linux-kernel - Re: [PATCH v2 2/3] PCI: pciehp: Wait for PDS if in-band presence is disabled

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Message-ID: <CAHp75VdDWQ=t=JiMei5bJGE59P70yxbfx48j6ufp32aHz2mM3g@mail.gmail.com>
Date:   Sat, 12 Oct 2019 10:34:35 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Stuart Hayes <stuart.w.hayes@...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 v2 2/3] PCI: pciehp: Wait for PDS if in-band presence is disabled

On Fri, Oct 11, 2019 at 11:51 PM Stuart Hayes <stuart.w.hayes@...il.com> wrote:
>
> From: Alexandru Gagniuc <mr.nuke.me@...il.com>
>
> When inband presence is disabled, PDS may come up at any time, or not
> at all. PDS being low may indicate that the card is still mating, and
> we could expect contact bounce to bring down the link as well.
>
> It is reasonable to assume that most cards will mate in a hotplug slot
> in about a second. Thus, when we know PDS only reflects out-of-band
> presence, it's worthwhile to wait the extra second or so to make sure
> the card is properly mated before loading the driver, and to prevent
> the hotplug code from disabling a device if the presence detect change
> goes active after the device is enabled.

Thank you!
My comments below.

> +static void pcie_wait_for_presence(struct pci_dev *pdev)
> +{
> +       int timeout = 1250;

> +       bool pds;

make W=1 will issue a warning. Just remove the line.

> +       u16 slot_status;
> +
> +       do {
> +               pcie_capability_read_word(pdev, PCI_EXP_SLTSTA, &slot_status);
> +               if (!!(slot_status & PCI_EXP_SLTSTA_PDS))
> +                       return;
> +               msleep(10);
> +               timeout -= 10;
> +       } while (timeout > 0);
> +

> +       pci_info(pdev, "Presence Detect state not set in 1250 msec\n");

Perhaps ("%d", timeout) ?

> +}

-- 
With Best Regards,
Andy Shevchenko