus-level PM to be used if ASPM is disabled

On Thu, Aug 8, 2019 at 10:48 AM Christoph Hellwig <hch@....de> wrote:
>
> > -     ndev->last_ps = 0;
> >       ret = nvme_get_power_state(ctrl, &ndev->last_ps);
> > -     if (ret < 0)
> > +     if (ret < 0 || ndev->last_ps == U32_MAX)
>
> Is the intent of the magic U32_MAX check to see if the
> nvme_get_power_state failed at the nvme level?  In that case just
> checking for any non-zero return value from nvme_get_power_state might
> be the easier and more clear way to do it.

Now that I think of that, it appears redundant.  I'll drop it.

>
> > Index: linux-pm/drivers/pci/pcie/aspm.c
> > ===================================================================
> > --- linux-pm.orig/drivers/pci/pcie/aspm.c
> > +++ linux-pm/drivers/pci/pcie/aspm.c
>
> Shouldn't we split PCI vs nvme in two patches?

That can be done.

> > @@ -1170,6 +1170,26 @@ static int pcie_aspm_get_policy(char *bu
> >  module_param_call(policy, pcie_aspm_set_policy, pcie_aspm_get_policy,
> >       NULL, 0644);
> >
> > +/*
> > + * pcie_aspm_enabled - Return the mask of enabled ASPM link states.
> > + * @pci_device: Target device.
> > + */
> > +u32 pcie_aspm_enabled(struct pci_dev *pci_device)
>
> pcie_aspm_enabled sounds like it returns a boolean.  Shouldn't there be
> a mask or so in the name better documenting what it returns?

OK

> > +{
> > +     struct pci_dev *bridge = pci_upstream_bridge(pci_device);
> > +     u32 ret;
> > +
> > +     if (!bridge)
> > +             return 0;
> > +
> > +     mutex_lock(&aspm_lock);
> > +     ret = bridge->link_state ? bridge->link_state->aspm_enabled : 0;
> > +     mutex_unlock(&aspm_lock);
> > +
> > +     return ret;
> > +}
>
> I think this will need a EXPORT_SYMBOL_GPL thrown in so that modular
> nvme continues working.

Right, sorry.

> > +
> > +
> >  #ifdef CONFIG_PCIEASPM_DEBUG
>
> Nit: double blank line here.

Overlooked, will fix.

Thanks!