Re: [PATCH v4 2/3] PCI: pciehp: Wait for PDS if in-band presence is disabled

From: Andy Shevchenko <andy.shevchenko@gmail.com>
To: Stuart Hayes <stuart.w.hayes@gmail.com>
Cc: Bjorn Helgaas <bhelgaas@google.com>,
	Austin Bolen <austin_bolen@dell.com>,
	Keith Busch <keith.busch@intel.com>,
	Alexandru Gagniuc <mr.nuke.me@gmail.com>,
	"Rafael J . Wysocki" <rafael.j.wysocki@intel.com>,
	Mika Westerberg <mika.westerberg@linux.intel.com>,
	"Gustavo A . R . Silva" <gustavo@embeddedor.com>,
	Sinan Kaya <okaya@kernel.org>,
	Oza Pawandeep <poza@codeaurora.org>,
	linux-pci@vger.kernel.org,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Lukas Wunner <lukas@wunner.de>
Subject: Re: [PATCH v4 2/3] PCI: pciehp: Wait for PDS if in-band presence is disabled
Date: Fri, 25 Oct 2019 22:16:59 +0300	[thread overview]
Message-ID: <CAHp75Vd54iDEe0ucTW8Gz9Q6cDGnA88XcBMy9-C5P1QuLzDm0Q@mail.gmail.com> (raw)
In-Reply-To: <20191025190047.38130-3-stuart.w.hayes@gmail.com>

On Fri, Oct 25, 2019 at 10:01 PM Stuart Hayes <stuart.w.hayes@gmail.com> wrote:
>
> From: Alexandru Gagniuc <mr.nuke.me@gmail.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.
>

FWIW,
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>


> Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
> Signed-off-by: Stuart Hayes <stuart.w.hayes@gmail.com>
> ---
> v2:
>   replace while(true) loop with do...while
> v3
>   remove unused variable declaration (pds)
>   modify text of warning message
> v4
>   remove "!!" boolean conversion from "if" condition for readability
>
>  drivers/pci/hotplug/pciehp_hpc.c | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
>
> diff --git a/drivers/pci/hotplug/pciehp_hpc.c b/drivers/pci/hotplug/pciehp_hpc.c
> index dc109d521f30..02d95ab27a12 100644
> --- a/drivers/pci/hotplug/pciehp_hpc.c
> +++ b/drivers/pci/hotplug/pciehp_hpc.c
> @@ -242,6 +242,22 @@ static bool pci_bus_check_dev(struct pci_bus *bus, int devfn)
>         return found;
>  }
>
> +static void pcie_wait_for_presence(struct pci_dev *pdev)
> +{
> +       int timeout = 1250;
> +       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, "Timeout waiting for Presence Detect state to be set\n");
> +}
> +
>  int pciehp_check_link_status(struct controller *ctrl)
>  {
>         struct pci_dev *pdev = ctrl_dev(ctrl);
> @@ -251,6 +267,9 @@ int pciehp_check_link_status(struct controller *ctrl)
>         if (!pcie_wait_for_link(pdev, true))
>                 return -1;
>
> +       if (ctrl->inband_presence_disabled)
> +               pcie_wait_for_presence(pdev);
> +
>         found = pci_bus_check_dev(ctrl->pcie->port->subordinate,
>                                         PCI_DEVFN(0, 0));
>
> --
> 2.18.1
>


-- 
With Best Regards,
Andy Shevchenko