linux-kernel - Re: [PATCH v3 2/3] PCI: pciehp: Wait for PDS if in-band presence is disabled

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Date:   Mon, 21 Oct 2019 16:41:11 +0300
From:   Mika Westerberg <mika.westerberg@...ux.intel.com>
To:     Stuart Hayes <stuart.w.hayes@...il.com>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>,
        Austin Bolen <austin_bolen@...l.com>, keith.busch@...el.com,
        Alexandru Gagniuc <mr.nuke.me@...il.com>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Andy Shevchenko <andy.shevchenko@...il.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@...r.kernel.org, lukas@...ner.de
Subject: Re: [PATCH v3 2/3] PCI: pciehp: Wait for PDS if in-band presence is
 disabled

On Thu, Oct 17, 2019 at 03:32:55PM -0400, Stuart Hayes 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.
> 
> Signed-off-by: Alexandru Gagniuc <mr.nuke.me@...il.com>
> Signed-off-by: Stuart Hayes <stuart.w.hayes@...il.com>

Reviewed-by: Mika Westerberg <mika.westerberg@...ux.intel.com>

One nit below.

> ---
> v2:
>   replace while(true) loop with do...while
> v3
>   remove unused variable declaration (pds)
>   modify text of warning message
> 
>  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..02eb811a014f 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))

It is more readable if you write it like:

		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