linux-kernel - Re: [PATCH 2/3] PCI: pciehp: Wait for PDS if in-band presence is disabled

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Date:   Thu, 10 Oct 2019 15:37:28 -0500
From:   Stuart Hayes <stuart.w.hayes@...il.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>,
        Austin Bolen <austin_bolen@...l.com>,
        Keith Busch <keith.busch@...el.com>,
        Alexandru Gagniuc <mr.nuke.me@...il.com>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        "Gustavo A . R . Silva" <gustavo@...eddedor.com>,
        Sinan Kaya <okaya@...nel.org>,
        Oza Pawandeep <poza@...eaurora.org>, linux-pci@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Lukas Wunner <lukas@...ner.de>
Subject: Re: [PATCH 2/3] PCI: pciehp: Wait for PDS if in-band presence is disabled

On Thu, Oct 10, 2019 at 12:40 AM Andy Shevchenko
<andy.shevchenko@...il.com> wrote:
>
> On Thu, Oct 10, 2019 at 8:37 AM Andy Shevchenko
> <andy.shevchenko@...il.com> wrote:
> > On Wed, Oct 9, 2019 at 11:05 PM Stuart Hayes <stuart.w.hayes@...il.com> wrote:
>
> > > +static void pcie_wait_for_presence(struct pci_dev *pdev)
> > > +{
> > > +       int timeout = 1250;
>
> > > +       bool pds;
>
> Also this is redundant. Just use the following outside the loop
>
>  if (!retries)
>    pc_info(...);
>
> .
>
> > > +       u16 slot_status;
> > > +
> > > +       while (true) {
> > > +               pcie_capability_read_word(pdev, PCI_EXP_SLTSTA, &slot_status);
> > > +               pds = !!(slot_status & PCI_EXP_SLTSTA_PDS);
> > > +               if (pds || timeout <= 0)
> > > +                       break;
> > > +               msleep(10);
> > > +               timeout -= 10;
> > > +       }
> >
> > Can we avoid infinite loops? They are hard to parse (in most cases,
> > and especially when it's a timeout loop)
> >
> > unsigned int retries = 125; // 1250 ms
> >
> > do {
> >  ...
> > } while (--retries);
> >
> > > +
> > > +       if (!pds)
> > > +               pci_info(pdev, "Presence Detect state not set in 1250 msec\n");
> > > +}
> >
> > --
> > With Best Regards,
> > Andy Shevchenko
>
>
>
> --
> With Best Regards,
> Andy Shevchenko

Thank you for the feedback!  An infinite loop is used several other places in
this driver--this keeps the style similar.  I can change it as you suggest,
though, if that would be preferable to consistency.